Extract MCP helper types into codex-mcp-types

Move the stable MCP sandbox state and qualified tool-name helpers into a tiny leaf crate, while keeping codex-core re-exports in place so existing callsites stay unchanged.

Co-authored-by: Codex <noreply@openai.com>

codex-rs/Cargo.lock

@@ -1844,11 +1844,13 @@ dependencies = [
  "codex-config",
  "codex-connectors",
  "codex-environment",
+ "codex-exec-server",
  "codex-execpolicy",
  "codex-file-search",
  "codex-git",
  "codex-hooks",
  "codex-keyring-store",
+ "codex-mcp-types",
  "codex-network-proxy",
  "codex-otel",
  "codex-protocol",
@@ -1859,6 +1861,7 @@ dependencies = [
  "codex-skills",
  "codex-state",
  "codex-test-macros",
+ "codex-tool-spec",
  "codex-utils-absolute-path",
  "codex-utils-cache",
  "codex-utils-cargo-bin",
@@ -2003,6 +2006,27 @@ dependencies = [
  "wiremock",
 ]
 
+[[package]]
+name = "codex-exec-server"
+version = "0.0.0"
+dependencies = [
+ "anyhow",
+ "base64 0.22.1",
+ "clap",
+ "codex-app-server-protocol",
+ "codex-environment",
+ "codex-utils-cargo-bin",
+ "codex-utils-pty",
+ "futures",
+ "pretty_assertions",
+ "serde",
+ "serde_json",
+ "thiserror 2.0.18",
+ "tokio",
+ "tokio-tungstenite",
+ "tracing",
+]
+
 [[package]]
 name = "codex-execpolicy"
 version = "0.0.0"
@@ -2207,6 +2231,14 @@ dependencies = [
  "wiremock",
 ]
 
+[[package]]
+name = "codex-mcp-types"
+version = "0.0.0"
+dependencies = [
+ "codex-protocol",
+ "serde",
+]
+
 [[package]]
 name = "codex-network-proxy"
 version = "0.0.0"
@@ -2503,6 +2535,14 @@ dependencies = [
  "syn 2.0.114",
 ]
 
+[[package]]
+name = "codex-tool-spec"
+version = "0.0.0"
+dependencies = [
+ "serde",
+ "serde_json",
+]
+
 [[package]]
 name = "codex-tui"
 version = "0.0.0"

codex-rs/Cargo.toml

@@ -26,6 +26,7 @@ members = [
     "hooks",
     "secrets",
     "exec",
+    "exec-server",
     "execpolicy",
     "execpolicy-legacy",
     "keyring-store",
@@ -33,6 +34,7 @@ members = [
     "linux-sandbox",
     "lmstudio",
     "login",
+    "mcp-types",
     "mcp-server",
     "network-proxy",
     "ollama",
@@ -68,6 +70,7 @@ members = [
     "state",
     "codex-experimental-api-macros",
     "test-macros",
+    "tool-spec",
     "package-manager",
     "artifacts",
 ]
@@ -106,6 +109,7 @@ codex-config = { path = "config" }
 codex-core = { path = "core" }
 codex-environment = { path = "environment" }
 codex-exec = { path = "exec" }
+codex-exec-server = { path = "exec-server" }
 codex-execpolicy = { path = "execpolicy" }
 codex-experimental-api-macros = { path = "codex-experimental-api-macros" }
 codex-feedback = { path = "feedback" }
@@ -116,6 +120,7 @@ codex-keyring-store = { path = "keyring-store" }
 codex-linux-sandbox = { path = "linux-sandbox" }
 codex-lmstudio = { path = "lmstudio" }
 codex-login = { path = "login" }
+codex-mcp-types = { path = "mcp-types" }
 codex-mcp-server = { path = "mcp-server" }
 codex-network-proxy = { path = "network-proxy" }
 codex-ollama = { path = "ollama" }
@@ -131,6 +136,7 @@ codex-skills = { path = "skills" }
 codex-state = { path = "state" }
 codex-stdio-to-uds = { path = "stdio-to-uds" }
 codex-test-macros = { path = "test-macros" }
+codex-tool-spec = { path = "tool-spec" }
 codex-tui = { path = "tui" }
 codex-tui-app-server = { path = "tui_app_server" }
 codex-utils-absolute-path = { path = "utils/absolute-path" }

codex-rs/app-server/src/fs_api.rs

@@ -34,7 +34,7 @@ pub(crate) struct FsApi {
 impl Default for FsApi {
     fn default() -> Self {
         Self {
-            file_system: Arc::new(Environment.get_filesystem()),
+            file_system: Environment::default().get_filesystem(),
         }
     }
 }

codex-rs/core/Cargo.toml

@@ -35,13 +35,16 @@ codex-client = { workspace = true }
 codex-connectors = { workspace = true }
 codex-config = { workspace = true }
 codex-environment = { workspace = true }
+codex-exec-server = { workspace = true }
 codex-shell-command = { workspace = true }
 codex-skills = { workspace = true }
+codex-tool-spec = { workspace = true }
 codex-execpolicy = { workspace = true }
 codex-file-search = { workspace = true }
 codex-git = { workspace = true }
 codex-hooks = { workspace = true }
 codex-keyring-store = { workspace = true }
+codex-mcp-types = { workspace = true }
 codex-network-proxy = { workspace = true }
 codex-otel = { workspace = true }
 codex-artifacts = { workspace = true }
@@ -92,7 +95,6 @@ sha2 = { workspace = true }
 shlex = { workspace = true }
 similar = { workspace = true }
 tempfile = { workspace = true }
-test-log = { workspace = true }
 thiserror = { workspace = true }
 time = { workspace = true, features = [
     "formatting",
@@ -166,6 +168,7 @@ opentelemetry = { workspace = true }
 predicates = { workspace = true }
 pretty_assertions = { workspace = true }
 test-case = "3.3.1"
+test-log = { workspace = true }
 opentelemetry_sdk = { workspace = true, features = [
     "experimental_metrics_custom_reader",
     "metrics",

codex-rs/core/config.schema.json

@@ -1915,6 +1915,18 @@
       "description": "Experimental / do not use. Replaces the synthesized realtime startup context appended to websocket session instructions. An empty string disables startup context injection entirely.",
       "type": "string"
     },
+    "experimental_unified_exec_exec_server_websocket_url": {
+      "description": "Optional websocket URL for connecting to an existing `codex-exec-server`.",
+      "type": "string"
+    },
+    "experimental_unified_exec_exec_server_workspace_root": {
+      "allOf": [
+        {
+          "$ref": "#/definitions/AbsolutePathBuf"
+        }
+      ],
+      "description": "Optional absolute path to the executor-visible workspace root that corresponds to the local session cwd."
+    },
     "experimental_use_freeform_apply_patch": {
       "type": "boolean"
     },

codex-rs/core/src/client.rs

@@ -94,6 +94,7 @@ use crate::auth::RefreshTokenError;
 use crate::client_common::Prompt;
 use crate::client_common::ResponseEvent;
 use crate::client_common::ResponseStream;
+use crate::client_common::create_tools_json_for_responses_api;
 use crate::default_client::build_reqwest_client;
 use crate::error::CodexErr;
 use crate::error::Result;
@@ -104,7 +105,6 @@ use crate::response_debug_context::extract_response_debug_context;
 use crate::response_debug_context::extract_response_debug_context_from_api_error;
 use crate::response_debug_context::telemetry_api_error_message;
 use crate::response_debug_context::telemetry_transport_error_message;
-use crate::tools::spec::create_tools_json_for_responses_api;
 use crate::util::FeedbackRequestTags;
 use crate::util::emit_feedback_auth_recovery_tags;
 use crate::util::emit_feedback_request_tags_with_auth_env;

codex-rs/core/src/client_common.rs

@@ -14,6 +14,8 @@ use std::task::Context;
 use std::task::Poll;
 use tokio::sync::mpsc;
 
+mod tools_json;
+
 /// Review thread system prompt. Edit `core/src/review_prompt.md` to customize.
 pub const REVIEW_PROMPT: &str = include_str!("../review_prompt.md");
 
@@ -44,6 +46,8 @@ pub struct Prompt {
     pub output_schema: Option<Value>,
 }
 
+pub(crate) use tools_json::create_tools_json_for_responses_api;
+
 impl Prompt {
     pub(crate) fn get_formatted_input(&self) -> Vec<ResponseItem> {
         let mut input = self.input.clone();

codex-rs/core/src/client_common/tools_json.rs

@@ -0,0 +1,23 @@
+use crate::error::Result;
+
+use super::tools::ToolSpec;
+
+/// Returns JSON values that are compatible with Function Calling in the
+/// Responses API:
+/// https://platform.openai.com/docs/guides/function-calling?api-mode=responses
+///
+/// This helper intentionally lives under `client_common` so the model client
+/// can serialize tools without depending on the full tool registry builder in
+/// `tools/spec.rs`.
+pub(crate) fn create_tools_json_for_responses_api(
+    tools: &[ToolSpec],
+) -> Result<Vec<serde_json::Value>> {
+    let mut tools_json = Vec::new();
+
+    for tool in tools {
+        let json = serde_json::to_value(tool)?;
+        tools_json.push(json);
+    }
+
+    Ok(tools_json)
+}

codex-rs/core/src/client_tools.rs

@@ -0,0 +1,12 @@
+use serde::Serialize;
+use serde_json::Value;
+
+use crate::error::Result;
+
+pub(crate) fn create_tools_json_for_responses_api<T: Serialize>(tools: &[T]) -> Result<Vec<Value>> {
+    tools
+        .iter()
+        .map(serde_json::to_value)
+        .collect::<serde_json::Result<Vec<_>>>()
+        .map_err(Into::into)
+}

codex-rs/core/src/codex.rs

@@ -312,6 +312,7 @@ use crate::turn_diff_tracker::TurnDiffTracker;
 use crate::turn_timing::TurnTimingState;
 use crate::turn_timing::record_turn_ttfm_metric;
 use crate::turn_timing::record_turn_ttft_metric;
+use crate::unified_exec::RemoteExecServerBackend;
 use crate::unified_exec::UnifiedExecProcessManager;
 use crate::util::backoff;
 use crate::windows_sandbox::WindowsSandboxLevelExt;
@@ -1772,6 +1773,13 @@ impl Session {
             });
         }
 
+        let remote_exec_server =
+            RemoteExecServerBackend::connect_for_config(config.as_ref()).await?;
+        let environment = remote_exec_server
+            .as_ref()
+            .map(|backend| Environment::with_file_system(Arc::new(backend.file_system())))
+            .unwrap_or_default();
+
         let services = SessionServices {
             // Initialize the MCP connection manager with an uninitialized
             // instance. It will be replaced with one created via
@@ -1784,8 +1792,9 @@ impl Session {
                 &config.permissions.approval_policy,
             ))),
             mcp_startup_cancellation_token: Mutex::new(CancellationToken::new()),
-            unified_exec_manager: UnifiedExecProcessManager::new(
+            unified_exec_manager: UnifiedExecProcessManager::with_remote_exec_server(
                 config.background_terminal_max_timeout,
+                remote_exec_server,
             ),
             shell_zsh_path: config.zsh_path.clone(),
             main_execve_wrapper_exe: config.main_execve_wrapper_exe.clone(),
@@ -1825,7 +1834,7 @@ impl Session {
             code_mode_service: crate::tools::code_mode::CodeModeService::new(
                 config.js_repl_node_path.clone(),
             ),
-            environment: Arc::new(Environment),
+            environment: Arc::new(environment),
         };
         let js_repl = Arc::new(JsReplHandle::with_node_path(
             config.js_repl_node_path.clone(),
@@ -1907,6 +1916,7 @@ impl Session {
             *cancel_guard = CancellationToken::new();
         }
         let (mcp_connection_manager, cancel_token) = McpConnectionManager::new(
+            INITIAL_SUBMIT_ID.to_owned(),
             &mcp_servers,
             config.mcp_oauth_credentials_store_mode,
             auth_statuses.clone(),
@@ -4042,6 +4052,7 @@ impl Session {
             *guard = CancellationToken::new();
         }
         let (refreshed_manager, cancel_token) = McpConnectionManager::new(
+            INITIAL_SUBMIT_ID.to_owned(),
             &mcp_servers,
             store_mode,
             auth_statuses,
@@ -4374,774 +4385,7 @@ fn submission_dispatch_span(sub: &Submission) -> tracing::Span {
 }
 
 /// Operation handlers
-mod handlers {
-    use crate::codex::Session;
-    use crate::codex::SessionSettingsUpdate;
-    use crate::codex::SteerInputError;
-
-    use crate::codex::spawn_review_thread;
-    use crate::config::Config;
-
-    use crate::mcp::auth::compute_auth_statuses;
-    use crate::mcp::collect_mcp_snapshot_from_manager;
-    use crate::review_prompts::resolve_review_request;
-    use crate::rollout::RolloutRecorder;
-    use crate::rollout::session_index;
-    use crate::tasks::CompactTask;
-    use crate::tasks::UndoTask;
-    use crate::tasks::UserShellCommandMode;
-    use crate::tasks::UserShellCommandTask;
-    use crate::tasks::execute_user_shell_command;
-    use codex_protocol::custom_prompts::CustomPrompt;
-    use codex_protocol::protocol::CodexErrorInfo;
-    use codex_protocol::protocol::ErrorEvent;
-    use codex_protocol::protocol::Event;
-    use codex_protocol::protocol::EventMsg;
-    use codex_protocol::protocol::ListCustomPromptsResponseEvent;
-    use codex_protocol::protocol::ListSkillsResponseEvent;
-    use codex_protocol::protocol::McpServerRefreshConfig;
-    use codex_protocol::protocol::Op;
-    use codex_protocol::protocol::ReviewDecision;
-    use codex_protocol::protocol::ReviewRequest;
-    use codex_protocol::protocol::RolloutItem;
-    use codex_protocol::protocol::SkillsListEntry;
-    use codex_protocol::protocol::ThreadNameUpdatedEvent;
-    use codex_protocol::protocol::ThreadRolledBackEvent;
-    use codex_protocol::protocol::TurnAbortReason;
-    use codex_protocol::protocol::WarningEvent;
-    use codex_protocol::request_permissions::RequestPermissionsResponse;
-    use codex_protocol::request_user_input::RequestUserInputResponse;
-
-    use crate::context_manager::is_user_turn_boundary;
-    use codex_protocol::config_types::CollaborationMode;
-    use codex_protocol::config_types::ModeKind;
-    use codex_protocol::config_types::Settings;
-    use codex_protocol::dynamic_tools::DynamicToolResponse;
-    use codex_protocol::mcp::RequestId as ProtocolRequestId;
-    use codex_protocol::user_input::UserInput;
-    use codex_rmcp_client::ElicitationAction;
-    use codex_rmcp_client::ElicitationResponse;
-    use serde_json::Value;
-    use std::path::PathBuf;
-    use std::sync::Arc;
-    use tracing::info;
-    use tracing::warn;
-
-    pub async fn interrupt(sess: &Arc<Session>) {
-        sess.interrupt_task().await;
-    }
-
-    pub async fn clean_background_terminals(sess: &Arc<Session>) {
-        sess.close_unified_exec_processes().await;
-    }
-
-    pub async fn override_turn_context(
-        sess: &Session,
-        sub_id: String,
-        updates: SessionSettingsUpdate,
-    ) {
-        if let Err(err) = sess.update_settings(updates).await {
-            sess.send_event_raw(Event {
-                id: sub_id,
-                msg: EventMsg::Error(ErrorEvent {
-                    message: err.to_string(),
-                    codex_error_info: Some(CodexErrorInfo::BadRequest),
-                }),
-            })
-            .await;
-        }
-    }
-
-    pub async fn user_input_or_turn(sess: &Arc<Session>, sub_id: String, op: Op) {
-        let (items, updates) = match op {
-            Op::UserTurn {
-                cwd,
-                approval_policy,
-                sandbox_policy,
-                model,
-                effort,
-                summary,
-                service_tier,
-                final_output_json_schema,
-                items,
-                collaboration_mode,
-                personality,
-            } => {
-                let collaboration_mode = collaboration_mode.or_else(|| {
-                    Some(CollaborationMode {
-                        mode: ModeKind::Default,
-                        settings: Settings {
-                            model: model.clone(),
-                            reasoning_effort: effort,
-                            developer_instructions: None,
-                        },
-                    })
-                });
-                (
-                    items,
-                    SessionSettingsUpdate {
-                        cwd: Some(cwd),
-                        approval_policy: Some(approval_policy),
-                        approvals_reviewer: None,
-                        sandbox_policy: Some(sandbox_policy),
-                        windows_sandbox_level: None,
-                        collaboration_mode,
-                        reasoning_summary: summary,
-                        service_tier,
-                        final_output_json_schema: Some(final_output_json_schema),
-                        personality,
-                        app_server_client_name: None,
-                    },
-                )
-            }
-            Op::UserInput {
-                items,
-                final_output_json_schema,
-            } => (
-                items,
-                SessionSettingsUpdate {
-                    final_output_json_schema: Some(final_output_json_schema),
-                    ..Default::default()
-                },
-            ),
-            _ => unreachable!(),
-        };
-
-        let Ok(current_context) = sess.new_turn_with_sub_id(sub_id, updates).await else {
-            // new_turn_with_sub_id already emits the error event.
-            return;
-        };
-        sess.maybe_emit_unknown_model_warning_for_turn(current_context.as_ref())
-            .await;
-        current_context.session_telemetry.user_prompt(&items);
-
-        // Attempt to inject input into current task.
-        if let Err(SteerInputError::NoActiveTurn(items)) =
-            sess.steer_input(items, /*expected_turn_id*/ None).await
-        {
-            sess.refresh_mcp_servers_if_requested(&current_context)
-                .await;
-            sess.spawn_task(
-                Arc::clone(&current_context),
-                items,
-                crate::tasks::RegularTask::new(),
-            )
-            .await;
-        }
-    }
-
-    pub async fn run_user_shell_command(sess: &Arc<Session>, sub_id: String, command: String) {
-        if let Some((turn_context, cancellation_token)) =
-            sess.active_turn_context_and_cancellation_token().await
-        {
-            let session = Arc::clone(sess);
-            tokio::spawn(async move {
-                execute_user_shell_command(
-                    session,
-                    turn_context,
-                    command,
-                    cancellation_token,
-                    UserShellCommandMode::ActiveTurnAuxiliary,
-                )
-                .await;
-            });
-            return;
-        }
-
-        let turn_context = sess.new_default_turn_with_sub_id(sub_id).await;
-        sess.spawn_task(
-            Arc::clone(&turn_context),
-            Vec::new(),
-            UserShellCommandTask::new(command),
-        )
-        .await;
-    }
-
-    pub async fn resolve_elicitation(
-        sess: &Arc<Session>,
-        server_name: String,
-        request_id: ProtocolRequestId,
-        decision: codex_protocol::approvals::ElicitationAction,
-        content: Option<Value>,
-        meta: Option<Value>,
-    ) {
-        let action = match decision {
-            codex_protocol::approvals::ElicitationAction::Accept => ElicitationAction::Accept,
-            codex_protocol::approvals::ElicitationAction::Decline => ElicitationAction::Decline,
-            codex_protocol::approvals::ElicitationAction::Cancel => ElicitationAction::Cancel,
-        };
-        let content = match action {
-            // Preserve the legacy fallback for clients that only send an action.
-            ElicitationAction::Accept => Some(content.unwrap_or_else(|| serde_json::json!({}))),
-            ElicitationAction::Decline | ElicitationAction::Cancel => None,
-        };
-        let response = ElicitationResponse {
-            action,
-            content,
-            meta,
-        };
-        let request_id = match request_id {
-            ProtocolRequestId::String(value) => {
-                rmcp::model::NumberOrString::String(std::sync::Arc::from(value))
-            }
-            ProtocolRequestId::Integer(value) => rmcp::model::NumberOrString::Number(value),
-        };
-        if let Err(err) = sess
-            .resolve_elicitation(server_name, request_id, response)
-            .await
-        {
-            warn!(
-                error = %err,
-                "failed to resolve elicitation request in session"
-            );
-        }
-    }
-
-    /// Propagate a user's exec approval decision to the session.
-    /// Also optionally applies an execpolicy amendment.
-    pub async fn exec_approval(
-        sess: &Arc<Session>,
-        approval_id: String,
-        turn_id: Option<String>,
-        decision: ReviewDecision,
-    ) {
-        let event_turn_id = turn_id.unwrap_or_else(|| approval_id.clone());
-        if let ReviewDecision::ApprovedExecpolicyAmendment {
-            proposed_execpolicy_amendment,
-        } = &decision
-        {
-            match sess
-                .persist_execpolicy_amendment(proposed_execpolicy_amendment)
-                .await
-            {
-                Ok(()) => {
-                    sess.record_execpolicy_amendment_message(
-                        &event_turn_id,
-                        proposed_execpolicy_amendment,
-                    )
-                    .await;
-                }
-                Err(err) => {
-                    let message = format!("Failed to apply execpolicy amendment: {err}");
-                    tracing::warn!("{message}");
-                    let warning = EventMsg::Warning(WarningEvent { message });
-                    sess.send_event_raw(Event {
-                        id: event_turn_id.clone(),
-                        msg: warning,
-                    })
-                    .await;
-                }
-            }
-        }
-        match decision {
-            ReviewDecision::Abort => {
-                sess.interrupt_task().await;
-            }
-            other => sess.notify_approval(&approval_id, other).await,
-        }
-    }
-
-    pub async fn patch_approval(sess: &Arc<Session>, id: String, decision: ReviewDecision) {
-        match decision {
-            ReviewDecision::Abort => {
-                sess.interrupt_task().await;
-            }
-            other => sess.notify_approval(&id, other).await,
-        }
-    }
-
-    pub async fn request_user_input_response(
-        sess: &Arc<Session>,
-        id: String,
-        response: RequestUserInputResponse,
-    ) {
-        sess.notify_user_input_response(&id, response).await;
-    }
-
-    pub async fn request_permissions_response(
-        sess: &Arc<Session>,
-        id: String,
-        response: RequestPermissionsResponse,
-    ) {
-        sess.notify_request_permissions_response(&id, response)
-            .await;
-    }
-
-    pub async fn dynamic_tool_response(
-        sess: &Arc<Session>,
-        id: String,
-        response: DynamicToolResponse,
-    ) {
-        sess.notify_dynamic_tool_response(&id, response).await;
-    }
-
-    pub async fn add_to_history(sess: &Arc<Session>, config: &Arc<Config>, text: String) {
-        let id = sess.conversation_id;
-        let config = Arc::clone(config);
-        tokio::spawn(async move {
-            if let Err(e) = crate::message_history::append_entry(&text, &id, &config).await {
-                warn!("failed to append to message history: {e}");
-            }
-        });
-    }
-
-    pub async fn get_history_entry_request(
-        sess: &Arc<Session>,
-        config: &Arc<Config>,
-        sub_id: String,
-        offset: usize,
-        log_id: u64,
-    ) {
-        let config = Arc::clone(config);
-        let sess_clone = Arc::clone(sess);
-
-        tokio::spawn(async move {
-            // Run lookup in blocking thread because it does file IO + locking.
-            let entry_opt = tokio::task::spawn_blocking(move || {
-                crate::message_history::lookup(log_id, offset, &config)
-            })
-            .await
-            .unwrap_or(None);
-
-            let event = Event {
-                id: sub_id,
-                msg: EventMsg::GetHistoryEntryResponse(
-                    crate::protocol::GetHistoryEntryResponseEvent {
-                        offset,
-                        log_id,
-                        entry: entry_opt.map(|e| codex_protocol::message_history::HistoryEntry {
-                            conversation_id: e.session_id,
-                            ts: e.ts,
-                            text: e.text,
-                        }),
-                    },
-                ),
-            };
-
-            sess_clone.send_event_raw(event).await;
-        });
-    }
-
-    pub async fn refresh_mcp_servers(sess: &Arc<Session>, refresh_config: McpServerRefreshConfig) {
-        let mut guard = sess.pending_mcp_server_refresh_config.lock().await;
-        *guard = Some(refresh_config);
-    }
-
-    pub async fn reload_user_config(sess: &Arc<Session>) {
-        sess.reload_user_config_layer().await;
-    }
-
-    pub async fn list_mcp_tools(sess: &Session, config: &Arc<Config>, sub_id: String) {
-        let mcp_connection_manager = sess.services.mcp_connection_manager.read().await;
-        let auth = sess.services.auth_manager.auth().await;
-        let mcp_servers = sess
-            .services
-            .mcp_manager
-            .effective_servers(config, auth.as_ref());
-        let snapshot = collect_mcp_snapshot_from_manager(
-            &mcp_connection_manager,
-            compute_auth_statuses(mcp_servers.iter(), config.mcp_oauth_credentials_store_mode)
-                .await,
-        )
-        .await;
-        let event = Event {
-            id: sub_id,
-            msg: EventMsg::McpListToolsResponse(snapshot),
-        };
-        sess.send_event_raw(event).await;
-    }
-
-    pub async fn list_custom_prompts(sess: &Session, sub_id: String) {
-        let custom_prompts: Vec<CustomPrompt> =
-            if let Some(dir) = crate::custom_prompts::default_prompts_dir() {
-                crate::custom_prompts::discover_prompts_in(&dir).await
-            } else {
-                Vec::new()
-            };
-
-        let event = Event {
-            id: sub_id,
-            msg: EventMsg::ListCustomPromptsResponse(ListCustomPromptsResponseEvent {
-                custom_prompts,
-            }),
-        };
-        sess.send_event_raw(event).await;
-    }
-
-    pub async fn list_skills(
-        sess: &Session,
-        sub_id: String,
-        cwds: Vec<PathBuf>,
-        force_reload: bool,
-    ) {
-        let (cwds, session_source) = if cwds.is_empty() {
-            let state = sess.state.lock().await;
-            (
-                vec![state.session_configuration.cwd.clone()],
-                state.session_configuration.session_source.clone(),
-            )
-        } else {
-            let state = sess.state.lock().await;
-            (cwds, state.session_configuration.session_source.clone())
-        };
-
-        let skills_manager = &sess.services.skills_manager;
-        let mut skills = Vec::new();
-        for cwd in cwds {
-            let outcome = crate::skills::filter_skill_load_outcome_for_session_source(
-                skills_manager.skills_for_cwd(&cwd, force_reload).await,
-                &session_source,
-            );
-            let errors = super::errors_to_info(&outcome.errors);
-            let skills_metadata = super::skills_to_info(&outcome.skills, &outcome.disabled_paths);
-            skills.push(SkillsListEntry {
-                cwd,
-                skills: skills_metadata,
-                errors,
-            });
-        }
-
-        let event = Event {
-            id: sub_id,
-            msg: EventMsg::ListSkillsResponse(ListSkillsResponseEvent { skills }),
-        };
-        sess.send_event_raw(event).await;
-    }
-
-    pub async fn undo(sess: &Arc<Session>, sub_id: String) {
-        let turn_context = sess.new_default_turn_with_sub_id(sub_id).await;
-        sess.spawn_task(turn_context, Vec::new(), UndoTask::new())
-            .await;
-    }
-
-    pub async fn compact(sess: &Arc<Session>, sub_id: String) {
-        let turn_context = sess.new_default_turn_with_sub_id(sub_id).await;
-
-        sess.spawn_task(
-            Arc::clone(&turn_context),
-            vec![UserInput::Text {
-                text: turn_context.compact_prompt().to_string(),
-                // Compaction prompt is synthesized; no UI element ranges to preserve.
-                text_elements: Vec::new(),
-            }],
-            CompactTask,
-        )
-        .await;
-    }
-
-    pub async fn drop_memories(sess: &Arc<Session>, config: &Arc<Config>, sub_id: String) {
-        let mut errors = Vec::new();
-
-        if let Some(state_db) = sess.services.state_db.as_deref() {
-            if let Err(err) = state_db.clear_memory_data().await {
-                errors.push(format!("failed clearing memory rows from state db: {err}"));
-            }
-        } else {
-            errors.push("state db unavailable; memory rows were not cleared".to_string());
-        }
-
-        let memory_root = crate::memories::memory_root(&config.codex_home);
-        if let Err(err) = crate::memories::clear_memory_root_contents(&memory_root).await {
-            errors.push(format!(
-                "failed clearing memory directory {}: {err}",
-                memory_root.display()
-            ));
-        }
-
-        if errors.is_empty() {
-            sess.send_event_raw(Event {
-                id: sub_id,
-                msg: EventMsg::Warning(WarningEvent {
-                    message: format!(
-                        "Dropped memories at {} and cleared memory rows from state db.",
-                        memory_root.display()
-                    ),
-                }),
-            })
-            .await;
-            return;
-        }
-
-        sess.send_event_raw(Event {
-            id: sub_id,
-            msg: EventMsg::Error(ErrorEvent {
-                message: format!("Memory drop completed with errors: {}", errors.join("; ")),
-                codex_error_info: Some(CodexErrorInfo::Other),
-            }),
-        })
-        .await;
-    }
-
-    pub async fn update_memories(sess: &Arc<Session>, config: &Arc<Config>, sub_id: String) {
-        let session_source = {
-            let state = sess.state.lock().await;
-            state.session_configuration.session_source.clone()
-        };
-
-        crate::memories::start_memories_startup_task(sess, Arc::clone(config), &session_source);
-
-        sess.send_event_raw(Event {
-            id: sub_id.clone(),
-            msg: EventMsg::Warning(WarningEvent {
-                message: "Memory update triggered.".to_string(),
-            }),
-        })
-        .await;
-    }
-
-    pub async fn thread_rollback(sess: &Arc<Session>, sub_id: String, num_turns: u32) {
-        if num_turns == 0 {
-            sess.send_event_raw(Event {
-                id: sub_id,
-                msg: EventMsg::Error(ErrorEvent {
-                    message: "num_turns must be >= 1".to_string(),
-                    codex_error_info: Some(CodexErrorInfo::ThreadRollbackFailed),
-                }),
-            })
-            .await;
-            return;
-        }
-
-        let has_active_turn = { sess.active_turn.lock().await.is_some() };
-        if has_active_turn {
-            sess.send_event_raw(Event {
-                id: sub_id,
-                msg: EventMsg::Error(ErrorEvent {
-                    message: "Cannot rollback while a turn is in progress.".to_string(),
-                    codex_error_info: Some(CodexErrorInfo::ThreadRollbackFailed),
-                }),
-            })
-            .await;
-            return;
-        }
-
-        let turn_context = sess.new_default_turn_with_sub_id(sub_id).await;
-        let rollout_path = {
-            let recorder = {
-                let guard = sess.services.rollout.lock().await;
-                guard.clone()
-            };
-            let Some(recorder) = recorder else {
-                sess.send_event_raw(Event {
-                    id: turn_context.sub_id.clone(),
-                    msg: EventMsg::Error(ErrorEvent {
-                        message: "thread rollback requires a persisted rollout path".to_string(),
-                        codex_error_info: Some(CodexErrorInfo::ThreadRollbackFailed),
-                    }),
-                })
-                .await;
-                return;
-            };
-            recorder.rollout_path().to_path_buf()
-        };
-        if let Some(recorder) = {
-            let guard = sess.services.rollout.lock().await;
-            guard.clone()
-        } && let Err(err) = recorder.flush().await
-        {
-            sess.send_event_raw(Event {
-                id: turn_context.sub_id.clone(),
-                msg: EventMsg::Error(ErrorEvent {
-                    message: format!(
-                        "failed to flush rollout `{}` for rollback replay: {err}",
-                        rollout_path.display()
-                    ),
-                    codex_error_info: Some(CodexErrorInfo::ThreadRollbackFailed),
-                }),
-            })
-            .await;
-            return;
-        }
-
-        let initial_history =
-            match RolloutRecorder::get_rollout_history(rollout_path.as_path()).await {
-                Ok(history) => history,
-                Err(err) => {
-                    sess.send_event_raw(Event {
-                        id: turn_context.sub_id.clone(),
-                        msg: EventMsg::Error(ErrorEvent {
-                            message: format!(
-                                "failed to load rollout `{}` for rollback replay: {err}",
-                                rollout_path.display()
-                            ),
-                            codex_error_info: Some(CodexErrorInfo::ThreadRollbackFailed),
-                        }),
-                    })
-                    .await;
-                    return;
-                }
-            };
-
-        let rollback_event = ThreadRolledBackEvent { num_turns };
-        let rollback_msg = EventMsg::ThreadRolledBack(rollback_event.clone());
-        let replay_items = initial_history
-            .get_rollout_items()
-            .into_iter()
-            .chain(std::iter::once(RolloutItem::EventMsg(rollback_msg.clone())))
-            .collect::<Vec<_>>();
-        sess.persist_rollout_items(&[RolloutItem::EventMsg(rollback_msg.clone())])
-            .await;
-        sess.flush_rollout().await;
-        sess.apply_rollout_reconstruction(turn_context.as_ref(), replay_items.as_slice())
-            .await;
-        sess.recompute_token_usage(turn_context.as_ref()).await;
-
-        sess.deliver_event_raw(Event {
-            id: turn_context.sub_id.clone(),
-            msg: rollback_msg,
-        })
-        .await;
-    }
-
-    /// Persists the thread name in the session index, updates in-memory state, and emits
-    /// a `ThreadNameUpdated` event on success.
-    ///
-    /// This appends the name to `CODEX_HOME/sessions_index.jsonl` via `session_index::append_thread_name` for the
-    /// current `thread_id`, then updates `SessionConfiguration::thread_name`.
-    ///
-    /// Returns an error event if the name is empty or session persistence is disabled.
-    pub async fn set_thread_name(sess: &Arc<Session>, sub_id: String, name: String) {
-        let Some(name) = crate::util::normalize_thread_name(&name) else {
-            let event = Event {
-                id: sub_id,
-                msg: EventMsg::Error(ErrorEvent {
-                    message: "Thread name cannot be empty.".to_string(),
-                    codex_error_info: Some(CodexErrorInfo::BadRequest),
-                }),
-            };
-            sess.send_event_raw(event).await;
-            return;
-        };
-
-        let persistence_enabled = {
-            let rollout = sess.services.rollout.lock().await;
-            rollout.is_some()
-        };
-        if !persistence_enabled {
-            let event = Event {
-                id: sub_id,
-                msg: EventMsg::Error(ErrorEvent {
-                    message: "Session persistence is disabled; cannot rename thread.".to_string(),
-                    codex_error_info: Some(CodexErrorInfo::Other),
-                }),
-            };
-            sess.send_event_raw(event).await;
-            return;
-        };
-
-        let codex_home = sess.codex_home().await;
-        if let Err(e) =
-            session_index::append_thread_name(&codex_home, sess.conversation_id, &name).await
-        {
-            let event = Event {
-                id: sub_id,
-                msg: EventMsg::Error(ErrorEvent {
-                    message: format!("Failed to set thread name: {e}"),
-                    codex_error_info: Some(CodexErrorInfo::Other),
-                }),
-            };
-            sess.send_event_raw(event).await;
-            return;
-        }
-
-        {
-            let mut state = sess.state.lock().await;
-            state.session_configuration.thread_name = Some(name.clone());
-        }
-
-        sess.send_event_raw(Event {
-            id: sub_id,
-            msg: EventMsg::ThreadNameUpdated(ThreadNameUpdatedEvent {
-                thread_id: sess.conversation_id,
-                thread_name: Some(name),
-            }),
-        })
-        .await;
-    }
-
-    pub async fn shutdown(sess: &Arc<Session>, sub_id: String) -> bool {
-        sess.abort_all_tasks(TurnAbortReason::Interrupted).await;
-        let _ = sess.conversation.shutdown().await;
-        sess.services
-            .unified_exec_manager
-            .terminate_all_processes()
-            .await;
-        sess.guardian_review_session.shutdown().await;
-        info!("Shutting down Codex instance");
-        let history = sess.clone_history().await;
-        let turn_count = history
-            .raw_items()
-            .iter()
-            .filter(|item| is_user_turn_boundary(item))
-            .count();
-        sess.services.session_telemetry.counter(
-            "codex.conversation.turn.count",
-            i64::try_from(turn_count).unwrap_or(0),
-            &[],
-        );
-
-        // Gracefully flush and shutdown rollout recorder on session end so tests
-        // that inspect the rollout file do not race with the background writer.
-        let recorder_opt = {
-            let mut guard = sess.services.rollout.lock().await;
-            guard.take()
-        };
-        if let Some(rec) = recorder_opt
-            && let Err(e) = rec.shutdown().await
-        {
-            warn!("failed to shutdown rollout recorder: {e}");
-            let event = Event {
-                id: sub_id.clone(),
-                msg: EventMsg::Error(ErrorEvent {
-                    message: "Failed to shutdown rollout recorder".to_string(),
-                    codex_error_info: Some(CodexErrorInfo::Other),
-                }),
-            };
-            sess.send_event_raw(event).await;
-        }
-
-        let event = Event {
-            id: sub_id,
-            msg: EventMsg::ShutdownComplete,
-        };
-        sess.send_event_raw(event).await;
-        true
-    }
-
-    pub async fn review(
-        sess: &Arc<Session>,
-        config: &Arc<Config>,
-        sub_id: String,
-        review_request: ReviewRequest,
-    ) {
-        let turn_context = sess.new_default_turn_with_sub_id(sub_id.clone()).await;
-        sess.maybe_emit_unknown_model_warning_for_turn(turn_context.as_ref())
-            .await;
-        sess.refresh_mcp_servers_if_requested(&turn_context).await;
-        match resolve_review_request(review_request, turn_context.cwd.as_path()) {
-            Ok(resolved) => {
-                spawn_review_thread(
-                    Arc::clone(sess),
-                    Arc::clone(config),
-                    turn_context.clone(),
-                    sub_id,
-                    resolved,
-                )
-                .await;
-            }
-            Err(err) => {
-                let event = Event {
-                    id: sub_id,
-                    msg: EventMsg::Error(ErrorEvent {
-                        message: err.to_string(),
-                        codex_error_info: Some(CodexErrorInfo::Other),
-                    }),
-                };
-                sess.send_event(&turn_context, event.msg).await;
-            }
-        }
-    }
-}
+mod handlers;
 
 /// Spawn a review thread using the given prompt.
 async fn spawn_review_thread(

codex-rs/core/src/codex/handlers.rs

@@ -0,0 +1,747 @@
+use crate::codex::Session;
+use crate::codex::SessionSettingsUpdate;
+use crate::codex::SteerInputError;
+
+use crate::codex::spawn_review_thread;
+use crate::config::Config;
+
+use crate::mcp::auth::compute_auth_statuses;
+use crate::mcp::collect_mcp_snapshot_from_manager;
+use crate::review_prompts::resolve_review_request;
+use crate::rollout::RolloutRecorder;
+use crate::rollout::session_index;
+use crate::tasks::CompactTask;
+use crate::tasks::UndoTask;
+use crate::tasks::UserShellCommandMode;
+use crate::tasks::UserShellCommandTask;
+use crate::tasks::execute_user_shell_command;
+use codex_protocol::custom_prompts::CustomPrompt;
+use codex_protocol::protocol::CodexErrorInfo;
+use codex_protocol::protocol::ErrorEvent;
+use codex_protocol::protocol::Event;
+use codex_protocol::protocol::EventMsg;
+use codex_protocol::protocol::ListCustomPromptsResponseEvent;
+use codex_protocol::protocol::ListSkillsResponseEvent;
+use codex_protocol::protocol::McpServerRefreshConfig;
+use codex_protocol::protocol::Op;
+use codex_protocol::protocol::ReviewDecision;
+use codex_protocol::protocol::ReviewRequest;
+use codex_protocol::protocol::RolloutItem;
+use codex_protocol::protocol::SkillsListEntry;
+use codex_protocol::protocol::ThreadNameUpdatedEvent;
+use codex_protocol::protocol::ThreadRolledBackEvent;
+use codex_protocol::protocol::TurnAbortReason;
+use codex_protocol::protocol::WarningEvent;
+use codex_protocol::request_permissions::RequestPermissionsResponse;
+use codex_protocol::request_user_input::RequestUserInputResponse;
+
+use crate::context_manager::is_user_turn_boundary;
+use codex_protocol::config_types::CollaborationMode;
+use codex_protocol::config_types::ModeKind;
+use codex_protocol::config_types::Settings;
+use codex_protocol::dynamic_tools::DynamicToolResponse;
+use codex_protocol::mcp::RequestId as ProtocolRequestId;
+use codex_protocol::user_input::UserInput;
+use codex_rmcp_client::ElicitationAction;
+use codex_rmcp_client::ElicitationResponse;
+use serde_json::Value;
+use std::path::PathBuf;
+use std::sync::Arc;
+use tracing::info;
+use tracing::warn;
+
+pub async fn interrupt(sess: &Arc<Session>) {
+    sess.interrupt_task().await;
+}
+
+pub async fn clean_background_terminals(sess: &Arc<Session>) {
+    sess.close_unified_exec_processes().await;
+}
+
+pub async fn override_turn_context(sess: &Session, sub_id: String, updates: SessionSettingsUpdate) {
+    if let Err(err) = sess.update_settings(updates).await {
+        sess.send_event_raw(Event {
+            id: sub_id,
+            msg: EventMsg::Error(ErrorEvent {
+                message: err.to_string(),
+                codex_error_info: Some(CodexErrorInfo::BadRequest),
+            }),
+        })
+        .await;
+    }
+}
+
+pub async fn user_input_or_turn(sess: &Arc<Session>, sub_id: String, op: Op) {
+    let (items, updates) = match op {
+        Op::UserTurn {
+            cwd,
+            approval_policy,
+            sandbox_policy,
+            model,
+            effort,
+            summary,
+            service_tier,
+            final_output_json_schema,
+            items,
+            collaboration_mode,
+            personality,
+        } => {
+            let collaboration_mode = collaboration_mode.or_else(|| {
+                Some(CollaborationMode {
+                    mode: ModeKind::Default,
+                    settings: Settings {
+                        model: model.clone(),
+                        reasoning_effort: effort,
+                        developer_instructions: None,
+                    },
+                })
+            });
+            (
+                items,
+                SessionSettingsUpdate {
+                    cwd: Some(cwd),
+                    approval_policy: Some(approval_policy),
+                    approvals_reviewer: None,
+                    sandbox_policy: Some(sandbox_policy),
+                    windows_sandbox_level: None,
+                    collaboration_mode,
+                    reasoning_summary: summary,
+                    service_tier,
+                    final_output_json_schema: Some(final_output_json_schema),
+                    personality,
+                    app_server_client_name: None,
+                },
+            )
+        }
+        Op::UserInput {
+            items,
+            final_output_json_schema,
+        } => (
+            items,
+            SessionSettingsUpdate {
+                final_output_json_schema: Some(final_output_json_schema),
+                ..Default::default()
+            },
+        ),
+        _ => unreachable!(),
+    };
+
+    let Ok(current_context) = sess.new_turn_with_sub_id(sub_id, updates).await else {
+        // new_turn_with_sub_id already emits the error event.
+        return;
+    };
+    sess.maybe_emit_unknown_model_warning_for_turn(current_context.as_ref())
+        .await;
+    current_context.session_telemetry.user_prompt(&items);
+
+    // Attempt to inject input into current task.
+    if let Err(SteerInputError::NoActiveTurn(items)) =
+        sess.steer_input(items, /*expected_turn_id*/ None).await
+    {
+        sess.refresh_mcp_servers_if_requested(&current_context)
+            .await;
+        sess.spawn_task(
+            Arc::clone(&current_context),
+            items,
+            crate::tasks::RegularTask::new(),
+        )
+        .await;
+    }
+}
+
+pub async fn run_user_shell_command(sess: &Arc<Session>, sub_id: String, command: String) {
+    if let Some((turn_context, cancellation_token)) =
+        sess.active_turn_context_and_cancellation_token().await
+    {
+        let session = Arc::clone(sess);
+        tokio::spawn(async move {
+            execute_user_shell_command(
+                session,
+                turn_context,
+                command,
+                cancellation_token,
+                UserShellCommandMode::ActiveTurnAuxiliary,
+            )
+            .await;
+        });
+        return;
+    }
+
+    let turn_context = sess.new_default_turn_with_sub_id(sub_id).await;
+    sess.spawn_task(
+        Arc::clone(&turn_context),
+        Vec::new(),
+        UserShellCommandTask::new(command),
+    )
+    .await;
+}
+
+pub async fn resolve_elicitation(
+    sess: &Arc<Session>,
+    server_name: String,
+    request_id: ProtocolRequestId,
+    decision: codex_protocol::approvals::ElicitationAction,
+    content: Option<Value>,
+    meta: Option<Value>,
+) {
+    let action = match decision {
+        codex_protocol::approvals::ElicitationAction::Accept => ElicitationAction::Accept,
+        codex_protocol::approvals::ElicitationAction::Decline => ElicitationAction::Decline,
+        codex_protocol::approvals::ElicitationAction::Cancel => ElicitationAction::Cancel,
+    };
+    let content = match action {
+        // Preserve the legacy fallback for clients that only send an action.
+        ElicitationAction::Accept => Some(content.unwrap_or_else(|| serde_json::json!({}))),
+        ElicitationAction::Decline | ElicitationAction::Cancel => None,
+    };
+    let response = ElicitationResponse {
+        action,
+        content,
+        meta,
+    };
+    let request_id = match request_id {
+        ProtocolRequestId::String(value) => {
+            rmcp::model::NumberOrString::String(std::sync::Arc::from(value))
+        }
+        ProtocolRequestId::Integer(value) => rmcp::model::NumberOrString::Number(value),
+    };
+    if let Err(err) = sess
+        .resolve_elicitation(server_name, request_id, response)
+        .await
+    {
+        warn!(
+            error = %err,
+            "failed to resolve elicitation request in session"
+        );
+    }
+}
+
+/// Propagate a user's exec approval decision to the session.
+/// Also optionally applies an execpolicy amendment.
+pub async fn exec_approval(
+    sess: &Arc<Session>,
+    approval_id: String,
+    turn_id: Option<String>,
+    decision: ReviewDecision,
+) {
+    let event_turn_id = turn_id.unwrap_or_else(|| approval_id.clone());
+    if let ReviewDecision::ApprovedExecpolicyAmendment {
+        proposed_execpolicy_amendment,
+    } = &decision
+    {
+        match sess
+            .persist_execpolicy_amendment(proposed_execpolicy_amendment)
+            .await
+        {
+            Ok(()) => {
+                sess.record_execpolicy_amendment_message(
+                    &event_turn_id,
+                    proposed_execpolicy_amendment,
+                )
+                .await;
+            }
+            Err(err) => {
+                let message = format!("Failed to apply execpolicy amendment: {err}");
+                tracing::warn!("{message}");
+                let warning = EventMsg::Warning(WarningEvent { message });
+                sess.send_event_raw(Event {
+                    id: event_turn_id.clone(),
+                    msg: warning,
+                })
+                .await;
+            }
+        }
+    }
+    match decision {
+        ReviewDecision::Abort => {
+            sess.interrupt_task().await;
+        }
+        other => sess.notify_approval(&approval_id, other).await,
+    }
+}
+
+pub async fn patch_approval(sess: &Arc<Session>, id: String, decision: ReviewDecision) {
+    match decision {
+        ReviewDecision::Abort => {
+            sess.interrupt_task().await;
+        }
+        other => sess.notify_approval(&id, other).await,
+    }
+}
+
+pub async fn request_user_input_response(
+    sess: &Arc<Session>,
+    id: String,
+    response: RequestUserInputResponse,
+) {
+    sess.notify_user_input_response(&id, response).await;
+}
+
+pub async fn request_permissions_response(
+    sess: &Arc<Session>,
+    id: String,
+    response: RequestPermissionsResponse,
+) {
+    sess.notify_request_permissions_response(&id, response)
+        .await;
+}
+
+pub async fn dynamic_tool_response(sess: &Arc<Session>, id: String, response: DynamicToolResponse) {
+    sess.notify_dynamic_tool_response(&id, response).await;
+}
+
+pub async fn add_to_history(sess: &Arc<Session>, config: &Arc<Config>, text: String) {
+    let id = sess.conversation_id;
+    let config = Arc::clone(config);
+    tokio::spawn(async move {
+        if let Err(e) = crate::message_history::append_entry(&text, &id, &config).await {
+            warn!("failed to append to message history: {e}");
+        }
+    });
+}
+
+pub async fn get_history_entry_request(
+    sess: &Arc<Session>,
+    config: &Arc<Config>,
+    sub_id: String,
+    offset: usize,
+    log_id: u64,
+) {
+    let config = Arc::clone(config);
+    let sess_clone = Arc::clone(sess);
+
+    tokio::spawn(async move {
+        // Run lookup in blocking thread because it does file IO + locking.
+        let entry_opt = tokio::task::spawn_blocking(move || {
+            crate::message_history::lookup(log_id, offset, &config)
+        })
+        .await
+        .unwrap_or(None);
+
+        let event = Event {
+            id: sub_id,
+            msg: EventMsg::GetHistoryEntryResponse(crate::protocol::GetHistoryEntryResponseEvent {
+                offset,
+                log_id,
+                entry: entry_opt.map(|e| codex_protocol::message_history::HistoryEntry {
+                    conversation_id: e.session_id,
+                    ts: e.ts,
+                    text: e.text,
+                }),
+            }),
+        };
+
+        sess_clone.send_event_raw(event).await;
+    });
+}
+
+pub async fn refresh_mcp_servers(sess: &Arc<Session>, refresh_config: McpServerRefreshConfig) {
+    let mut guard = sess.pending_mcp_server_refresh_config.lock().await;
+    *guard = Some(refresh_config);
+}
+
+pub async fn reload_user_config(sess: &Arc<Session>) {
+    sess.reload_user_config_layer().await;
+}
+
+pub async fn list_mcp_tools(sess: &Session, config: &Arc<Config>, sub_id: String) {
+    let mcp_connection_manager = sess.services.mcp_connection_manager.read().await;
+    let auth = sess.services.auth_manager.auth().await;
+    let mcp_servers = sess
+        .services
+        .mcp_manager
+        .effective_servers(config, auth.as_ref());
+    let snapshot = collect_mcp_snapshot_from_manager(
+        &mcp_connection_manager,
+        compute_auth_statuses(mcp_servers.iter(), config.mcp_oauth_credentials_store_mode).await,
+    )
+    .await;
+    let event = Event {
+        id: sub_id,
+        msg: EventMsg::McpListToolsResponse(snapshot),
+    };
+    sess.send_event_raw(event).await;
+}
+
+pub async fn list_custom_prompts(sess: &Session, sub_id: String) {
+    let custom_prompts: Vec<CustomPrompt> =
+        if let Some(dir) = crate::custom_prompts::default_prompts_dir() {
+            crate::custom_prompts::discover_prompts_in(&dir).await
+        } else {
+            Vec::new()
+        };
+
+    let event = Event {
+        id: sub_id,
+        msg: EventMsg::ListCustomPromptsResponse(ListCustomPromptsResponseEvent { custom_prompts }),
+    };
+    sess.send_event_raw(event).await;
+}
+
+pub async fn list_skills(sess: &Session, sub_id: String, cwds: Vec<PathBuf>, force_reload: bool) {
+    let (cwds, session_source) = if cwds.is_empty() {
+        let state = sess.state.lock().await;
+        (
+            vec![state.session_configuration.cwd.clone()],
+            state.session_configuration.session_source.clone(),
+        )
+    } else {
+        let state = sess.state.lock().await;
+        (cwds, state.session_configuration.session_source.clone())
+    };
+
+    let skills_manager = &sess.services.skills_manager;
+    let mut skills = Vec::new();
+    for cwd in cwds {
+        let outcome = crate::skills::filter_skill_load_outcome_for_session_source(
+            skills_manager.skills_for_cwd(&cwd, force_reload).await,
+            &session_source,
+        );
+        let errors = super::errors_to_info(&outcome.errors);
+        let skills_metadata = super::skills_to_info(&outcome.skills, &outcome.disabled_paths);
+        skills.push(SkillsListEntry {
+            cwd,
+            skills: skills_metadata,
+            errors,
+        });
+    }
+
+    let event = Event {
+        id: sub_id,
+        msg: EventMsg::ListSkillsResponse(ListSkillsResponseEvent { skills }),
+    };
+    sess.send_event_raw(event).await;
+}
+
+pub async fn undo(sess: &Arc<Session>, sub_id: String) {
+    let turn_context = sess.new_default_turn_with_sub_id(sub_id).await;
+    sess.spawn_task(turn_context, Vec::new(), UndoTask::new())
+        .await;
+}
+
+pub async fn compact(sess: &Arc<Session>, sub_id: String) {
+    let turn_context = sess.new_default_turn_with_sub_id(sub_id).await;
+
+    sess.spawn_task(
+        Arc::clone(&turn_context),
+        vec![UserInput::Text {
+            text: turn_context.compact_prompt().to_string(),
+            // Compaction prompt is synthesized; no UI element ranges to preserve.
+            text_elements: Vec::new(),
+        }],
+        CompactTask,
+    )
+    .await;
+}
+
+pub async fn drop_memories(sess: &Arc<Session>, config: &Arc<Config>, sub_id: String) {
+    let mut errors = Vec::new();
+
+    if let Some(state_db) = sess.services.state_db.as_deref() {
+        if let Err(err) = state_db.clear_memory_data().await {
+            errors.push(format!("failed clearing memory rows from state db: {err}"));
+        }
+    } else {
+        errors.push("state db unavailable; memory rows were not cleared".to_string());
+    }
+
+    let memory_root = crate::memories::memory_root(&config.codex_home);
+    if let Err(err) = crate::memories::clear_memory_root_contents(&memory_root).await {
+        errors.push(format!(
+            "failed clearing memory directory {}: {err}",
+            memory_root.display()
+        ));
+    }
+
+    if errors.is_empty() {
+        sess.send_event_raw(Event {
+            id: sub_id,
+            msg: EventMsg::Warning(WarningEvent {
+                message: format!(
+                    "Dropped memories at {} and cleared memory rows from state db.",
+                    memory_root.display()
+                ),
+            }),
+        })
+        .await;
+        return;
+    }
+
+    sess.send_event_raw(Event {
+        id: sub_id,
+        msg: EventMsg::Error(ErrorEvent {
+            message: format!("Memory drop completed with errors: {}", errors.join("; ")),
+            codex_error_info: Some(CodexErrorInfo::Other),
+        }),
+    })
+    .await;
+}
+
+pub async fn update_memories(sess: &Arc<Session>, config: &Arc<Config>, sub_id: String) {
+    let session_source = {
+        let state = sess.state.lock().await;
+        state.session_configuration.session_source.clone()
+    };
+
+    crate::memories::start_memories_startup_task(sess, Arc::clone(config), &session_source);
+
+    sess.send_event_raw(Event {
+        id: sub_id.clone(),
+        msg: EventMsg::Warning(WarningEvent {
+            message: "Memory update triggered.".to_string(),
+        }),
+    })
+    .await;
+}
+
+pub async fn thread_rollback(sess: &Arc<Session>, sub_id: String, num_turns: u32) {
+    if num_turns == 0 {
+        sess.send_event_raw(Event {
+            id: sub_id,
+            msg: EventMsg::Error(ErrorEvent {
+                message: "num_turns must be >= 1".to_string(),
+                codex_error_info: Some(CodexErrorInfo::ThreadRollbackFailed),
+            }),
+        })
+        .await;
+        return;
+    }
+
+    let has_active_turn = { sess.active_turn.lock().await.is_some() };
+    if has_active_turn {
+        sess.send_event_raw(Event {
+            id: sub_id,
+            msg: EventMsg::Error(ErrorEvent {
+                message: "Cannot rollback while a turn is in progress.".to_string(),
+                codex_error_info: Some(CodexErrorInfo::ThreadRollbackFailed),
+            }),
+        })
+        .await;
+        return;
+    }
+
+    let turn_context = sess.new_default_turn_with_sub_id(sub_id).await;
+    let rollout_path = {
+        let recorder = {
+            let guard = sess.services.rollout.lock().await;
+            guard.clone()
+        };
+        let Some(recorder) = recorder else {
+            sess.send_event_raw(Event {
+                id: turn_context.sub_id.clone(),
+                msg: EventMsg::Error(ErrorEvent {
+                    message: "thread rollback requires a persisted rollout path".to_string(),
+                    codex_error_info: Some(CodexErrorInfo::ThreadRollbackFailed),
+                }),
+            })
+            .await;
+            return;
+        };
+        recorder.rollout_path().to_path_buf()
+    };
+    if let Some(recorder) = {
+        let guard = sess.services.rollout.lock().await;
+        guard.clone()
+    } && let Err(err) = recorder.flush().await
+    {
+        sess.send_event_raw(Event {
+            id: turn_context.sub_id.clone(),
+            msg: EventMsg::Error(ErrorEvent {
+                message: format!(
+                    "failed to flush rollout `{}` for rollback replay: {err}",
+                    rollout_path.display()
+                ),
+                codex_error_info: Some(CodexErrorInfo::ThreadRollbackFailed),
+            }),
+        })
+        .await;
+        return;
+    }
+
+    let initial_history = match RolloutRecorder::get_rollout_history(rollout_path.as_path()).await {
+        Ok(history) => history,
+        Err(err) => {
+            sess.send_event_raw(Event {
+                id: turn_context.sub_id.clone(),
+                msg: EventMsg::Error(ErrorEvent {
+                    message: format!(
+                        "failed to load rollout `{}` for rollback replay: {err}",
+                        rollout_path.display()
+                    ),
+                    codex_error_info: Some(CodexErrorInfo::ThreadRollbackFailed),
+                }),
+            })
+            .await;
+            return;
+        }
+    };
+
+    let rollback_event = ThreadRolledBackEvent { num_turns };
+    let rollback_msg = EventMsg::ThreadRolledBack(rollback_event.clone());
+    let replay_items = initial_history
+        .get_rollout_items()
+        .into_iter()
+        .chain(std::iter::once(RolloutItem::EventMsg(rollback_msg.clone())))
+        .collect::<Vec<_>>();
+    sess.persist_rollout_items(&[RolloutItem::EventMsg(rollback_msg.clone())])
+        .await;
+    sess.flush_rollout().await;
+    sess.apply_rollout_reconstruction(turn_context.as_ref(), replay_items.as_slice())
+        .await;
+    sess.recompute_token_usage(turn_context.as_ref()).await;
+
+    sess.deliver_event_raw(Event {
+        id: turn_context.sub_id.clone(),
+        msg: rollback_msg,
+    })
+    .await;
+}
+
+/// Persists the thread name in the session index, updates in-memory state, and emits
+/// a `ThreadNameUpdated` event on success.
+///
+/// This appends the name to `CODEX_HOME/sessions_index.jsonl` via `session_index::append_thread_name` for the
+/// current `thread_id`, then updates `SessionConfiguration::thread_name`.
+///
+/// Returns an error event if the name is empty or session persistence is disabled.
+pub async fn set_thread_name(sess: &Arc<Session>, sub_id: String, name: String) {
+    let Some(name) = crate::util::normalize_thread_name(&name) else {
+        let event = Event {
+            id: sub_id,
+            msg: EventMsg::Error(ErrorEvent {
+                message: "Thread name cannot be empty.".to_string(),
+                codex_error_info: Some(CodexErrorInfo::BadRequest),
+            }),
+        };
+        sess.send_event_raw(event).await;
+        return;
+    };
+
+    let persistence_enabled = {
+        let rollout = sess.services.rollout.lock().await;
+        rollout.is_some()
+    };
+    if !persistence_enabled {
+        let event = Event {
+            id: sub_id,
+            msg: EventMsg::Error(ErrorEvent {
+                message: "Session persistence is disabled; cannot rename thread.".to_string(),
+                codex_error_info: Some(CodexErrorInfo::Other),
+            }),
+        };
+        sess.send_event_raw(event).await;
+        return;
+    };
+
+    let codex_home = sess.codex_home().await;
+    if let Err(e) =
+        session_index::append_thread_name(&codex_home, sess.conversation_id, &name).await
+    {
+        let event = Event {
+            id: sub_id,
+            msg: EventMsg::Error(ErrorEvent {
+                message: format!("Failed to set thread name: {e}"),
+                codex_error_info: Some(CodexErrorInfo::Other),
+            }),
+        };
+        sess.send_event_raw(event).await;
+        return;
+    }
+
+    {
+        let mut state = sess.state.lock().await;
+        state.session_configuration.thread_name = Some(name.clone());
+    }
+
+    sess.send_event_raw(Event {
+        id: sub_id,
+        msg: EventMsg::ThreadNameUpdated(ThreadNameUpdatedEvent {
+            thread_id: sess.conversation_id,
+            thread_name: Some(name),
+        }),
+    })
+    .await;
+}
+
+pub async fn shutdown(sess: &Arc<Session>, sub_id: String) -> bool {
+    sess.abort_all_tasks(TurnAbortReason::Interrupted).await;
+    let _ = sess.conversation.shutdown().await;
+    sess.services
+        .unified_exec_manager
+        .terminate_all_processes()
+        .await;
+    sess.guardian_review_session.shutdown().await;
+    info!("Shutting down Codex instance");
+    let history = sess.clone_history().await;
+    let turn_count = history
+        .raw_items()
+        .iter()
+        .filter(|item| is_user_turn_boundary(item))
+        .count();
+    sess.services.session_telemetry.counter(
+        "codex.conversation.turn.count",
+        i64::try_from(turn_count).unwrap_or(0),
+        &[],
+    );
+
+    // Gracefully flush and shutdown rollout recorder on session end so tests
+    // that inspect the rollout file do not race with the background writer.
+    let recorder_opt = {
+        let mut guard = sess.services.rollout.lock().await;
+        guard.take()
+    };
+    if let Some(rec) = recorder_opt
+        && let Err(e) = rec.shutdown().await
+    {
+        warn!("failed to shutdown rollout recorder: {e}");
+        let event = Event {
+            id: sub_id.clone(),
+            msg: EventMsg::Error(ErrorEvent {
+                message: "Failed to shutdown rollout recorder".to_string(),
+                codex_error_info: Some(CodexErrorInfo::Other),
+            }),
+        };
+        sess.send_event_raw(event).await;
+    }
+
+    let event = Event {
+        id: sub_id,
+        msg: EventMsg::ShutdownComplete,
+    };
+    sess.send_event_raw(event).await;
+    true
+}
+
+pub async fn review(
+    sess: &Arc<Session>,
+    config: &Arc<Config>,
+    sub_id: String,
+    review_request: ReviewRequest,
+) {
+    let turn_context = sess.new_default_turn_with_sub_id(sub_id.clone()).await;
+    sess.maybe_emit_unknown_model_warning_for_turn(turn_context.as_ref())
+        .await;
+    sess.refresh_mcp_servers_if_requested(&turn_context).await;
+    match resolve_review_request(review_request, turn_context.cwd.as_path()) {
+        Ok(resolved) => {
+            spawn_review_thread(
+                Arc::clone(sess),
+                Arc::clone(config),
+                turn_context.clone(),
+                sub_id,
+                resolved,
+            )
+            .await;
+        }
+        Err(err) => {
+            let event = Event {
+                id: sub_id,
+                msg: EventMsg::Error(ErrorEvent {
+                    message: err.to_string(),
+                    codex_error_info: Some(CodexErrorInfo::Other),
+                }),
+            };
+            sess.send_event(&turn_context, event.msg).await;
+        }
+    }
+}

codex-rs/core/src/codex_tests.rs

@@ -2465,7 +2465,7 @@ pub(crate) async fn make_session_and_context() -> (Session, TurnContext) {
         true,
     ));
     let network_approval = Arc::new(NetworkApprovalService::default());
-    let environment = Arc::new(codex_environment::Environment);
+    let environment = Arc::new(codex_environment::Environment::default());
 
     let file_watcher = Arc::new(FileWatcher::noop());
     let services = SessionServices {
@@ -3259,7 +3259,7 @@ pub(crate) async fn make_session_and_context_with_dynamic_tools_and_rx(
         true,
     ));
     let network_approval = Arc::new(NetworkApprovalService::default());
-    let environment = Arc::new(codex_environment::Environment);
+    let environment = Arc::new(codex_environment::Environment::default());
 
     let file_watcher = Arc::new(FileWatcher::noop());
     let services = SessionServices {

codex-rs/core/src/config/config_tests.rs

@@ -4328,6 +4328,8 @@ fn test_precedence_fixture_with_o3_profile() -> std::io::Result<()> {
             web_search_mode: Constrained::allow_any(WebSearchMode::Cached),
             web_search_config: None,
             use_experimental_unified_exec_tool: !cfg!(windows),
+            experimental_unified_exec_exec_server_websocket_url: None,
+            experimental_unified_exec_exec_server_workspace_root: None,
             background_terminal_max_timeout: DEFAULT_MAX_BACKGROUND_TERMINAL_TIMEOUT_MS,
             ghost_snapshot: GhostSnapshotConfig::default(),
             features: Features::with_defaults().into(),
@@ -4469,6 +4471,8 @@ fn test_precedence_fixture_with_gpt3_profile() -> std::io::Result<()> {
         web_search_mode: Constrained::allow_any(WebSearchMode::Cached),
         web_search_config: None,
         use_experimental_unified_exec_tool: !cfg!(windows),
+        experimental_unified_exec_exec_server_websocket_url: None,
+        experimental_unified_exec_exec_server_workspace_root: None,
         background_terminal_max_timeout: DEFAULT_MAX_BACKGROUND_TERMINAL_TIMEOUT_MS,
         ghost_snapshot: GhostSnapshotConfig::default(),
         features: Features::with_defaults().into(),
@@ -4608,6 +4612,8 @@ fn test_precedence_fixture_with_zdr_profile() -> std::io::Result<()> {
         web_search_mode: Constrained::allow_any(WebSearchMode::Cached),
         web_search_config: None,
         use_experimental_unified_exec_tool: !cfg!(windows),
+        experimental_unified_exec_exec_server_websocket_url: None,
+        experimental_unified_exec_exec_server_workspace_root: None,
         background_terminal_max_timeout: DEFAULT_MAX_BACKGROUND_TERMINAL_TIMEOUT_MS,
         ghost_snapshot: GhostSnapshotConfig::default(),
         features: Features::with_defaults().into(),
@@ -4733,6 +4739,8 @@ fn test_precedence_fixture_with_gpt5_profile() -> std::io::Result<()> {
         web_search_mode: Constrained::allow_any(WebSearchMode::Cached),
         web_search_config: None,
         use_experimental_unified_exec_tool: !cfg!(windows),
+        experimental_unified_exec_exec_server_websocket_url: None,
+        experimental_unified_exec_exec_server_workspace_root: None,
         background_terminal_max_timeout: DEFAULT_MAX_BACKGROUND_TERMINAL_TIMEOUT_MS,
         ghost_snapshot: GhostSnapshotConfig::default(),
         features: Features::with_defaults().into(),

codex-rs/core/src/config/mod.rs

@@ -539,6 +539,14 @@ pub struct Config {
     /// If set to `true`, used only the experimental unified exec tool.
     pub use_experimental_unified_exec_tool: bool,
 
+    /// When set, connect unified-exec process launches to an existing remote
+    /// `codex-exec-server` websocket endpoint.
+    pub experimental_unified_exec_exec_server_websocket_url: Option<String>,
+
+    /// When set, map local session cwd to this executor-visible workspace root
+    /// for remote unified-exec process launches.
+    pub experimental_unified_exec_exec_server_workspace_root: Option<AbsolutePathBuf>,
+
     /// Maximum poll window for background terminal output (`write_stdin`), in milliseconds.
     /// Default: `300000` (5 minutes).
     pub background_terminal_max_timeout: u64,
@@ -1325,6 +1333,13 @@ pub struct ConfigToml {
     /// Default: `300000` (5 minutes).
     pub background_terminal_max_timeout: Option<u64>,
 
+    /// Optional websocket URL for connecting to an existing `codex-exec-server`.
+    pub experimental_unified_exec_exec_server_websocket_url: Option<String>,
+
+    /// Optional absolute path to the executor-visible workspace root that
+    /// corresponds to the local session cwd.
+    pub experimental_unified_exec_exec_server_workspace_root: Option<AbsolutePathBuf>,
+
     /// Optional absolute path to the Node runtime used by `js_repl`.
     pub js_repl_node_path: Option<AbsolutePathBuf>,
 
@@ -2474,6 +2489,20 @@ impl Config {
 
         let include_apply_patch_tool_flag = features.enabled(Feature::ApplyPatchFreeform);
         let use_experimental_unified_exec_tool = features.enabled(Feature::UnifiedExec);
+        let experimental_unified_exec_exec_server_websocket_url = cfg
+            .experimental_unified_exec_exec_server_websocket_url
+            .clone()
+            .and_then(|value: String| {
+                let trimmed = value.trim();
+                if trimmed.is_empty() {
+                    None
+                } else {
+                    Some(trimmed.to_string())
+                }
+            });
+        let experimental_unified_exec_exec_server_workspace_root = cfg
+            .experimental_unified_exec_exec_server_workspace_root
+            .clone();
 
         let forced_chatgpt_workspace_id =
             cfg.forced_chatgpt_workspace_id.as_ref().and_then(|value| {
@@ -2768,6 +2797,8 @@ impl Config {
             web_search_mode: constrained_web_search_mode.value,
             web_search_config,
             use_experimental_unified_exec_tool,
+            experimental_unified_exec_exec_server_websocket_url,
+            experimental_unified_exec_exec_server_workspace_root,
             background_terminal_max_timeout,
             ghost_snapshot,
             features,

codex-rs/core/src/connectors.rs

@@ -217,6 +217,7 @@ pub async fn list_accessible_connectors_from_mcp_tools_with_options_and_status(
     };
 
     let (mcp_connection_manager, cancel_token) = McpConnectionManager::new(
+        String::new(),
         &mcp_servers,
         config.mcp_oauth_credentials_store_mode,
         auth_status_entries,

codex-rs/core/src/lib.rs

@@ -14,6 +14,8 @@ pub mod auth;
 mod auth_env_telemetry;
 mod client;
 mod client_common;
+#[cfg(test)]
+mod client_tools;
 pub mod codex;
 mod realtime_context;
 mod realtime_conversation;
@@ -55,9 +57,9 @@ mod network_policy_decision;
 pub mod network_proxy_loader;
 mod original_image_detail;
 mod packages;
+pub use mcp::types::SandboxState;
 pub use mcp_connection_manager::MCP_SANDBOX_STATE_CAPABILITY;
 pub use mcp_connection_manager::MCP_SANDBOX_STATE_METHOD;
-pub use mcp_connection_manager::SandboxState;
 pub use text_encoding::bytes_to_string_smart;
 mod mcp_tool_call;
 mod memories;

codex-rs/core/src/mcp/config.rs

@@ -0,0 +1,117 @@
+use std::collections::HashMap;
+use std::env;
+use std::time::Duration;
+
+use crate::CodexAuth;
+use crate::config::Config;
+use crate::config::types::McpServerConfig;
+use crate::config::types::McpServerTransportConfig;
+
+use super::CODEX_APPS_MCP_SERVER_NAME;
+
+pub(crate) const CODEX_CONNECTORS_TOKEN_ENV_VAR: &str = "CODEX_CONNECTORS_TOKEN";
+
+fn codex_apps_mcp_bearer_token_env_var() -> Option<String> {
+    match env::var(CODEX_CONNECTORS_TOKEN_ENV_VAR) {
+        Ok(value) if !value.trim().is_empty() => Some(CODEX_CONNECTORS_TOKEN_ENV_VAR.to_string()),
+        Ok(_) => None,
+        Err(env::VarError::NotPresent) => None,
+        Err(env::VarError::NotUnicode(_)) => Some(CODEX_CONNECTORS_TOKEN_ENV_VAR.to_string()),
+    }
+}
+
+fn codex_apps_mcp_bearer_token(auth: Option<&CodexAuth>) -> Option<String> {
+    let token = auth.and_then(|auth| auth.get_token().ok())?;
+    let token = token.trim();
+    if token.is_empty() {
+        None
+    } else {
+        Some(token.to_string())
+    }
+}
+
+fn codex_apps_mcp_http_headers(auth: Option<&CodexAuth>) -> Option<HashMap<String, String>> {
+    let mut headers = HashMap::new();
+    if let Some(token) = codex_apps_mcp_bearer_token(auth) {
+        headers.insert("Authorization".to_string(), format!("Bearer {token}"));
+    }
+    if let Some(account_id) = auth.and_then(CodexAuth::get_account_id) {
+        headers.insert("ChatGPT-Account-ID".to_string(), account_id);
+    }
+    if headers.is_empty() {
+        None
+    } else {
+        Some(headers)
+    }
+}
+
+fn normalize_codex_apps_base_url(base_url: &str) -> String {
+    let mut base_url = base_url.trim_end_matches('/').to_string();
+    if (base_url.starts_with("https://chatgpt.com")
+        || base_url.starts_with("https://chat.openai.com"))
+        && !base_url.contains("/backend-api")
+    {
+        base_url = format!("{base_url}/backend-api");
+    }
+    base_url
+}
+
+pub(crate) fn codex_apps_mcp_url_for_base_url(base_url: &str) -> String {
+    let base_url = normalize_codex_apps_base_url(base_url);
+    if base_url.contains("/backend-api") {
+        format!("{base_url}/wham/apps")
+    } else if base_url.contains("/api/codex") {
+        format!("{base_url}/apps")
+    } else {
+        format!("{base_url}/api/codex/apps")
+    }
+}
+
+pub(crate) fn codex_apps_mcp_url(config: &Config) -> String {
+    codex_apps_mcp_url_for_base_url(&config.chatgpt_base_url)
+}
+
+fn codex_apps_mcp_server_config(config: &Config, auth: Option<&CodexAuth>) -> McpServerConfig {
+    let bearer_token_env_var = codex_apps_mcp_bearer_token_env_var();
+    let http_headers = if bearer_token_env_var.is_some() {
+        None
+    } else {
+        codex_apps_mcp_http_headers(auth)
+    };
+    let url = codex_apps_mcp_url(config);
+
+    McpServerConfig {
+        transport: McpServerTransportConfig::StreamableHttp {
+            url,
+            bearer_token_env_var,
+            http_headers,
+            env_http_headers: None,
+        },
+        enabled: true,
+        required: false,
+        disabled_reason: None,
+        startup_timeout_sec: Some(Duration::from_secs(30)),
+        tool_timeout_sec: None,
+        enabled_tools: None,
+        disabled_tools: None,
+        scopes: None,
+        oauth_resource: None,
+    }
+}
+
+pub(crate) fn with_codex_apps_mcp(
+    mut servers: HashMap<String, McpServerConfig>,
+    connectors_enabled: bool,
+    auth: Option<&CodexAuth>,
+    config: &Config,
+) -> HashMap<String, McpServerConfig> {
+    if connectors_enabled {
+        servers.insert(
+            CODEX_APPS_MCP_SERVER_NAME.to_string(),
+            codex_apps_mcp_server_config(config, auth),
+        );
+    } else {
+        servers.remove(CODEX_APPS_MCP_SERVER_NAME);
+    }
+    servers
+}

codex-rs/core/src/mcp/manager.rs

@@ -0,0 +1,62 @@
+use std::collections::HashMap;
+use std::sync::Arc;
+
+use crate::CodexAuth;
+use crate::config::Config;
+use crate::config::types::McpServerConfig;
+use crate::plugins::PluginsManager;
+
+use crate::mcp::ToolPluginProvenance;
+
+pub struct McpManager {
+    plugins_manager: Arc<PluginsManager>,
+}
+
+impl McpManager {
+    pub fn new(plugins_manager: Arc<PluginsManager>) -> Self {
+        Self { plugins_manager }
+    }
+
+    pub fn configured_servers(&self, config: &Config) -> HashMap<String, McpServerConfig> {
+        configured_mcp_servers(config, self.plugins_manager.as_ref())
+    }
+
+    pub fn effective_servers(
+        &self,
+        config: &Config,
+        auth: Option<&CodexAuth>,
+    ) -> HashMap<String, McpServerConfig> {
+        effective_mcp_servers(config, auth, self.plugins_manager.as_ref())
+    }
+
+    pub fn tool_plugin_provenance(&self, config: &Config) -> ToolPluginProvenance {
+        let loaded_plugins = self.plugins_manager.plugins_for_config(config);
+        ToolPluginProvenance::from_capability_summaries(loaded_plugins.capability_summaries())
+    }
+}
+
+fn configured_mcp_servers(
+    config: &Config,
+    plugins_manager: &PluginsManager,
+) -> HashMap<String, McpServerConfig> {
+    let loaded_plugins = plugins_manager.plugins_for_config(config);
+    let mut servers = config.mcp_servers.get().clone();
+    for (name, plugin_server) in loaded_plugins.effective_mcp_servers() {
+        servers.entry(name).or_insert(plugin_server);
+    }
+    servers
+}
+
+fn effective_mcp_servers(
+    config: &Config,
+    auth: Option<&CodexAuth>,
+    plugins_manager: &PluginsManager,
+) -> HashMap<String, McpServerConfig> {
+    let servers = configured_mcp_servers(config, plugins_manager);
+    crate::mcp::config::with_codex_apps_mcp(
+        servers,
+        config.features.apps_enabled_for_auth(auth),
+        auth,
+        config,
+    )
+}

codex-rs/core/src/mcp/mod.rs

@@ -1,37 +1,21 @@
 pub mod auth;
+pub mod config;
+pub mod manager;
 mod skill_dependencies;
+pub mod snapshot;
+pub mod types;
+
+pub(crate) use config::with_codex_apps_mcp;
+pub(crate) use manager::McpManager;
 pub(crate) use skill_dependencies::maybe_prompt_and_install_mcp_dependencies;
+pub(crate) use snapshot::collect_mcp_snapshot_from_manager;
+pub(crate) use types::split_qualified_tool_name;
 
 use std::collections::HashMap;
-use std::env;
-use std::path::PathBuf;
-use std::sync::Arc;
-use std::time::Duration;
 
-use async_channel::unbounded;
-use codex_protocol::mcp::Resource;
-use codex_protocol::mcp::ResourceTemplate;
-use codex_protocol::mcp::Tool;
-use codex_protocol::protocol::McpListToolsResponseEvent;
-use codex_protocol::protocol::SandboxPolicy;
-use serde_json::Value;
-
-use crate::AuthManager;
-use crate::CodexAuth;
-use crate::config::Config;
-use crate::config::types::McpServerConfig;
-use crate::config::types::McpServerTransportConfig;
-use crate::mcp::auth::compute_auth_statuses;
-use crate::mcp_connection_manager::McpConnectionManager;
-use crate::mcp_connection_manager::SandboxState;
-use crate::mcp_connection_manager::codex_apps_tools_cache_key;
 use crate::plugins::PluginCapabilitySummary;
-use crate::plugins::PluginsManager;
 
-const MCP_TOOL_NAME_PREFIX: &str = "mcp";
-const MCP_TOOL_NAME_DELIMITER: &str = "__";
 pub(crate) const CODEX_APPS_MCP_SERVER_NAME: &str = "codex_apps";
-const CODEX_CONNECTORS_TOKEN_ENV_VAR: &str = "CODEX_CONNECTORS_TOKEN";
 
 #[derive(Debug, Clone, Default, PartialEq, Eq)]
 pub struct ToolPluginProvenance {
@@ -54,7 +38,9 @@ impl ToolPluginProvenance {
             .unwrap_or(&[])
     }
 
-    fn from_capability_summaries(capability_summaries: &[PluginCapabilitySummary]) -> Self {
+    pub(crate) fn from_capability_summaries(
+        capability_summaries: &[PluginCapabilitySummary],
+    ) -> Self {
         let mut tool_plugin_provenance = Self::default();
         for plugin in capability_summaries {
             for connector_id in &plugin.app_connector_ids {
@@ -91,358 +77,6 @@ impl ToolPluginProvenance {
     }
 }
 
-fn codex_apps_mcp_bearer_token_env_var() -> Option<String> {
-    match env::var(CODEX_CONNECTORS_TOKEN_ENV_VAR) {
-        Ok(value) if !value.trim().is_empty() => Some(CODEX_CONNECTORS_TOKEN_ENV_VAR.to_string()),
-        Ok(_) => None,
-        Err(env::VarError::NotPresent) => None,
-        Err(env::VarError::NotUnicode(_)) => Some(CODEX_CONNECTORS_TOKEN_ENV_VAR.to_string()),
-    }
-}
-
-fn codex_apps_mcp_bearer_token(auth: Option<&CodexAuth>) -> Option<String> {
-    let token = auth.and_then(|auth| auth.get_token().ok())?;
-    let token = token.trim();
-    if token.is_empty() {
-        None
-    } else {
-        Some(token.to_string())
-    }
-}
-
-fn codex_apps_mcp_http_headers(auth: Option<&CodexAuth>) -> Option<HashMap<String, String>> {
-    let mut headers = HashMap::new();
-    if let Some(token) = codex_apps_mcp_bearer_token(auth) {
-        headers.insert("Authorization".to_string(), format!("Bearer {token}"));
-    }
-    if let Some(account_id) = auth.and_then(CodexAuth::get_account_id) {
-        headers.insert("ChatGPT-Account-ID".to_string(), account_id);
-    }
-    if headers.is_empty() {
-        None
-    } else {
-        Some(headers)
-    }
-}
-
-fn normalize_codex_apps_base_url(base_url: &str) -> String {
-    let mut base_url = base_url.trim_end_matches('/').to_string();
-    if (base_url.starts_with("https://chatgpt.com")
-        || base_url.starts_with("https://chat.openai.com"))
-        && !base_url.contains("/backend-api")
-    {
-        base_url = format!("{base_url}/backend-api");
-    }
-    base_url
-}
-
-fn codex_apps_mcp_url_for_base_url(base_url: &str) -> String {
-    let base_url = normalize_codex_apps_base_url(base_url);
-    if base_url.contains("/backend-api") {
-        format!("{base_url}/wham/apps")
-    } else if base_url.contains("/api/codex") {
-        format!("{base_url}/apps")
-    } else {
-        format!("{base_url}/api/codex/apps")
-    }
-}
-
-pub(crate) fn codex_apps_mcp_url(config: &Config) -> String {
-    codex_apps_mcp_url_for_base_url(&config.chatgpt_base_url)
-}
-
-fn codex_apps_mcp_server_config(config: &Config, auth: Option<&CodexAuth>) -> McpServerConfig {
-    let bearer_token_env_var = codex_apps_mcp_bearer_token_env_var();
-    let http_headers = if bearer_token_env_var.is_some() {
-        None
-    } else {
-        codex_apps_mcp_http_headers(auth)
-    };
-    let url = codex_apps_mcp_url(config);
-
-    McpServerConfig {
-        transport: McpServerTransportConfig::StreamableHttp {
-            url,
-            bearer_token_env_var,
-            http_headers,
-            env_http_headers: None,
-        },
-        enabled: true,
-        required: false,
-        disabled_reason: None,
-        startup_timeout_sec: Some(Duration::from_secs(30)),
-        tool_timeout_sec: None,
-        enabled_tools: None,
-        disabled_tools: None,
-        scopes: None,
-        oauth_resource: None,
-    }
-}
-
-pub(crate) fn with_codex_apps_mcp(
-    mut servers: HashMap<String, McpServerConfig>,
-    connectors_enabled: bool,
-    auth: Option<&CodexAuth>,
-    config: &Config,
-) -> HashMap<String, McpServerConfig> {
-    if connectors_enabled {
-        servers.insert(
-            CODEX_APPS_MCP_SERVER_NAME.to_string(),
-            codex_apps_mcp_server_config(config, auth),
-        );
-    } else {
-        servers.remove(CODEX_APPS_MCP_SERVER_NAME);
-    }
-    servers
-}
-
-pub struct McpManager {
-    plugins_manager: Arc<PluginsManager>,
-}
-
-impl McpManager {
-    pub fn new(plugins_manager: Arc<PluginsManager>) -> Self {
-        Self { plugins_manager }
-    }
-
-    pub fn configured_servers(&self, config: &Config) -> HashMap<String, McpServerConfig> {
-        configured_mcp_servers(config, self.plugins_manager.as_ref())
-    }
-
-    pub fn effective_servers(
-        &self,
-        config: &Config,
-        auth: Option<&CodexAuth>,
-    ) -> HashMap<String, McpServerConfig> {
-        effective_mcp_servers(config, auth, self.plugins_manager.as_ref())
-    }
-
-    pub fn tool_plugin_provenance(&self, config: &Config) -> ToolPluginProvenance {
-        let loaded_plugins = self.plugins_manager.plugins_for_config(config);
-        ToolPluginProvenance::from_capability_summaries(loaded_plugins.capability_summaries())
-    }
-}
-
-fn configured_mcp_servers(
-    config: &Config,
-    plugins_manager: &PluginsManager,
-) -> HashMap<String, McpServerConfig> {
-    let loaded_plugins = plugins_manager.plugins_for_config(config);
-    let mut servers = config.mcp_servers.get().clone();
-    for (name, plugin_server) in loaded_plugins.effective_mcp_servers() {
-        servers.entry(name).or_insert(plugin_server);
-    }
-    servers
-}
-
-fn effective_mcp_servers(
-    config: &Config,
-    auth: Option<&CodexAuth>,
-    plugins_manager: &PluginsManager,
-) -> HashMap<String, McpServerConfig> {
-    let servers = configured_mcp_servers(config, plugins_manager);
-    with_codex_apps_mcp(
-        servers,
-        config.features.apps_enabled_for_auth(auth),
-        auth,
-        config,
-    )
-}
-
-pub async fn collect_mcp_snapshot(config: &Config) -> McpListToolsResponseEvent {
-    let auth_manager = AuthManager::shared(
-        config.codex_home.clone(),
-        /*enable_codex_api_key_env*/ false,
-        config.cli_auth_credentials_store_mode,
-    );
-    let auth = auth_manager.auth().await;
-    let mcp_manager = McpManager::new(Arc::new(PluginsManager::new(config.codex_home.clone())));
-    let mcp_servers = mcp_manager.effective_servers(config, auth.as_ref());
-    let tool_plugin_provenance = mcp_manager.tool_plugin_provenance(config);
-    if mcp_servers.is_empty() {
-        return McpListToolsResponseEvent {
-            tools: HashMap::new(),
-            resources: HashMap::new(),
-            resource_templates: HashMap::new(),
-            auth_statuses: HashMap::new(),
-        };
-    }
-
-    let auth_status_entries =
-        compute_auth_statuses(mcp_servers.iter(), config.mcp_oauth_credentials_store_mode).await;
-
-    let (tx_event, rx_event) = unbounded();
-    drop(rx_event);
-
-    // Use ReadOnly sandbox policy for MCP snapshot collection (safest default)
-    let sandbox_state = SandboxState {
-        sandbox_policy: SandboxPolicy::new_read_only_policy(),
-        codex_linux_sandbox_exe: config.codex_linux_sandbox_exe.clone(),
-        sandbox_cwd: env::current_dir().unwrap_or_else(|_| PathBuf::from("/")),
-        use_legacy_landlock: config.features.use_legacy_landlock(),
-    };
-
-    let (mcp_connection_manager, cancel_token) = McpConnectionManager::new(
-        &mcp_servers,
-        config.mcp_oauth_credentials_store_mode,
-        auth_status_entries.clone(),
-        &config.permissions.approval_policy,
-        tx_event,
-        sandbox_state,
-        config.codex_home.clone(),
-        codex_apps_tools_cache_key(auth.as_ref()),
-        tool_plugin_provenance,
-    )
-    .await;
-
-    let snapshot =
-        collect_mcp_snapshot_from_manager(&mcp_connection_manager, auth_status_entries).await;
-
-    cancel_token.cancel();
-
-    snapshot
-}
-
-pub fn split_qualified_tool_name(qualified_name: &str) -> Option<(String, String)> {
-    let mut parts = qualified_name.split(MCP_TOOL_NAME_DELIMITER);
-    let prefix = parts.next()?;
-    if prefix != MCP_TOOL_NAME_PREFIX {
-        return None;
-    }
-    let server_name = parts.next()?;
-    let tool_name: String = parts.collect::<Vec<_>>().join(MCP_TOOL_NAME_DELIMITER);
-    if tool_name.is_empty() {
-        return None;
-    }
-    Some((server_name.to_string(), tool_name))
-}
-
-pub fn group_tools_by_server(
-    tools: &HashMap<String, Tool>,
-) -> HashMap<String, HashMap<String, Tool>> {
-    let mut grouped = HashMap::new();
-    for (qualified_name, tool) in tools {
-        if let Some((server_name, tool_name)) = split_qualified_tool_name(qualified_name) {
-            grouped
-                .entry(server_name)
-                .or_insert_with(HashMap::new)
-                .insert(tool_name, tool.clone());
-        }
-    }
-    grouped
-}
-
-pub(crate) async fn collect_mcp_snapshot_from_manager(
-    mcp_connection_manager: &McpConnectionManager,
-    auth_status_entries: HashMap<String, crate::mcp::auth::McpAuthStatusEntry>,
-) -> McpListToolsResponseEvent {
-    let (tools, resources, resource_templates) = tokio::join!(
-        mcp_connection_manager.list_all_tools(),
-        mcp_connection_manager.list_all_resources(),
-        mcp_connection_manager.list_all_resource_templates(),
-    );
-
-    let auth_statuses = auth_status_entries
-        .iter()
-        .map(|(name, entry)| (name.clone(), entry.auth_status))
-        .collect();
-
-    let tools = tools
-        .into_iter()
-        .filter_map(|(name, tool)| match serde_json::to_value(tool.tool) {
-            Ok(value) => match Tool::from_mcp_value(value) {
-                Ok(tool) => Some((name, tool)),
-                Err(err) => {
-                    tracing::warn!("Failed to convert MCP tool '{name}': {err}");
-                    None
-                }
-            },
-            Err(err) => {
-                tracing::warn!("Failed to serialize MCP tool '{name}': {err}");
-                None
-            }
-        })
-        .collect();
-
-    let resources = resources
-        .into_iter()
-        .map(|(name, resources)| {
-            let resources = resources
-                .into_iter()
-                .filter_map(|resource| match serde_json::to_value(resource) {
-                    Ok(value) => match Resource::from_mcp_value(value.clone()) {
-                        Ok(resource) => Some(resource),
-                        Err(err) => {
-                            let (uri, resource_name) = match value {
-                                Value::Object(obj) => (
-                                    obj.get("uri")
-                                        .and_then(|v| v.as_str().map(ToString::to_string)),
-                                    obj.get("name")
-                                        .and_then(|v| v.as_str().map(ToString::to_string)),
-                                ),
-                                _ => (None, None),
-                            };
-
-                            tracing::warn!(
-                                "Failed to convert MCP resource (uri={uri:?}, name={resource_name:?}): {err}"
-                            );
-                            None
-                        }
-                    },
-                    Err(err) => {
-                        tracing::warn!("Failed to serialize MCP resource: {err}");
-                        None
-                    }
-                })
-                .collect::<Vec<_>>();
-            (name, resources)
-        })
-        .collect();
-
-    let resource_templates = resource_templates
-        .into_iter()
-        .map(|(name, templates)| {
-            let templates = templates
-                .into_iter()
-                .filter_map(|template| match serde_json::to_value(template) {
-                    Ok(value) => match ResourceTemplate::from_mcp_value(value.clone()) {
-                        Ok(template) => Some(template),
-                        Err(err) => {
-                            let (uri_template, template_name) = match value {
-                                Value::Object(obj) => (
-                                    obj.get("uriTemplate")
-                                        .or_else(|| obj.get("uri_template"))
-                                        .and_then(|v| v.as_str().map(ToString::to_string)),
-                                    obj.get("name")
-                                        .and_then(|v| v.as_str().map(ToString::to_string)),
-                                ),
-                                _ => (None, None),
-                            };
-
-                            tracing::warn!(
-                                "Failed to convert MCP resource template (uri_template={uri_template:?}, name={template_name:?}): {err}"
-                            );
-                            None
-                        }
-                    },
-                    Err(err) => {
-                        tracing::warn!("Failed to serialize MCP resource template: {err}");
-                        None
-                    }
-                })
-                .collect::<Vec<_>>();
-            (name, templates)
-        })
-        .collect();
-
-    McpListToolsResponseEvent {
-        tools,
-        resources,
-        resource_templates,
-        auth_statuses,
-    }
-}
-
 #[cfg(test)]
 #[path = "mod_tests.rs"]
 mod tests;

codex-rs/core/src/mcp/mod_tests.rs

@@ -1,12 +1,17 @@
 use super::*;
 use crate::config::CONFIG_TOML_FILE;
 use crate::config::ConfigBuilder;
+use crate::config::types::McpServerConfig;
+use crate::config::types::McpServerTransportConfig;
 use crate::features::Feature;
 use crate::plugins::AppConnectorId;
 use crate::plugins::PluginCapabilitySummary;
+use crate::plugins::PluginsManager;
+use codex_protocol::mcp::Tool;
 use pretty_assertions::assert_eq;
 use std::fs;
 use std::path::Path;
+use std::sync::Arc;
 use toml::Value;
 
 fn write_file(path: &Path, contents: &str) {
@@ -79,7 +84,7 @@ fn group_tools_by_server_strips_prefix_and_groups() {
     expected.insert("alpha".to_string(), expected_alpha);
     expected.insert("beta".to_string(), expected_beta);
 
-    assert_eq!(group_tools_by_server(&tools), expected);
+    assert_eq!(types::group_tools_by_server(&tools), expected);
 }
 
 #[test]
@@ -126,19 +131,19 @@ fn tool_plugin_provenance_collects_app_and_mcp_sources() {
 #[test]
 fn codex_apps_mcp_url_for_base_url_keeps_existing_paths() {
     assert_eq!(
-        codex_apps_mcp_url_for_base_url("https://chatgpt.com/backend-api"),
+        config::codex_apps_mcp_url_for_base_url("https://chatgpt.com/backend-api"),
         "https://chatgpt.com/backend-api/wham/apps"
     );
     assert_eq!(
-        codex_apps_mcp_url_for_base_url("https://chat.openai.com"),
+        config::codex_apps_mcp_url_for_base_url("https://chat.openai.com"),
         "https://chat.openai.com/backend-api/wham/apps"
     );
     assert_eq!(
-        codex_apps_mcp_url_for_base_url("http://localhost:8080/api/codex"),
+        config::codex_apps_mcp_url_for_base_url("http://localhost:8080/api/codex"),
         "http://localhost:8080/api/codex/apps"
     );
     assert_eq!(
-        codex_apps_mcp_url_for_base_url("http://localhost:8080"),
+        config::codex_apps_mcp_url_for_base_url("http://localhost:8080"),
         "http://localhost:8080/api/codex/apps"
     );
 }
@@ -149,7 +154,7 @@ fn codex_apps_mcp_url_uses_legacy_codex_apps_path() {
     config.chatgpt_base_url = "https://chatgpt.com".to_string();
 
     assert_eq!(
-        codex_apps_mcp_url(&config),
+        config::codex_apps_mcp_url(&config),
         "https://chatgpt.com/backend-api/wham/apps"
     );
 }

codex-rs/core/src/mcp/snapshot.rs

@@ -0,0 +1,191 @@
+use std::collections::HashMap;
+use std::path::PathBuf;
+use std::sync::Arc;
+
+use async_channel::unbounded;
+use codex_protocol::mcp::Resource;
+use codex_protocol::mcp::ResourceTemplate;
+use codex_protocol::mcp::Tool;
+use codex_protocol::protocol::McpListToolsResponseEvent;
+use codex_protocol::protocol::SandboxPolicy;
+use serde_json::Value;
+
+use crate::AuthManager;
+use crate::config::Config;
+use crate::mcp::auth::compute_auth_statuses;
+use crate::mcp::types::SandboxState;
+use crate::mcp_connection_manager::McpConnectionManager;
+use crate::mcp_connection_manager::codex_apps_tools_cache_key;
+use crate::plugins::PluginsManager;
+
+use super::McpManager;
+
+pub async fn collect_mcp_snapshot(config: &Config) -> McpListToolsResponseEvent {
+    let auth_manager = AuthManager::shared(
+        config.codex_home.clone(),
+        /*enable_codex_api_key_env*/ false,
+        config.cli_auth_credentials_store_mode,
+    );
+    let auth = auth_manager.auth().await;
+    let mcp_manager = McpManager::new(Arc::new(PluginsManager::new(config.codex_home.clone())));
+    let mcp_servers = mcp_manager.effective_servers(config, auth.as_ref());
+    let tool_plugin_provenance = mcp_manager.tool_plugin_provenance(config);
+    if mcp_servers.is_empty() {
+        return McpListToolsResponseEvent {
+            tools: HashMap::new(),
+            resources: HashMap::new(),
+            resource_templates: HashMap::new(),
+            auth_statuses: HashMap::new(),
+        };
+    }
+
+    let auth_status_entries =
+        compute_auth_statuses(mcp_servers.iter(), config.mcp_oauth_credentials_store_mode).await;
+
+    let (tx_event, rx_event) = unbounded();
+    drop(rx_event);
+
+    // Use ReadOnly sandbox policy for MCP snapshot collection (safest default)
+    let sandbox_state = SandboxState {
+        sandbox_policy: SandboxPolicy::new_read_only_policy(),
+        codex_linux_sandbox_exe: config.codex_linux_sandbox_exe.clone(),
+        sandbox_cwd: std::env::current_dir().unwrap_or_else(|_| PathBuf::from("/")),
+        use_legacy_landlock: config.features.use_legacy_landlock(),
+    };
+
+    let (mcp_connection_manager, cancel_token) = McpConnectionManager::new(
+        String::new(),
+        &mcp_servers,
+        config.mcp_oauth_credentials_store_mode,
+        auth_status_entries.clone(),
+        &config.permissions.approval_policy,
+        tx_event,
+        sandbox_state,
+        config.codex_home.clone(),
+        codex_apps_tools_cache_key(auth.as_ref()),
+        tool_plugin_provenance,
+    )
+    .await;
+
+    let snapshot =
+        collect_mcp_snapshot_from_manager(&mcp_connection_manager, auth_status_entries).await;
+
+    cancel_token.cancel();
+
+    snapshot
+}
+
+pub(crate) async fn collect_mcp_snapshot_from_manager(
+    mcp_connection_manager: &McpConnectionManager,
+    auth_status_entries: HashMap<String, crate::mcp::auth::McpAuthStatusEntry>,
+) -> McpListToolsResponseEvent {
+    let (tools, resources, resource_templates) = tokio::join!(
+        mcp_connection_manager.list_all_tools(),
+        mcp_connection_manager.list_all_resources(),
+        mcp_connection_manager.list_all_resource_templates(),
+    );
+
+    let auth_statuses = auth_status_entries
+        .iter()
+        .map(|(name, entry)| (name.clone(), entry.auth_status))
+        .collect();
+
+    let tools = tools
+        .into_iter()
+        .filter_map(|(name, tool)| match serde_json::to_value(tool.tool) {
+            Ok(value) => match Tool::from_mcp_value(value) {
+                Ok(tool) => Some((name, tool)),
+                Err(err) => {
+                    tracing::warn!("Failed to convert MCP tool '{name}': {err}");
+                    None
+                }
+            },
+            Err(err) => {
+                tracing::warn!("Failed to serialize MCP tool '{name}': {err}");
+                None
+            }
+        })
+        .collect();
+
+    let resources = resources
+        .into_iter()
+        .map(|(name, resources)| {
+            let resources = resources
+                .into_iter()
+                .filter_map(|resource| match serde_json::to_value(resource) {
+                    Ok(value) => match Resource::from_mcp_value(value.clone()) {
+                        Ok(resource) => Some(resource),
+                        Err(err) => {
+                            let (uri, resource_name) = match value {
+                                Value::Object(obj) => (
+                                    obj
+                                        .get("uri")
+                                        .and_then(|v| v.as_str().map(ToString::to_string)),
+                                    obj
+                                        .get("name")
+                                        .and_then(|v| v.as_str().map(ToString::to_string)),
+                                ),
+                                _ => (None, None),
+                            };
+
+                            tracing::warn!(
+                                "Failed to convert MCP resource (uri={uri:?}, name={resource_name:?}): {err}"
+                            );
+                            None
+                        }
+                    },
+                    Err(err) => {
+                        tracing::warn!("Failed to serialize MCP resource: {err}");
+                        None
+                    }
+                })
+                .collect::<Vec<_>>();
+            (name, resources)
+        })
+        .collect();
+
+    let resource_templates = resource_templates
+        .into_iter()
+        .map(|(name, templates)| {
+            let templates = templates
+                .into_iter()
+                .filter_map(|template| match serde_json::to_value(template) {
+                    Ok(value) => match ResourceTemplate::from_mcp_value(value.clone()) {
+                        Ok(template) => Some(template),
+                        Err(err) => {
+                            let (uri_template, template_name) = match value {
+                                Value::Object(obj) => (
+                                    obj
+                                        .get("uriTemplate")
+                                        .or_else(|| obj.get("uri_template"))
+                                        .and_then(|v| v.as_str().map(ToString::to_string)),
+                                    obj
+                                        .get("name")
+                                        .and_then(|v| v.as_str().map(ToString::to_string)),
+                                ),
+                                _ => (None, None),
+                            };
+
+                            tracing::warn!(
+                            "Failed to convert MCP resource template (uri_template={uri_template:?}, name={template_name:?}): {err}"
+                            );
+                            None
+                        }
+                    },
+                    Err(err) => {
+                        tracing::warn!("Failed to serialize MCP resource template: {err}");
+                        None
+                    }
+                })
+                .collect::<Vec<_>>();
+            (name, templates)
+        })
+        .collect();
+
+    McpListToolsResponseEvent {
+        tools,
+        resources,
+        resource_templates,
+        auth_statuses,
+    }
+}

codex-rs/core/src/mcp/types.rs

@@ -0,0 +1,3 @@
+pub use codex_mcp_types::SandboxState;
+pub use codex_mcp_types::group_tools_by_server;
+pub use codex_mcp_types::split_qualified_tool_name;

codex-rs/core/src/mcp_connection_manager.rs

@@ -40,7 +40,6 @@ use codex_protocol::protocol::McpStartupCompleteEvent;
 use codex_protocol::protocol::McpStartupFailure;
 use codex_protocol::protocol::McpStartupStatus;
 use codex_protocol::protocol::McpStartupUpdateEvent;
-use codex_protocol::protocol::SandboxPolicy;
 use codex_rmcp_client::ElicitationResponse;
 use codex_rmcp_client::OAuthCredentialsStoreMode;
 use codex_rmcp_client::RmcpClient;
@@ -78,11 +77,11 @@ use tracing::instrument;
 use tracing::warn;
 use url::Url;
 
-use crate::codex::INITIAL_SUBMIT_ID;
 use crate::config::types::McpServerConfig;
 use crate::config::types::McpServerTransportConfig;
 use crate::connectors::is_connector_id_allowed;
 use crate::connectors::sanitize_name;
+use crate::mcp::types::SandboxState;
 
 /// Delimiter used to separate the server name from the tool name in a fully
 /// qualified tool name.
@@ -581,19 +580,9 @@ impl AsyncManagedClient {
 pub const MCP_SANDBOX_STATE_CAPABILITY: &str = "codex/sandbox-state";
 
 /// Custom MCP request to push sandbox state updates.
-/// When used, the `params` field of the notification is [`SandboxState`].
+/// When used, the `params` field of the notification is [`crate::SandboxState`].
 pub const MCP_SANDBOX_STATE_METHOD: &str = "codex/sandbox-state/update";
 
-#[derive(Debug, Clone, Serialize, Deserialize)]
-#[serde(rename_all = "camelCase")]
-pub struct SandboxState {
-    pub sandbox_policy: SandboxPolicy,
-    pub codex_linux_sandbox_exe: Option<PathBuf>,
-    pub sandbox_cwd: PathBuf,
-    #[serde(default)]
-    pub use_legacy_landlock: bool,
-}
-
 /// A thin wrapper around a set of running [`RmcpClient`] instances.
 pub(crate) struct McpConnectionManager {
     clients: HashMap<String, AsyncManagedClient>,
@@ -633,6 +622,7 @@ impl McpConnectionManager {
 
     #[allow(clippy::new_ret_no_self, clippy::too_many_arguments)]
     pub async fn new(
+        submit_id: String,
         mcp_servers: &HashMap<String, McpServerConfig>,
         store_mode: OAuthCredentialsStoreMode,
         auth_entries: HashMap<String, McpAuthStatusEntry>,
@@ -657,6 +647,7 @@ impl McpConnectionManager {
             let cancel_token = cancel_token.child_token();
             let _ = emit_update(
                 &tx_event,
+                submit_id.as_str(),
                 McpStartupUpdateEvent {
                     server: server_name.clone(),
                     status: McpStartupStatus::Starting,
@@ -683,6 +674,7 @@ impl McpConnectionManager {
             );
             clients.insert(server_name.clone(), async_managed_client.clone());
             let tx_event = tx_event.clone();
+            let submit_id = submit_id.clone();
             let auth_entry = auth_entries.get(&server_name).cloned();
             let sandbox_state = initial_sandbox_state.clone();
             join_set.spawn(async move {
@@ -715,6 +707,7 @@ impl McpConnectionManager {
 
                 let _ = emit_update(
                     &tx_event,
+                    submit_id.as_str(),
                     McpStartupUpdateEvent {
                         server: server_name.clone(),
                         status,
@@ -730,6 +723,7 @@ impl McpConnectionManager {
             server_origins,
             elicitation_requests: elicitation_requests.clone(),
         };
+        let submit_id_for_task = submit_id.clone();
         tokio::spawn(async move {
             let outcomes = join_set.join_all().await;
             let mut summary = McpStartupCompleteEvent::default();
@@ -747,7 +741,7 @@ impl McpConnectionManager {
             }
             let _ = tx_event
                 .send(Event {
-                    id: INITIAL_SUBMIT_ID.to_owned(),
+                    id: submit_id_for_task,
                     msg: EventMsg::McpStartupComplete(summary),
                 })
                 .await;
@@ -1133,11 +1127,12 @@ impl McpConnectionManager {
 
 async fn emit_update(
     tx_event: &Sender<Event>,
+    submit_id: &str,
     update: McpStartupUpdateEvent,
 ) -> Result<(), async_channel::SendError<Event>> {
     tx_event
         .send(Event {
-            id: INITIAL_SUBMIT_ID.to_owned(),
+            id: submit_id.to_owned(),
             msg: EventMsg::McpStartupUpdate(update),
         })
         .await

codex-rs/core/src/tools/handlers/view_image.rs

@@ -1,5 +1,4 @@
 use async_trait::async_trait;
-use codex_environment::ExecutorFileSystem;
 use codex_protocol::models::ContentItem;
 use codex_protocol::models::FunctionCallOutputContentItem;
 use codex_protocol::models::ImageDetail;

codex-rs/core/src/tools/runtimes/unified_exec.rs

@@ -46,6 +46,7 @@ use std::path::PathBuf;
 
 #[derive(Clone, Debug)]
 pub struct UnifiedExecRequest {
+    pub process_id: i32,
     pub command: Vec<String>,
     pub cwd: PathBuf,
     pub env: HashMap<String, String>,
@@ -239,6 +240,7 @@ impl<'a> ToolRuntime<UnifiedExecRequest, UnifiedExecProcess> for UnifiedExecRunt
                     return self
                         .manager
                         .open_session_with_exec_env(
+                            req.process_id,
                             &prepared.exec_request,
                             req.tty,
                             prepared.spawn_lifecycle,
@@ -275,7 +277,12 @@ impl<'a> ToolRuntime<UnifiedExecRequest, UnifiedExecProcess> for UnifiedExecRunt
             .env_for(spec, req.network.as_ref())
             .map_err(|err| ToolError::Codex(err.into()))?;
         self.manager
-            .open_session_with_exec_env(&exec_env, req.tty, Box::new(NoopSpawnLifecycle))
+            .open_session_with_exec_env(
+                req.process_id,
+                &exec_env,
+                req.tty,
+                Box::new(NoopSpawnLifecycle),
+            )
             .await
             .map_err(|err| match err {
                 UnifiedExecError::SandboxDenied { output, .. } => {

codex-rs/core/src/tools/spec.rs

@@ -49,6 +49,10 @@ use codex_protocol::openai_models::WebSearchToolType;
 use codex_protocol::protocol::SandboxPolicy;
 use codex_protocol::protocol::SessionSource;
 use codex_protocol::protocol::SubAgentSource;
+#[cfg(test)]
+pub use codex_tool_spec::AdditionalProperties;
+pub use codex_tool_spec::JsonSchema;
+pub use codex_tool_spec::parse_tool_input_schema;
 use codex_utils_absolute_path::AbsolutePathBuf;
 use serde::Deserialize;
 use serde::Serialize;
@@ -467,62 +471,6 @@ fn supports_image_generation(model_info: &ModelInfo) -> bool {
     model_info.input_modalities.contains(&InputModality::Image)
 }
 
-/// Generic JSON‑Schema subset needed for our tool definitions
-#[derive(Debug, Clone, Serialize, Deserialize, PartialEq)]
-#[serde(tag = "type", rename_all = "lowercase")]
-pub enum JsonSchema {
-    Boolean {
-        #[serde(skip_serializing_if = "Option::is_none")]
-        description: Option<String>,
-    },
-    String {
-        #[serde(skip_serializing_if = "Option::is_none")]
-        description: Option<String>,
-    },
-    /// MCP schema allows "number" | "integer" for Number
-    #[serde(alias = "integer")]
-    Number {
-        #[serde(skip_serializing_if = "Option::is_none")]
-        description: Option<String>,
-    },
-    Array {
-        items: Box<JsonSchema>,
-
-        #[serde(skip_serializing_if = "Option::is_none")]
-        description: Option<String>,
-    },
-    Object {
-        properties: BTreeMap<String, JsonSchema>,
-        #[serde(skip_serializing_if = "Option::is_none")]
-        required: Option<Vec<String>>,
-        #[serde(
-            rename = "additionalProperties",
-            skip_serializing_if = "Option::is_none"
-        )]
-        additional_properties: Option<AdditionalProperties>,
-    },
-}
-
-/// Whether additional properties are allowed, and if so, any required schema
-#[derive(Debug, Clone, Serialize, Deserialize, PartialEq)]
-#[serde(untagged)]
-pub enum AdditionalProperties {
-    Boolean(bool),
-    Schema(Box<JsonSchema>),
-}
-
-impl From<bool> for AdditionalProperties {
-    fn from(b: bool) -> Self {
-        Self::Boolean(b)
-    }
-}
-
-impl From<JsonSchema> for AdditionalProperties {
-    fn from(s: JsonSchema) -> Self {
-        Self::Schema(Box::new(s))
-    }
-}
-
 fn create_network_permissions_schema() -> JsonSchema {
     JsonSchema::Object {
         properties: BTreeMap::from([(
@@ -2240,19 +2188,16 @@ pub(crate) struct ApplyPatchToolArgs {
 /// Returns JSON values that are compatible with Function Calling in the
 /// Responses API:
 /// https://platform.openai.com/docs/guides/function-calling?api-mode=responses
+///
+/// API stability: this helper remains available from `crate::tools::spec`, but
+/// its implementation moved under `client_common` so the model client can
+/// serialize tool payloads without depending on the full tool registry builder.
+#[allow(dead_code)] // Kept for internal tests and legacy in-crate call sites.
 pub fn create_tools_json_for_responses_api(
     tools: &[ToolSpec],
 ) -> crate::error::Result<Vec<serde_json::Value>> {
-    let mut tools_json = Vec::new();
-
-    for tool in tools {
-        let json = serde_json::to_value(tool)?;
-        tools_json.push(json);
-    }
-
-    Ok(tools_json)
+    crate::client_common::create_tools_json_for_responses_api(tools)
 }
-
 fn push_tool_spec(
     builder: &mut ToolRegistryBuilder,
     spec: ToolSpec,
@@ -2314,13 +2259,6 @@ fn dynamic_tool_to_openai_tool(
     })
 }
 
-/// Parse the tool input_schema or return an error for invalid schema
-pub fn parse_tool_input_schema(input_schema: &JsonValue) -> Result<JsonSchema, serde_json::Error> {
-    let mut input_schema = input_schema.clone();
-    sanitize_json_schema(&mut input_schema);
-    serde_json::from_value::<JsonSchema>(input_schema)
-}
-
 fn mcp_tool_to_openai_tool_parts(
     tool: rmcp::model::Tool,
 ) -> Result<(String, JsonSchema, Option<JsonValue>), serde_json::Error> {
@@ -2345,13 +2283,7 @@ fn mcp_tool_to_openai_tool_parts(
         );
     }
 
-    // Serialize to a raw JSON value so we can sanitize schemas coming from MCP
-    // servers. Some servers omit the top-level or nested `type` in JSON
-    // Schemas (e.g. using enum/anyOf), or use unsupported variants like
-    // `integer`. Our internal JsonSchema is a small subset and requires
-    // `type`, so we coerce/sanitize here for compatibility.
-    sanitize_json_schema(&mut serialized_input_schema);
-    let input_schema = serde_json::from_value::<JsonSchema>(serialized_input_schema)?;
+    let input_schema = parse_tool_input_schema(&serialized_input_schema)?;
     let structured_content_schema = output_schema
         .map(|output_schema| serde_json::Value::Object(output_schema.as_ref().clone()))
         .unwrap_or_else(|| JsonValue::Object(serde_json::Map::new()));
@@ -2382,117 +2314,6 @@ fn mcp_call_tool_result_output_schema(structured_content_schema: JsonValue) -> J
     })
 }
 
-/// Sanitize a JSON Schema (as serde_json::Value) so it can fit our limited
-/// JsonSchema enum. This function:
-/// - Ensures every schema object has a "type". If missing, infers it from
-///   common keywords (properties => object, items => array, enum/const/format => string)
-///   and otherwise defaults to "string".
-/// - Fills required child fields (e.g. array items, object properties) with
-///   permissive defaults when absent.
-fn sanitize_json_schema(value: &mut JsonValue) {
-    match value {
-        JsonValue::Bool(_) => {
-            // JSON Schema boolean form: true/false. Coerce to an accept-all string.
-            *value = json!({ "type": "string" });
-        }
-        JsonValue::Array(arr) => {
-            for v in arr.iter_mut() {
-                sanitize_json_schema(v);
-            }
-        }
-        JsonValue::Object(map) => {
-            // First, recursively sanitize known nested schema holders
-            if let Some(props) = map.get_mut("properties")
-                && let Some(props_map) = props.as_object_mut()
-            {
-                for (_k, v) in props_map.iter_mut() {
-                    sanitize_json_schema(v);
-                }
-            }
-            if let Some(items) = map.get_mut("items") {
-                sanitize_json_schema(items);
-            }
-            // Some schemas use oneOf/anyOf/allOf - sanitize their entries
-            for combiner in ["oneOf", "anyOf", "allOf", "prefixItems"] {
-                if let Some(v) = map.get_mut(combiner) {
-                    sanitize_json_schema(v);
-                }
-            }
-
-            // Normalize/ensure type
-            let mut ty = map.get("type").and_then(|v| v.as_str()).map(str::to_string);
-
-            // If type is an array (union), pick first supported; else leave to inference
-            if ty.is_none()
-                && let Some(JsonValue::Array(types)) = map.get("type")
-            {
-                for t in types {
-                    if let Some(tt) = t.as_str()
-                        && matches!(
-                            tt,
-                            "object" | "array" | "string" | "number" | "integer" | "boolean"
-                        )
-                    {
-                        ty = Some(tt.to_string());
-                        break;
-                    }
-                }
-            }
-
-            // Infer type if still missing
-            if ty.is_none() {
-                if map.contains_key("properties")
-                    || map.contains_key("required")
-                    || map.contains_key("additionalProperties")
-                {
-                    ty = Some("object".to_string());
-                } else if map.contains_key("items") || map.contains_key("prefixItems") {
-                    ty = Some("array".to_string());
-                } else if map.contains_key("enum")
-                    || map.contains_key("const")
-                    || map.contains_key("format")
-                {
-                    ty = Some("string".to_string());
-                } else if map.contains_key("minimum")
-                    || map.contains_key("maximum")
-                    || map.contains_key("exclusiveMinimum")
-                    || map.contains_key("exclusiveMaximum")
-                    || map.contains_key("multipleOf")
-                {
-                    ty = Some("number".to_string());
-                }
-            }
-            // If we still couldn't infer, default to string
-            let ty = ty.unwrap_or_else(|| "string".to_string());
-            map.insert("type".to_string(), JsonValue::String(ty.to_string()));
-
-            // Ensure object schemas have properties map
-            if ty == "object" {
-                if !map.contains_key("properties") {
-                    map.insert(
-                        "properties".to_string(),
-                        JsonValue::Object(serde_json::Map::new()),
-                    );
-                }
-                // If additionalProperties is an object schema, sanitize it too.
-                // Leave booleans as-is, since JSON Schema allows boolean here.
-                if let Some(ap) = map.get_mut("additionalProperties") {
-                    let is_bool = matches!(ap, JsonValue::Bool(_));
-                    if !is_bool {
-                        sanitize_json_schema(ap);
-                    }
-                }
-            }
-
-            // Ensure array schemas have items
-            if ty == "array" && !map.contains_key("items") {
-                map.insert("items".to_string(), json!({ "type": "string" }));
-            }
-        }
-        _ => {}
-    }
-}
-
 /// Builds the tool registry builder while collecting tool specs for later serialization.
 #[cfg(test)]
 pub(crate) fn build_specs(

codex-rs/core/src/tools/spec_tests.rs

@@ -2777,7 +2777,7 @@ fn chat_tools_include_top_level_name() {
         output_schema: None,
     })];
 
-    let responses_json = create_tools_json_for_responses_api(&tools).unwrap();
+    let responses_json = crate::client_tools::create_tools_json_for_responses_api(&tools).unwrap();
     assert_eq!(
         responses_json,
         vec![json!({

codex-rs/core/src/unified_exec/backend.rs

@@ -0,0 +1,116 @@
+use std::path::PathBuf;
+
+use codex_exec_server::ExecServerClient;
+use codex_exec_server::RemoteExecServerConnectArgs;
+
+use crate::config::Config;
+use crate::exec::SandboxType;
+use crate::sandboxing::ExecRequest;
+use crate::unified_exec::RemoteExecServerFileSystem;
+use crate::unified_exec::SpawnLifecycleHandle;
+use crate::unified_exec::UnifiedExecError;
+use crate::unified_exec::UnifiedExecProcess;
+
+#[derive(Clone)]
+pub(crate) struct RemoteExecServerBackend {
+    client: ExecServerClient,
+    local_workspace_root: PathBuf,
+    remote_workspace_root: Option<PathBuf>,
+}
+
+impl std::fmt::Debug for RemoteExecServerBackend {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("RemoteExecServerBackend")
+            .field("local_workspace_root", &self.local_workspace_root)
+            .field("remote_workspace_root", &self.remote_workspace_root)
+            .finish_non_exhaustive()
+    }
+}
+
+impl RemoteExecServerBackend {
+    pub(crate) async fn connect_for_config(
+        config: &Config,
+    ) -> Result<Option<Self>, UnifiedExecError> {
+        let Some(websocket_url) = config
+            .experimental_unified_exec_exec_server_websocket_url
+            .clone()
+        else {
+            return Ok(None);
+        };
+
+        let client = ExecServerClient::connect_websocket(RemoteExecServerConnectArgs::new(
+            websocket_url,
+            "codex-core".to_string(),
+        ))
+        .await
+        .map_err(|err| UnifiedExecError::create_process(err.to_string()))?;
+
+        Ok(Some(Self {
+            client,
+            local_workspace_root: config.cwd.clone(),
+            remote_workspace_root: config
+                .experimental_unified_exec_exec_server_workspace_root
+                .clone()
+                .map(PathBuf::from),
+        }))
+    }
+
+    pub(crate) async fn open_session(
+        &self,
+        process_id: i32,
+        env: &ExecRequest,
+        tty: bool,
+        spawn_lifecycle: SpawnLifecycleHandle,
+    ) -> Result<UnifiedExecProcess, UnifiedExecError> {
+        if !spawn_lifecycle.inherited_fds().is_empty() {
+            return Err(UnifiedExecError::create_process(
+                "remote exec-server mode does not support inherited file descriptors".to_string(),
+            ));
+        }
+
+        if env.sandbox != SandboxType::None {
+            return Err(UnifiedExecError::create_process(format!(
+                "remote exec-server mode does not support sandboxed execution yet: {:?}",
+                env.sandbox
+            )));
+        }
+
+        let remote_cwd = self.map_remote_cwd(env.cwd.as_path())?;
+        UnifiedExecProcess::from_exec_server(
+            self.client.clone(),
+            process_id,
+            env,
+            remote_cwd,
+            tty,
+            spawn_lifecycle,
+        )
+        .await
+    }
+
+    pub(crate) fn file_system(&self) -> RemoteExecServerFileSystem {
+        RemoteExecServerFileSystem::new(self.client.clone())
+    }
+
+    fn map_remote_cwd(&self, local_cwd: &std::path::Path) -> Result<PathBuf, UnifiedExecError> {
+        let Some(remote_root) = self.remote_workspace_root.as_ref() else {
+            if local_cwd == self.local_workspace_root.as_path() {
+                return Ok(PathBuf::from("."));
+            }
+            return Err(UnifiedExecError::create_process(format!(
+                "remote exec-server mode needs `experimental_unified_exec_exec_server_workspace_root` for non-root cwd `{}`",
+                local_cwd.display()
+            )));
+        };
+
+        let relative =
+            UnifiedExecProcess::relative_cwd_under(local_cwd, &self.local_workspace_root)
+                .ok_or_else(|| {
+                    UnifiedExecError::create_process(format!(
+                        "cwd `{}` is not under local workspace root `{}`",
+                        local_cwd.display(),
+                        self.local_workspace_root.display()
+                    ))
+                })?;
+        Ok(remote_root.join(relative))
+    }
+}

codex-rs/core/src/unified_exec/mod.rs

@@ -38,21 +38,25 @@ use crate::codex::TurnContext;
 use crate::sandboxing::SandboxPermissions;
 
 mod async_watcher;
+mod backend;
 mod errors;
 mod head_tail_buffer;
 mod process;
 mod process_manager;
+mod remote_filesystem;
 
 pub(crate) fn set_deterministic_process_ids_for_tests(enabled: bool) {
     process_manager::set_deterministic_process_ids_for_tests(enabled);
 }
 
+pub(crate) use backend::RemoteExecServerBackend;
 pub(crate) use errors::UnifiedExecError;
 pub(crate) use process::NoopSpawnLifecycle;
 #[cfg(unix)]
 pub(crate) use process::SpawnLifecycle;
 pub(crate) use process::SpawnLifecycleHandle;
 pub(crate) use process::UnifiedExecProcess;
+pub(crate) use remote_filesystem::RemoteExecServerFileSystem;
 
 pub(crate) const MIN_YIELD_TIME_MS: u64 = 250;
 // Minimum yield time for an empty `write_stdin`.
@@ -123,6 +127,7 @@ impl ProcessStore {
 pub(crate) struct UnifiedExecProcessManager {
     process_store: Mutex<ProcessStore>,
     max_write_stdin_yield_time_ms: u64,
+    remote_exec_server: Option<RemoteExecServerBackend>,
 }
 
 impl UnifiedExecProcessManager {
@@ -131,6 +136,19 @@ impl UnifiedExecProcessManager {
             process_store: Mutex::new(ProcessStore::default()),
             max_write_stdin_yield_time_ms: max_write_stdin_yield_time_ms
                 .max(MIN_EMPTY_YIELD_TIME_MS),
+            remote_exec_server: None,
+        }
+    }
+
+    pub(crate) fn with_remote_exec_server(
+        max_write_stdin_yield_time_ms: u64,
+        remote_exec_server: Option<RemoteExecServerBackend>,
+    ) -> Self {
+        Self {
+            process_store: Mutex::new(ProcessStore::default()),
+            max_write_stdin_yield_time_ms: max_write_stdin_yield_time_ms
+                .max(MIN_EMPTY_YIELD_TIME_MS),
+            remote_exec_server,
         }
     }
 }

codex-rs/core/src/unified_exec/process.rs

@@ -1,6 +1,7 @@
 #![allow(clippy::module_inception)]
 
 use std::sync::Arc;
+use std::sync::Mutex as StdMutex;
 use std::sync::atomic::AtomicBool;
 use std::sync::atomic::Ordering;
 use tokio::sync::Mutex;
@@ -16,8 +17,13 @@ use crate::exec::ExecToolCallOutput;
 use crate::exec::SandboxType;
 use crate::exec::StreamOutput;
 use crate::exec::is_likely_sandbox_denied;
+use crate::sandboxing::ExecRequest;
 use crate::truncate::TruncationPolicy;
 use crate::truncate::formatted_truncate_text;
+use codex_exec_server::ExecParams;
+use codex_exec_server::ExecServerClient;
+use codex_exec_server::ExecServerEvent;
+use codex_utils_absolute_path::AbsolutePathBuf;
 use codex_utils_pty::ExecCommandSession;
 use codex_utils_pty::SpawnedPty;
 
@@ -56,7 +62,7 @@ pub(crate) struct OutputHandles {
 
 #[derive(Debug)]
 pub(crate) struct UnifiedExecProcess {
-    process_handle: ExecCommandSession,
+    process_handle: ProcessBackend,
     output_rx: broadcast::Receiver<Vec<u8>>,
     output_buffer: OutputBuffer,
     output_notify: Arc<Notify>,
@@ -69,9 +75,45 @@ pub(crate) struct UnifiedExecProcess {
     _spawn_lifecycle: SpawnLifecycleHandle,
 }
 
+enum ProcessBackend {
+    Local(ExecCommandSession),
+    Remote(RemoteExecSession),
+}
+
+impl std::fmt::Debug for ProcessBackend {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Self::Local(process_handle) => f.debug_tuple("Local").field(process_handle).finish(),
+            Self::Remote(process_handle) => f.debug_tuple("Remote").field(process_handle).finish(),
+        }
+    }
+}
+
+#[derive(Clone)]
+struct RemoteExecSession {
+    process_key: String,
+    client: ExecServerClient,
+    writer_tx: mpsc::Sender<Vec<u8>>,
+    exited: Arc<AtomicBool>,
+    exit_code: Arc<StdMutex<Option<i32>>>,
+}
+
+impl std::fmt::Debug for RemoteExecSession {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("RemoteExecSession")
+            .field("process_key", &self.process_key)
+            .field("exited", &self.exited.load(Ordering::SeqCst))
+            .field(
+                "exit_code",
+                &self.exit_code.lock().ok().and_then(|guard| *guard),
+            )
+            .finish_non_exhaustive()
+    }
+}
+
 impl UnifiedExecProcess {
-    pub(super) fn new(
-        process_handle: ExecCommandSession,
+    fn new(
+        process_handle: ProcessBackend,
         initial_output_rx: tokio::sync::broadcast::Receiver<Vec<u8>>,
         sandbox_type: SandboxType,
         spawn_lifecycle: SpawnLifecycleHandle,
@@ -123,7 +165,10 @@ impl UnifiedExecProcess {
     }
 
     pub(super) fn writer_sender(&self) -> mpsc::Sender<Vec<u8>> {
-        self.process_handle.writer_sender()
+        match &self.process_handle {
+            ProcessBackend::Local(process_handle) => process_handle.writer_sender(),
+            ProcessBackend::Remote(process_handle) => process_handle.writer_tx.clone(),
+        }
     }
 
     pub(super) fn output_handles(&self) -> OutputHandles {
@@ -149,17 +194,38 @@ impl UnifiedExecProcess {
     }
 
     pub(super) fn has_exited(&self) -> bool {
-        self.process_handle.has_exited()
+        match &self.process_handle {
+            ProcessBackend::Local(process_handle) => process_handle.has_exited(),
+            ProcessBackend::Remote(process_handle) => process_handle.exited.load(Ordering::SeqCst),
+        }
     }
 
     pub(super) fn exit_code(&self) -> Option<i32> {
-        self.process_handle.exit_code()
+        match &self.process_handle {
+            ProcessBackend::Local(process_handle) => process_handle.exit_code(),
+            ProcessBackend::Remote(process_handle) => process_handle
+                .exit_code
+                .lock()
+                .ok()
+                .and_then(|guard| *guard),
+        }
     }
 
     pub(super) fn terminate(&self) {
         self.output_closed.store(true, Ordering::Release);
         self.output_closed_notify.notify_waiters();
-        self.process_handle.terminate();
+        match &self.process_handle {
+            ProcessBackend::Local(process_handle) => process_handle.terminate(),
+            ProcessBackend::Remote(process_handle) => {
+                let client = process_handle.client.clone();
+                let process_key = process_handle.process_key.clone();
+                if let Ok(handle) = tokio::runtime::Handle::try_current() {
+                    handle.spawn(async move {
+                        let _ = client.terminate(&process_key).await;
+                    });
+                }
+            }
+        }
         self.cancellation_token.cancel();
         self.output_task.abort();
     }
@@ -232,7 +298,12 @@ impl UnifiedExecProcess {
             mut exit_rx,
         } = spawned;
         let output_rx = codex_utils_pty::combine_output_receivers(stdout_rx, stderr_rx);
-        let managed = Self::new(process_handle, output_rx, sandbox_type, spawn_lifecycle);
+        let managed = Self::new(
+            ProcessBackend::Local(process_handle),
+            output_rx,
+            sandbox_type,
+            spawn_lifecycle,
+        );
 
         let exit_ready = matches!(exit_rx.try_recv(), Ok(_) | Err(TryRecvError::Closed));
 
@@ -262,6 +333,102 @@ impl UnifiedExecProcess {
         Ok(managed)
     }
 
+    pub(super) async fn from_exec_server(
+        client: ExecServerClient,
+        process_id: i32,
+        env: &ExecRequest,
+        remote_cwd: std::path::PathBuf,
+        tty: bool,
+        spawn_lifecycle: SpawnLifecycleHandle,
+    ) -> Result<Self, UnifiedExecError> {
+        let process_key = process_id.to_string();
+        let mut events_rx = client.event_receiver();
+        let response = client
+            .exec(ExecParams {
+                process_id: process_key.clone(),
+                argv: env.command.clone(),
+                cwd: remote_cwd,
+                env: env.env.clone(),
+                tty,
+                arg0: env.arg0.clone(),
+                sandbox: None,
+            })
+            .await
+            .map_err(|err| UnifiedExecError::create_process(err.to_string()))?;
+        let process_key = response.process_id;
+
+        let (output_tx, output_rx) = broadcast::channel(256);
+        let (writer_tx, mut writer_rx) = mpsc::channel::<Vec<u8>>(256);
+        let exited = Arc::new(AtomicBool::new(false));
+        let exit_code = Arc::new(StdMutex::new(None));
+
+        let managed = Self::new(
+            ProcessBackend::Remote(RemoteExecSession {
+                process_key: process_key.clone(),
+                client: client.clone(),
+                writer_tx,
+                exited: Arc::clone(&exited),
+                exit_code: Arc::clone(&exit_code),
+            }),
+            output_rx,
+            env.sandbox,
+            spawn_lifecycle,
+        );
+
+        {
+            let client = client.clone();
+            let writer_process_key = process_key.clone();
+            tokio::spawn(async move {
+                while let Some(chunk) = writer_rx.recv().await {
+                    if client.write(&writer_process_key, chunk).await.is_err() {
+                        break;
+                    }
+                }
+            });
+        }
+
+        {
+            let cancellation_token = managed.cancellation_token();
+            tokio::spawn(async move {
+                while let Ok(event) = events_rx.recv().await {
+                    match event {
+                        ExecServerEvent::OutputDelta(notification)
+                            if notification.process_id == process_key =>
+                        {
+                            let _ = output_tx.send(notification.chunk.into_inner());
+                        }
+                        ExecServerEvent::Exited(notification)
+                            if notification.process_id == process_key =>
+                        {
+                            exited.store(true, Ordering::SeqCst);
+                            if let Ok(mut guard) = exit_code.lock() {
+                                *guard = Some(notification.exit_code);
+                            }
+                            cancellation_token.cancel();
+                            break;
+                        }
+                        ExecServerEvent::OutputDelta(_) | ExecServerEvent::Exited(_) => {}
+                    }
+                }
+            });
+        }
+
+        Ok(managed)
+    }
+
+    pub(super) fn relative_cwd_under(
+        local_cwd: &std::path::Path,
+        local_root: &std::path::Path,
+    ) -> Option<std::path::PathBuf> {
+        let local_cwd = AbsolutePathBuf::try_from(local_cwd.to_path_buf()).ok()?;
+        let local_root = AbsolutePathBuf::try_from(local_root.to_path_buf()).ok()?;
+        local_cwd
+            .as_path()
+            .strip_prefix(local_root.as_path())
+            .ok()
+            .map(std::path::Path::to_path_buf)
+    }
+
     fn signal_exit(&self) {
         self.cancellation_token.cancel();
     }

codex-rs/core/src/unified_exec/process_manager.rs

@@ -539,10 +539,17 @@ impl UnifiedExecProcessManager {
 
     pub(crate) async fn open_session_with_exec_env(
         &self,
+        process_id: i32,
         env: &ExecRequest,
         tty: bool,
         mut spawn_lifecycle: SpawnLifecycleHandle,
     ) -> Result<UnifiedExecProcess, UnifiedExecError> {
+        if let Some(remote_exec_server) = self.remote_exec_server.as_ref() {
+            return remote_exec_server
+                .open_session(process_id, env, tty, spawn_lifecycle)
+                .await;
+        }
+
         let (program, args) = env
             .command
             .split_first()
@@ -610,6 +617,7 @@ impl UnifiedExecProcessManager {
             })
             .await;
         let req = UnifiedExecToolRequest {
+            process_id: request.process_id,
             command: request.command.clone(),
             cwd,
             env,

codex-rs/core/src/unified_exec/remote_filesystem.rs

@@ -0,0 +1,152 @@
+use std::io;
+
+use async_trait::async_trait;
+use base64::Engine as _;
+use base64::engine::general_purpose::STANDARD;
+use codex_app_server_protocol::FsCopyParams;
+use codex_app_server_protocol::FsCreateDirectoryParams;
+use codex_app_server_protocol::FsGetMetadataParams;
+use codex_app_server_protocol::FsReadDirectoryParams;
+use codex_app_server_protocol::FsReadFileParams;
+use codex_app_server_protocol::FsRemoveParams;
+use codex_app_server_protocol::FsWriteFileParams;
+use codex_environment::CopyOptions;
+use codex_environment::CreateDirectoryOptions;
+use codex_environment::ExecutorFileSystem;
+use codex_environment::FileMetadata;
+use codex_environment::FileSystemResult;
+use codex_environment::ReadDirectoryEntry;
+use codex_environment::RemoveOptions;
+use codex_exec_server::ExecServerClient;
+use codex_exec_server::ExecServerError;
+use codex_utils_absolute_path::AbsolutePathBuf;
+
+/// Filesystem backend that forwards environment operations to a remote
+/// `codex-exec-server`.
+#[derive(Clone)]
+pub(crate) struct RemoteExecServerFileSystem {
+    client: ExecServerClient,
+}
+
+impl RemoteExecServerFileSystem {
+    pub(crate) fn new(client: ExecServerClient) -> Self {
+        Self { client }
+    }
+}
+
+impl std::fmt::Debug for RemoteExecServerFileSystem {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("RemoteExecServerFileSystem")
+            .finish_non_exhaustive()
+    }
+}
+
+#[async_trait]
+impl ExecutorFileSystem for RemoteExecServerFileSystem {
+    async fn read_file(&self, path: &AbsolutePathBuf) -> FileSystemResult<Vec<u8>> {
+        let response = self
+            .client
+            .fs_read_file(FsReadFileParams { path: path.clone() })
+            .await
+            .map_err(map_exec_server_error)?;
+        STANDARD.decode(response.data_base64).map_err(|error| {
+            io::Error::new(
+                io::ErrorKind::InvalidData,
+                format!("remote exec-server returned invalid base64 file data: {error}"),
+            )
+        })
+    }
+
+    async fn write_file(&self, path: &AbsolutePathBuf, contents: Vec<u8>) -> FileSystemResult<()> {
+        self.client
+            .fs_write_file(FsWriteFileParams {
+                path: path.clone(),
+                data_base64: STANDARD.encode(contents),
+            })
+            .await
+            .map_err(map_exec_server_error)?;
+        Ok(())
+    }
+
+    async fn create_directory(
+        &self,
+        path: &AbsolutePathBuf,
+        options: CreateDirectoryOptions,
+    ) -> FileSystemResult<()> {
+        self.client
+            .fs_create_directory(FsCreateDirectoryParams {
+                path: path.clone(),
+                recursive: Some(options.recursive),
+            })
+            .await
+            .map_err(map_exec_server_error)?;
+        Ok(())
+    }
+
+    async fn get_metadata(&self, path: &AbsolutePathBuf) -> FileSystemResult<FileMetadata> {
+        let response = self
+            .client
+            .fs_get_metadata(FsGetMetadataParams { path: path.clone() })
+            .await
+            .map_err(map_exec_server_error)?;
+        Ok(FileMetadata {
+            is_directory: response.is_directory,
+            is_file: response.is_file,
+            created_at_ms: response.created_at_ms,
+            modified_at_ms: response.modified_at_ms,
+        })
+    }
+
+    async fn read_directory(
+        &self,
+        path: &AbsolutePathBuf,
+    ) -> FileSystemResult<Vec<ReadDirectoryEntry>> {
+        let response = self
+            .client
+            .fs_read_directory(FsReadDirectoryParams { path: path.clone() })
+            .await
+            .map_err(map_exec_server_error)?;
+        Ok(response
+            .entries
+            .into_iter()
+            .map(|entry| ReadDirectoryEntry {
+                file_name: entry.file_name,
+                is_directory: entry.is_directory,
+                is_file: entry.is_file,
+            })
+            .collect())
+    }
+
+    async fn remove(&self, path: &AbsolutePathBuf, options: RemoveOptions) -> FileSystemResult<()> {
+        self.client
+            .fs_remove(FsRemoveParams {
+                path: path.clone(),
+                recursive: Some(options.recursive),
+                force: Some(options.force),
+            })
+            .await
+            .map_err(map_exec_server_error)?;
+        Ok(())
+    }
+
+    async fn copy(
+        &self,
+        source_path: &AbsolutePathBuf,
+        destination_path: &AbsolutePathBuf,
+        options: CopyOptions,
+    ) -> FileSystemResult<()> {
+        self.client
+            .fs_copy(FsCopyParams {
+                source_path: source_path.clone(),
+                destination_path: destination_path.clone(),
+                recursive: options.recursive,
+            })
+            .await
+            .map_err(map_exec_server_error)?;
+        Ok(())
+    }
+}
+
+fn map_exec_server_error(error: ExecServerError) -> io::Error {
+    io::Error::other(error.to_string())
+}

codex-rs/environment/src/lib.rs

@@ -8,11 +8,37 @@ pub use fs::FileSystemResult;
 pub use fs::ReadDirectoryEntry;
 pub use fs::RemoveOptions;
 
-#[derive(Clone, Debug, Default)]
-pub struct Environment;
+use std::sync::Arc;
+
+#[derive(Clone)]
+pub struct Environment {
+    file_system: Arc<dyn ExecutorFileSystem>,
+}
 
 impl Environment {
-    pub fn get_filesystem(&self) -> impl ExecutorFileSystem + use<> {
-        fs::LocalFileSystem
+    pub fn local() -> Self {
+        Self {
+            file_system: Arc::new(fs::LocalFileSystem),
+        }
+    }
+
+    pub fn with_file_system(file_system: Arc<dyn ExecutorFileSystem>) -> Self {
+        Self { file_system }
+    }
+
+    pub fn get_filesystem(&self) -> Arc<dyn ExecutorFileSystem> {
+        Arc::clone(&self.file_system)
+    }
+}
+
+impl Default for Environment {
+    fn default() -> Self {
+        Self::local()
+    }
+}
+
+impl std::fmt::Debug for Environment {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("Environment").finish_non_exhaustive()
     }
 }

codex-rs/exec-server/Cargo.toml

@@ -0,0 +1,40 @@
+[package]
+name = "codex-exec-server"
+version.workspace = true
+edition.workspace = true
+license.workspace = true
+
+[[bin]]
+name = "codex-exec-server"
+path = "src/bin/codex-exec-server.rs"
+
+[lints]
+workspace = true
+
+[dependencies]
+base64 = { workspace = true }
+clap = { workspace = true, features = ["derive"] }
+codex-app-server-protocol = { workspace = true }
+codex-environment = { workspace = true }
+codex-utils-pty = { workspace = true }
+futures = { workspace = true }
+serde = { workspace = true, features = ["derive"] }
+serde_json = { workspace = true }
+thiserror = { workspace = true }
+tokio = { workspace = true, features = [
+    "io-std",
+    "io-util",
+    "macros",
+    "net",
+    "process",
+    "rt-multi-thread",
+    "sync",
+    "time",
+] }
+tokio-tungstenite = { workspace = true }
+tracing = { workspace = true }
+
+[dev-dependencies]
+anyhow = { workspace = true }
+codex-utils-cargo-bin = { workspace = true }
+pretty_assertions = { workspace = true }

codex-rs/exec-server/DESIGN.md

@@ -0,0 +1,242 @@
+# exec-server design notes
+
+This document sketches a likely direction for integrating `codex-exec-server`
+with unified exec without baking the full tool-call policy stack into the
+server.
+
+The goal is:
+
+- keep exec-server generic and reusable
+- keep approval, sandbox, and retry policy in `core`
+- preserve the unified-exec event flow the model already depends on
+- support retained output caps so polling and snapshot-style APIs do not grow
+  memory without bound
+
+## Unified exec today
+
+Today the flow for LLM-visible interactive execution is:
+
+1. The model sees the `exec_command` and `write_stdin` tools.
+2. `UnifiedExecHandler` parses the tool arguments and allocates a process id.
+3. `UnifiedExecProcessManager::exec_command(...)` calls
+   `open_session_with_sandbox(...)`.
+4. `ToolOrchestrator` drives approval, sandbox selection, managed network
+   approval, and sandbox-denial retry behavior.
+5. `UnifiedExecRuntime` builds a `CommandSpec`, asks the current
+   `SandboxAttempt` to transform it into an `ExecRequest`, and passes that
+   resolved request back to the process manager.
+6. `open_session_with_exec_env(...)` spawns the process from that resolved
+   `ExecRequest`.
+7. Unified exec emits an `ExecCommandBegin` event.
+8. Unified exec starts a background output watcher that emits
+   `ExecCommandOutputDelta` events.
+9. The initial tool call collects output until the requested yield deadline and
+   returns an `ExecCommandToolOutput` snapshot to the model.
+10. If the process is still running, unified exec stores it and later emits
+    `ExecCommandEnd` when the exit watcher fires.
+11. A later `write_stdin` tool call writes to the stored process, emits a
+    `TerminalInteraction` event, collects another bounded snapshot, and returns
+    that tool response to the model.
+
+Important observation: the 250ms / 10s yield-window behavior is not really a
+process-server concern. It is a client-side convenience layer for the LLM tool
+API. The server should focus on raw process lifecycle and streaming events.
+
+## Proposed boundary
+
+The clean split is:
+
+- exec-server server: process lifecycle, output streaming, retained output caps
+- exec-server client: `wait`, `communicate`, yield-window helpers, session
+  bookkeeping
+- unified exec in `core`: tool parsing, event emission, approvals, sandboxing,
+  managed networking, retry semantics
+
+If exec-server is used by unified exec later, the boundary should sit between
+step 5 and step 6 above: after policy has produced a resolved spawn request, but
+before the actual PTY or pipe spawn.
+
+## Suggested process API
+
+Start simple and explicit:
+
+- `process/start`
+- `process/write`
+- `process/closeStdin`
+- `process/resize`
+- `process/terminate`
+- `process/wait`
+- `process/snapshot`
+
+Server notifications:
+
+- `process/output`
+- `process/exited`
+- optionally `process/started`
+- optionally `process/failed`
+
+Suggested request shapes:
+
+```rust
+enum ProcessStartRequest {
+    Direct(DirectExecSpec),
+    Prepared(PreparedExecSpec),
+}
+
+struct DirectExecSpec {
+    process_id: String,
+    argv: Vec<String>,
+    cwd: PathBuf,
+    env: HashMap<String, String>,
+    arg0: Option<String>,
+    io: ProcessIo,
+}
+
+struct PreparedExecSpec {
+    process_id: String,
+    request: PreparedExecRequest,
+    io: ProcessIo,
+}
+
+enum ProcessIo {
+    Pty { rows: u16, cols: u16 },
+    Pipe { stdin: StdinMode },
+}
+
+enum StdinMode {
+    Open,
+    Closed,
+}
+
+enum TerminateMode {
+    Graceful { timeout_ms: u64 },
+    Force,
+}
+```
+
+Notes:
+
+- `processId` remains a protocol handle, not an OS pid.
+- `wait` is a good generic API because many callers want process completion
+  without manually wiring notifications.
+- `communicate` is also a reasonable API, but it should probably start as a
+  client helper built on top of `write + closeStdin + wait + snapshot`.
+- If an RPC form of `communicate` is added later, it should be a convenience
+  wrapper rather than the primitive execution model.
+
+## Output capping
+
+Even with event streaming, the server should retain a bounded amount of output
+per process so callers can poll, wait, or reconnect without unbounded memory
+growth.
+
+Suggested behavior:
+
+- stream every output chunk live via `process/output`
+- retain capped output per process in memory
+- keep stdout and stderr separately for pipe-backed processes
+- for PTY-backed processes, treat retained output as a single terminal stream
+- expose truncation metadata on snapshots
+
+Suggested snapshot response:
+
+```rust
+struct ProcessSnapshot {
+    stdout: Vec<u8>,
+    stderr: Vec<u8>,
+    terminal: Vec<u8>,
+    truncated: bool,
+    exit_code: Option<i32>,
+    running: bool,
+}
+```
+
+Implementation-wise, the current `HeadTailBuffer` pattern used by unified exec
+is a good fit. The cap should be server config, not request config, so memory
+use stays predictable.
+
+## Sandboxing and networking
+
+### How unified exec does it today
+
+Unified exec does not hand raw command args directly to the PTY layer for tool
+calls. Instead, it:
+
+1. computes approval requirements
+2. chooses a sandbox attempt
+3. applies managed-network policy if needed
+4. transforms `CommandSpec` into `ExecRequest`
+5. spawns from that resolved `ExecRequest`
+
+That split is already valuable and should be preserved.
+
+### Recommended exec-server design
+
+Do not put approval policy into exec-server.
+
+Instead, support two execution modes:
+
+- `Direct`: raw command, intended for orchestrator-side or already-trusted use
+- `Prepared`: already-resolved spawn request, intended for tool-call execution
+
+For tool calls from the LLM side:
+
+1. `core` runs the existing approval + sandbox + managed-network flow
+2. `core` produces a resolved `ExecRequest`
+3. the exec-server client sends `PreparedExecSpec`
+4. exec-server spawns exactly that request and streams process events
+
+For orchestrator-side execution:
+
+1. caller sends `DirectExecSpec`
+2. exec-server spawns directly without running approval or sandbox policy
+
+This gives one generic process API while keeping the policy-sensitive logic in
+the place that already owns it.
+
+### Why not make exec-server own sandbox selection?
+
+That would force exec-server to understand:
+
+- approval policy
+- exec policy / prefix rules
+- managed-network approval flow
+- sandbox retry semantics
+- guardian routing
+- feature-flag-driven sandbox selection
+- platform-specific sandbox helper configuration
+
+That is too opinionated for a reusable process service.
+
+## Optional future server config
+
+If exec-server grows beyond the current prototype, a config object like this
+would be enough:
+
+```rust
+struct ExecServerConfig {
+    shutdown_grace_period_ms: u64,
+    max_processes_per_connection: usize,
+    retained_output_bytes_per_process: usize,
+    allow_direct_exec: bool,
+    allow_prepared_exec: bool,
+}
+```
+
+That keeps policy surface small:
+
+- lifecycle limits live in the server
+- trust and sandbox policy stay with the caller
+
+## Mapping back to LLM-visible events
+
+If unified exec is later backed by exec-server, the `core` client wrapper should
+keep owning the translation into the existing event model:
+
+- `process/start` success -> `ExecCommandBegin`
+- `process/output` -> `ExecCommandOutputDelta`
+- local `process/write` call -> `TerminalInteraction`
+- `process/exited` plus retained transcript -> `ExecCommandEnd`
+
+That preserves the current LLM-facing contract while making the process backend
+swappable.

codex-rs/exec-server/README.md

@@ -0,0 +1,396 @@
+# codex-exec-server
+
+`codex-exec-server` is a small standalone JSON-RPC server for spawning and
+controlling subprocesses through `codex-utils-pty`.
+
+It currently provides:
+
+- a standalone binary: `codex-exec-server`
+- a transport-agnostic server runtime with stdio and websocket entrypoints
+- a Rust client: `ExecServerClient`
+- a direct in-process client mode: `ExecServerClient::connect_in_process`
+- a separate local launch helper: `spawn_local_exec_server`
+- a small protocol module with shared request/response types
+
+This crate is intentionally narrow. It is not wired into the main Codex CLI or
+unified-exec in this PR; it is only the standalone transport layer.
+
+The internal shape is intentionally closer to `app-server` than the first cut:
+
+- transport adapters are separate from the per-connection request processor
+- JSON-RPC route matching is separate from the stateful exec handler
+- the client only speaks the protocol; it does not spawn a server subprocess
+- the client can also bypass the JSON-RPC transport/routing layer in local
+  in-process mode and call the typed handler directly
+- local child-process launch is handled by a separate helper/factory layer
+
+That split is meant to leave reusable seams if exec-server and app-server later
+share transport or JSON-RPC connection utilities. It also keeps the core
+handler testable without the RPC server implementation itself.
+
+Design notes for a likely future integration with unified exec, including
+rough call flow, buffering, and sandboxing boundaries, live in
+[DESIGN.md](./DESIGN.md).
+
+## Transport
+
+The server speaks the same JSON-RPC message shapes over multiple transports.
+
+The standalone binary supports:
+
+- `stdio://` (default)
+- `ws://IP:PORT`
+
+Wire framing:
+
+- stdio: one newline-delimited JSON-RPC message per line on stdin/stdout
+- websocket: one JSON-RPC message per websocket text frame
+
+Like the app-server transport, messages on the wire omit the `"jsonrpc":"2.0"`
+field and use the shared `codex-app-server-protocol` envelope types.
+
+The current protocol version is:
+
+```text
+exec-server.v0
+```
+
+## Lifecycle
+
+Each connection follows this sequence:
+
+1. Send `initialize`.
+2. Wait for the `initialize` response.
+3. Send `initialized`.
+4. Start and manage processes with `process/start`, `process/read`,
+   `process/write`, and `process/terminate`.
+5. Read streaming notifications from `process/output` and
+   `process/exited`.
+
+If the client sends exec methods before completing the `initialize` /
+`initialized` handshake, the server rejects them.
+
+If a connection closes, the server terminates any remaining managed processes
+for that connection.
+
+TODO: add authentication to the `initialize` setup before this is used across a
+trust boundary.
+
+## API
+
+### `initialize`
+
+Initial handshake request.
+
+Request params:
+
+```json
+{
+  "clientName": "my-client"
+}
+```
+
+Response:
+
+```json
+{
+  "protocolVersion": "exec-server.v0"
+}
+```
+
+### `initialized`
+
+Handshake acknowledgement notification sent by the client after a successful
+`initialize` response. Exec methods are rejected until this arrives.
+
+Params are currently ignored. Sending any other client notification method is a
+protocol error.
+
+### `process/start`
+
+Starts a new managed process.
+
+Request params:
+
+```json
+{
+  "processId": "proc-1",
+  "argv": ["bash", "-lc", "printf 'hello\\n'"],
+  "cwd": "/absolute/working/directory",
+  "env": {
+    "PATH": "/usr/bin:/bin"
+  },
+  "tty": true,
+  "arg0": null,
+  "sandbox": null
+}
+```
+
+Field definitions:
+
+- `argv`: command vector. It must be non-empty.
+- `cwd`: absolute working directory used for the child process.
+- `env`: environment variables passed to the child process.
+- `tty`: when `true`, spawn a PTY-backed interactive process; when `false`,
+  spawn a pipe-backed process with closed stdin.
+- `arg0`: optional argv0 override forwarded to `codex-utils-pty`.
+- `sandbox`: optional sandbox config. Omit it for the current direct-spawn
+  behavior. Explicit `{"mode":"none"}` is accepted; `{"mode":"hostDefault"}`
+  is currently rejected until host-local sandbox materialization is wired up.
+
+Response:
+
+```json
+{
+  "processId": "proc-1"
+}
+```
+
+Behavior notes:
+
+- `processId` is chosen by the client and must be unique for the connection.
+- PTY-backed processes accept later writes through `process/write`.
+- Pipe-backed processes are launched with stdin closed and reject writes.
+- Output is streamed asynchronously via `process/output`.
+- Exit is reported asynchronously via `process/exited`.
+
+### `process/write`
+
+Writes raw bytes to a running PTY-backed process stdin.
+
+Request params:
+
+```json
+{
+  "processId": "proc-1",
+  "chunk": "aGVsbG8K"
+}
+```
+
+`chunk` is base64-encoded raw bytes. In the example above it is `hello\n`.
+
+Response:
+
+```json
+{
+  "accepted": true
+}
+```
+
+Behavior notes:
+
+- Writes to an unknown `processId` are rejected.
+- Writes to a non-PTY process are rejected because stdin is already closed.
+
+### `process/read`
+
+Reads retained output from a managed process by sequence number.
+
+Request params:
+
+```json
+{
+  "processId": "proc-1",
+  "afterSeq": 0,
+  "maxBytes": 65536,
+  "waitMs": 250
+}
+```
+
+Response:
+
+```json
+{
+  "chunks": [
+    {
+      "seq": 1,
+      "stream": "pty",
+      "chunk": "aGVsbG8K"
+    }
+  ],
+  "nextSeq": 2,
+  "exited": false,
+  "exitCode": null
+}
+```
+
+Behavior notes:
+
+- Output is retained in bounded server memory so callers can poll without
+  relying only on notifications.
+- `afterSeq` is exclusive: `0` reads from the beginning of the retained buffer.
+- `waitMs` waits briefly for new output or exit if nothing is currently
+  available.
+- Once retained output exceeds the per-process cap, oldest chunks are dropped.
+
+### `process/terminate`
+
+Terminates a running managed process.
+
+Request params:
+
+```json
+{
+  "processId": "proc-1"
+}
+```
+
+Response:
+
+```json
+{
+  "running": true
+}
+```
+
+If the process is already unknown or already removed, the server responds with:
+
+```json
+{
+  "running": false
+}
+```
+
+## Notifications
+
+### `process/output`
+
+Streaming output chunk from a running process.
+
+Params:
+
+```json
+{
+  "processId": "proc-1",
+  "stream": "stdout",
+  "chunk": "aGVsbG8K"
+}
+```
+
+Fields:
+
+- `processId`: process identifier
+- `stream`: `"stdout"`, `"stderr"`, or `"pty"` for PTY-backed processes
+- `chunk`: base64-encoded output bytes
+
+### `process/exited`
+
+Final process exit notification.
+
+Params:
+
+```json
+{
+  "processId": "proc-1",
+  "exitCode": 0
+}
+```
+
+## Errors
+
+The server returns JSON-RPC errors with these codes:
+
+- `-32600`: invalid request
+- `-32602`: invalid params
+- `-32603`: internal error
+
+Typical error cases:
+
+- unknown method
+- malformed params
+- empty `argv`
+- duplicate `processId`
+- writes to unknown processes
+- writes to non-PTY processes
+
+## Rust surface
+
+The crate exports:
+
+- `ExecServerClient`
+- `ExecServerClientConnectOptions`
+- `RemoteExecServerConnectArgs`
+- `ExecServerLaunchCommand`
+- `ExecServerEvent`
+- `SpawnedExecServer`
+- `ExecServerError`
+- `ExecServerTransport`
+- `spawn_local_exec_server(...)`
+- protocol structs such as `ExecParams`, `ExecResponse`,
+  `WriteParams`, `TerminateParams`, `ExecOutputDeltaNotification`, and
+  `ExecExitedNotification`
+- `run_main()` and `run_main_with_transport(...)`
+
+### Binary
+
+Run over stdio:
+
+```text
+codex-exec-server
+```
+
+Run as a websocket server:
+
+```text
+codex-exec-server --listen ws://127.0.0.1:8080
+```
+
+### Client
+
+Connect the client to an existing server transport:
+
+- `ExecServerClient::connect_stdio(...)`
+- `ExecServerClient::connect_websocket(...)`
+- `ExecServerClient::connect_in_process(...)` for a local no-transport mode
+  backed directly by the typed handler
+
+Timeout behavior:
+
+- stdio and websocket clients both enforce an initialize-handshake timeout
+- websocket clients also enforce a connect timeout before the handshake begins
+
+Events:
+
+- `ExecServerClient::event_receiver()` yields `ExecServerEvent`
+- output events include both `stream` (`stdout`, `stderr`, or `pty`) and raw
+  bytes
+- process lifetime is tracked by server notifications such as
+  `process/exited`, not by a client-side process registry
+
+Spawning a local child process is deliberately separate:
+
+- `spawn_local_exec_server(...)`
+
+## Example session
+
+Initialize:
+
+```json
+{"id":1,"method":"initialize","params":{"clientName":"example-client"}}
+{"id":1,"result":{"protocolVersion":"exec-server.v0"}}
+{"method":"initialized","params":{}}
+```
+
+Start a process:
+
+```json
+{"id":2,"method":"process/start","params":{"processId":"proc-1","argv":["bash","-lc","printf 'ready\\n'; while IFS= read -r line; do printf 'echo:%s\\n' \"$line\"; done"],"cwd":"/tmp","env":{"PATH":"/usr/bin:/bin"},"tty":true,"arg0":null}}
+{"id":2,"result":{"processId":"proc-1"}}
+{"method":"process/output","params":{"processId":"proc-1","stream":"pty","chunk":"cmVhZHkK"}}
+```
+
+Write to the process:
+
+```json
+{"id":3,"method":"process/write","params":{"processId":"proc-1","chunk":"aGVsbG8K"}}
+{"id":3,"result":{"accepted":true}}
+{"method":"process/output","params":{"processId":"proc-1","stream":"pty","chunk":"ZWNobzpoZWxsbwo="}}
+```
+
+Terminate it:
+
+```json
+{"id":4,"method":"process/terminate","params":{"processId":"proc-1"}}
+{"id":4,"result":{"running":true}}
+{"method":"process/exited","params":{"processId":"proc-1","exitCode":0}}
+```

codex-rs/exec-server/src/bin/codex-exec-server.rs

@@ -0,0 +1,23 @@
+use clap::Parser;
+use codex_exec_server::ExecServerTransport;
+
+#[derive(Debug, Parser)]
+struct ExecServerArgs {
+    /// Transport endpoint URL. Supported values: `stdio://` (default),
+    /// `ws://IP:PORT`.
+    #[arg(
+        long = "listen",
+        value_name = "URL",
+        default_value = ExecServerTransport::DEFAULT_LISTEN_URL
+    )]
+    listen: ExecServerTransport,
+}
+
+#[tokio::main]
+async fn main() {
+    let args = ExecServerArgs::parse();
+    if let Err(err) = codex_exec_server::run_main_with_transport(args.listen).await {
+        eprintln!("{err}");
+        std::process::exit(1);
+    }
+}

codex-rs/exec-server/src/client.rs

@@ -0,0 +1,717 @@
+use std::collections::HashMap;
+use std::future::Future;
+use std::sync::Arc;
+use std::sync::atomic::AtomicI64;
+use std::sync::atomic::Ordering;
+use std::time::Duration;
+
+use codex_app_server_protocol::FsCopyParams;
+use codex_app_server_protocol::FsCopyResponse;
+use codex_app_server_protocol::FsCreateDirectoryParams;
+use codex_app_server_protocol::FsCreateDirectoryResponse;
+use codex_app_server_protocol::FsGetMetadataParams;
+use codex_app_server_protocol::FsGetMetadataResponse;
+use codex_app_server_protocol::FsReadDirectoryParams;
+use codex_app_server_protocol::FsReadDirectoryResponse;
+use codex_app_server_protocol::FsReadFileParams;
+use codex_app_server_protocol::FsReadFileResponse;
+use codex_app_server_protocol::FsRemoveParams;
+use codex_app_server_protocol::FsRemoveResponse;
+use codex_app_server_protocol::FsWriteFileParams;
+use codex_app_server_protocol::FsWriteFileResponse;
+use codex_app_server_protocol::JSONRPCError;
+use codex_app_server_protocol::JSONRPCErrorError;
+use codex_app_server_protocol::JSONRPCMessage;
+use codex_app_server_protocol::JSONRPCNotification;
+use codex_app_server_protocol::JSONRPCResponse;
+use codex_app_server_protocol::RequestId;
+use serde::Serialize;
+use serde_json::Value;
+use tokio::io::AsyncRead;
+use tokio::io::AsyncWrite;
+use tokio::sync::Mutex;
+use tokio::sync::broadcast;
+use tokio::sync::mpsc;
+use tokio::sync::oneshot;
+use tokio::task::JoinHandle;
+use tokio::time::timeout;
+use tokio_tungstenite::connect_async;
+use tracing::debug;
+use tracing::warn;
+
+use crate::client_api::ExecServerClientConnectOptions;
+use crate::client_api::ExecServerEvent;
+use crate::client_api::RemoteExecServerConnectArgs;
+use crate::connection::JsonRpcConnection;
+use crate::connection::JsonRpcConnectionEvent;
+use crate::protocol::EXEC_EXITED_METHOD;
+use crate::protocol::EXEC_METHOD;
+use crate::protocol::EXEC_OUTPUT_DELTA_METHOD;
+use crate::protocol::EXEC_READ_METHOD;
+use crate::protocol::EXEC_TERMINATE_METHOD;
+use crate::protocol::EXEC_WRITE_METHOD;
+use crate::protocol::ExecExitedNotification;
+use crate::protocol::ExecOutputDeltaNotification;
+use crate::protocol::ExecParams;
+use crate::protocol::ExecResponse;
+use crate::protocol::FS_COPY_METHOD;
+use crate::protocol::FS_CREATE_DIRECTORY_METHOD;
+use crate::protocol::FS_GET_METADATA_METHOD;
+use crate::protocol::FS_READ_DIRECTORY_METHOD;
+use crate::protocol::FS_READ_FILE_METHOD;
+use crate::protocol::FS_REMOVE_METHOD;
+use crate::protocol::FS_WRITE_FILE_METHOD;
+use crate::protocol::INITIALIZE_METHOD;
+use crate::protocol::INITIALIZED_METHOD;
+use crate::protocol::InitializeResponse;
+use crate::protocol::ReadParams;
+use crate::protocol::ReadResponse;
+use crate::protocol::TerminateParams;
+use crate::protocol::TerminateResponse;
+use crate::protocol::WriteParams;
+use crate::protocol::WriteResponse;
+use crate::server::ExecServerOutboundMessage;
+use crate::server::ExecServerServerNotification;
+
+mod jsonrpc_backend;
+mod local_backend;
+#[cfg(test)]
+mod process;
+use jsonrpc_backend::JsonRpcBackend;
+use local_backend::LocalBackend;
+#[cfg(test)]
+use process::ExecServerOutput;
+#[cfg(test)]
+use process::ExecServerProcess;
+#[cfg(test)]
+use process::RemoteProcessStatus;
+
+impl Default for ExecServerClientConnectOptions {
+    fn default() -> Self {
+        Self {
+            client_name: "codex-core".to_string(),
+            initialize_timeout: INITIALIZE_TIMEOUT,
+        }
+    }
+}
+
+impl From<RemoteExecServerConnectArgs> for ExecServerClientConnectOptions {
+    fn from(value: RemoteExecServerConnectArgs) -> Self {
+        Self {
+            client_name: value.client_name,
+            initialize_timeout: value.initialize_timeout,
+        }
+    }
+}
+
+const CONNECT_TIMEOUT: Duration = Duration::from_secs(10);
+const INITIALIZE_TIMEOUT: Duration = Duration::from_secs(10);
+
+impl RemoteExecServerConnectArgs {
+    pub fn new(websocket_url: String, client_name: String) -> Self {
+        Self {
+            websocket_url,
+            client_name,
+            connect_timeout: CONNECT_TIMEOUT,
+            initialize_timeout: INITIALIZE_TIMEOUT,
+        }
+    }
+}
+
+type PendingRequest = oneshot::Sender<Result<Value, JSONRPCErrorError>>;
+
+enum ClientBackend {
+    JsonRpc(JsonRpcBackend),
+    InProcess(LocalBackend),
+}
+
+impl ClientBackend {
+    fn as_local(&self) -> Option<&LocalBackend> {
+        match self {
+            ClientBackend::JsonRpc(_) => None,
+            ClientBackend::InProcess(backend) => Some(backend),
+        }
+    }
+
+    fn as_jsonrpc(&self) -> Option<&JsonRpcBackend> {
+        match self {
+            ClientBackend::JsonRpc(backend) => Some(backend),
+            ClientBackend::InProcess(_) => None,
+        }
+    }
+}
+
+struct Inner {
+    backend: ClientBackend,
+    pending: Mutex<HashMap<RequestId, PendingRequest>>,
+    events_tx: broadcast::Sender<ExecServerEvent>,
+    next_request_id: AtomicI64,
+    transport_tasks: Vec<JoinHandle<()>>,
+    reader_task: JoinHandle<()>,
+}
+
+impl Drop for Inner {
+    fn drop(&mut self) {
+        if let Some(backend) = self.backend.as_local()
+            && let Ok(handle) = tokio::runtime::Handle::try_current()
+        {
+            let backend = backend.clone();
+            handle.spawn(async move {
+                backend.shutdown().await;
+            });
+        }
+        for task in &self.transport_tasks {
+            task.abort();
+        }
+        self.reader_task.abort();
+    }
+}
+
+#[derive(Clone)]
+pub struct ExecServerClient {
+    inner: Arc<Inner>,
+}
+
+#[derive(Debug, thiserror::Error)]
+pub enum ExecServerError {
+    #[error("failed to spawn exec-server: {0}")]
+    Spawn(#[source] std::io::Error),
+    #[error("timed out connecting to exec-server websocket `{url}` after {timeout:?}")]
+    WebSocketConnectTimeout { url: String, timeout: Duration },
+    #[error("failed to connect to exec-server websocket `{url}`: {source}")]
+    WebSocketConnect {
+        url: String,
+        #[source]
+        source: tokio_tungstenite::tungstenite::Error,
+    },
+    #[error("timed out waiting for exec-server initialize handshake after {timeout:?}")]
+    InitializeTimedOut { timeout: Duration },
+    #[error("exec-server transport closed")]
+    Closed,
+    #[error("failed to serialize or deserialize exec-server JSON: {0}")]
+    Json(#[from] serde_json::Error),
+    #[error("exec-server protocol error: {0}")]
+    Protocol(String),
+    #[error("exec-server rejected request ({code}): {message}")]
+    Server { code: i64, message: String },
+}
+
+impl ExecServerClient {
+    pub async fn connect_in_process(
+        options: ExecServerClientConnectOptions,
+    ) -> Result<Self, ExecServerError> {
+        let (outbound_tx, mut outgoing_rx) = mpsc::channel::<ExecServerOutboundMessage>(256);
+        let backend = LocalBackend::new(crate::server::ExecServerHandler::new(outbound_tx));
+
+        let inner = Arc::new_cyclic(|weak| {
+            let weak = weak.clone();
+            let reader_task = tokio::spawn(async move {
+                while let Some(message) = outgoing_rx.recv().await {
+                    if let Some(inner) = weak.upgrade()
+                        && let Err(err) = handle_in_process_outbound_message(&inner, message).await
+                    {
+                        warn!(
+                            "in-process exec-server client closing after unexpected response: {err}"
+                        );
+                        handle_transport_shutdown(&inner).await;
+                        return;
+                    }
+                }
+
+                if let Some(inner) = weak.upgrade() {
+                    handle_transport_shutdown(&inner).await;
+                }
+            });
+
+            Inner {
+                backend: ClientBackend::InProcess(backend),
+                pending: Mutex::new(HashMap::new()),
+                events_tx: broadcast::channel(256).0,
+                next_request_id: AtomicI64::new(1),
+                transport_tasks: Vec::new(),
+                reader_task,
+            }
+        });
+
+        let client = Self { inner };
+        client.initialize(options).await?;
+        Ok(client)
+    }
+
+    pub async fn connect_stdio<R, W>(
+        stdin: W,
+        stdout: R,
+        options: ExecServerClientConnectOptions,
+    ) -> Result<Self, ExecServerError>
+    where
+        R: AsyncRead + Unpin + Send + 'static,
+        W: AsyncWrite + Unpin + Send + 'static,
+    {
+        Self::connect(
+            JsonRpcConnection::from_stdio(stdout, stdin, "exec-server stdio".to_string()),
+            options,
+        )
+        .await
+    }
+
+    pub async fn connect_websocket(
+        args: RemoteExecServerConnectArgs,
+    ) -> Result<Self, ExecServerError> {
+        let websocket_url = args.websocket_url.clone();
+        let connect_timeout = args.connect_timeout;
+        let (stream, _) = timeout(connect_timeout, connect_async(websocket_url.as_str()))
+            .await
+            .map_err(|_| ExecServerError::WebSocketConnectTimeout {
+                url: websocket_url.clone(),
+                timeout: connect_timeout,
+            })?
+            .map_err(|source| ExecServerError::WebSocketConnect {
+                url: websocket_url.clone(),
+                source,
+            })?;
+
+        Self::connect(
+            JsonRpcConnection::from_websocket(
+                stream,
+                format!("exec-server websocket {websocket_url}"),
+            ),
+            args.into(),
+        )
+        .await
+    }
+
+    async fn connect(
+        connection: JsonRpcConnection,
+        options: ExecServerClientConnectOptions,
+    ) -> Result<Self, ExecServerError> {
+        let (write_tx, mut incoming_rx, transport_tasks) = connection.into_parts();
+        let inner = Arc::new_cyclic(|weak| {
+            let weak = weak.clone();
+            let reader_task = tokio::spawn(async move {
+                while let Some(event) = incoming_rx.recv().await {
+                    match event {
+                        JsonRpcConnectionEvent::Message(message) => {
+                            if let Some(inner) = weak.upgrade()
+                                && let Err(err) = handle_server_message(&inner, message).await
+                            {
+                                warn!("exec-server client closing after protocol error: {err}");
+                                handle_transport_shutdown(&inner).await;
+                                return;
+                            }
+                        }
+                        JsonRpcConnectionEvent::Disconnected { reason } => {
+                            if let Some(reason) = reason {
+                                warn!("exec-server client transport disconnected: {reason}");
+                            }
+                            if let Some(inner) = weak.upgrade() {
+                                handle_transport_shutdown(&inner).await;
+                            }
+                            return;
+                        }
+                    }
+                }
+
+                if let Some(inner) = weak.upgrade() {
+                    handle_transport_shutdown(&inner).await;
+                }
+            });
+
+            Inner {
+                backend: ClientBackend::JsonRpc(JsonRpcBackend::new(write_tx)),
+                pending: Mutex::new(HashMap::new()),
+                events_tx: broadcast::channel(256).0,
+                next_request_id: AtomicI64::new(1),
+                transport_tasks,
+                reader_task,
+            }
+        });
+
+        let client = Self { inner };
+        client.initialize(options).await?;
+        Ok(client)
+    }
+
+    pub fn event_receiver(&self) -> broadcast::Receiver<ExecServerEvent> {
+        self.inner.events_tx.subscribe()
+    }
+
+    #[cfg(test)]
+    async fn start_process(
+        &self,
+        params: ExecParams,
+    ) -> Result<ExecServerProcess, ExecServerError> {
+        let response = self.exec(params).await?;
+        let process_id = response.process_id;
+        let status = Arc::new(RemoteProcessStatus::new());
+        let (output_tx, output_rx) = broadcast::channel(256);
+        let mut events_rx = self.event_receiver();
+        let status_watcher = Arc::clone(&status);
+        let watch_process_id = process_id.clone();
+        tokio::spawn(async move {
+            while let Ok(event) = events_rx.recv().await {
+                match event {
+                    ExecServerEvent::OutputDelta(notification)
+                        if notification.process_id == watch_process_id =>
+                    {
+                        let _ = output_tx.send(ExecServerOutput {
+                            stream: notification.stream,
+                            chunk: notification.chunk.into_inner(),
+                        });
+                    }
+                    ExecServerEvent::Exited(notification)
+                        if notification.process_id == watch_process_id =>
+                    {
+                        status_watcher.mark_exited(Some(notification.exit_code));
+                        break;
+                    }
+                    ExecServerEvent::OutputDelta(_) | ExecServerEvent::Exited(_) => {}
+                }
+            }
+        });
+
+        Ok(ExecServerProcess {
+            process_id,
+            output_rx,
+            status,
+            client: self.clone(),
+        })
+    }
+
+    pub async fn exec(&self, params: ExecParams) -> Result<ExecResponse, ExecServerError> {
+        self.request_or_local(EXEC_METHOD, params, |backend, params| async move {
+            backend.exec(params).await
+        })
+        .await
+    }
+
+    pub async fn read(&self, params: ReadParams) -> Result<ReadResponse, ExecServerError> {
+        self.request_or_local(EXEC_READ_METHOD, params, |backend, params| async move {
+            backend.exec_read(params).await
+        })
+        .await
+    }
+
+    pub async fn write(
+        &self,
+        process_id: &str,
+        chunk: Vec<u8>,
+    ) -> Result<WriteResponse, ExecServerError> {
+        let params = WriteParams {
+            process_id: process_id.to_string(),
+            chunk: chunk.into(),
+        };
+        self.request_or_local(EXEC_WRITE_METHOD, params, |backend, params| async move {
+            backend.exec_write(params).await
+        })
+        .await
+    }
+
+    pub async fn terminate(&self, process_id: &str) -> Result<TerminateResponse, ExecServerError> {
+        let params = TerminateParams {
+            process_id: process_id.to_string(),
+        };
+        self.request_or_local(
+            EXEC_TERMINATE_METHOD,
+            params,
+            |backend, params| async move { backend.terminate(params).await },
+        )
+        .await
+    }
+
+    pub async fn fs_read_file(
+        &self,
+        params: FsReadFileParams,
+    ) -> Result<FsReadFileResponse, ExecServerError> {
+        self.request_or_local(FS_READ_FILE_METHOD, params, |backend, params| async move {
+            backend.fs_read_file(params).await
+        })
+        .await
+    }
+
+    pub async fn fs_write_file(
+        &self,
+        params: FsWriteFileParams,
+    ) -> Result<FsWriteFileResponse, ExecServerError> {
+        self.request_or_local(FS_WRITE_FILE_METHOD, params, |backend, params| async move {
+            backend.fs_write_file(params).await
+        })
+        .await
+    }
+
+    pub async fn fs_create_directory(
+        &self,
+        params: FsCreateDirectoryParams,
+    ) -> Result<FsCreateDirectoryResponse, ExecServerError> {
+        self.request_or_local(
+            FS_CREATE_DIRECTORY_METHOD,
+            params,
+            |backend, params| async move { backend.fs_create_directory(params).await },
+        )
+        .await
+    }
+
+    pub async fn fs_get_metadata(
+        &self,
+        params: FsGetMetadataParams,
+    ) -> Result<FsGetMetadataResponse, ExecServerError> {
+        self.request_or_local(
+            FS_GET_METADATA_METHOD,
+            params,
+            |backend, params| async move { backend.fs_get_metadata(params).await },
+        )
+        .await
+    }
+
+    pub async fn fs_read_directory(
+        &self,
+        params: FsReadDirectoryParams,
+    ) -> Result<FsReadDirectoryResponse, ExecServerError> {
+        self.request_or_local(
+            FS_READ_DIRECTORY_METHOD,
+            params,
+            |backend, params| async move { backend.fs_read_directory(params).await },
+        )
+        .await
+    }
+
+    pub async fn fs_remove(
+        &self,
+        params: FsRemoveParams,
+    ) -> Result<FsRemoveResponse, ExecServerError> {
+        self.request_or_local(FS_REMOVE_METHOD, params, |backend, params| async move {
+            backend.fs_remove(params).await
+        })
+        .await
+    }
+
+    pub async fn fs_copy(&self, params: FsCopyParams) -> Result<FsCopyResponse, ExecServerError> {
+        self.request_or_local(FS_COPY_METHOD, params, |backend, params| async move {
+            backend.fs_copy(params).await
+        })
+        .await
+    }
+
+    async fn initialize(
+        &self,
+        options: ExecServerClientConnectOptions,
+    ) -> Result<(), ExecServerError> {
+        let ExecServerClientConnectOptions {
+            client_name,
+            initialize_timeout,
+        } = options;
+        timeout(initialize_timeout, async {
+            if let Some(backend) = self.inner.backend.as_local() {
+                backend.initialize().await?;
+            } else {
+                let params = crate::protocol::InitializeParams { client_name };
+                let _: InitializeResponse = self
+                    .send_pending_request(INITIALIZE_METHOD, &params)
+                    .await?;
+            }
+            self.notify(INITIALIZED_METHOD, &serde_json::json!({}))
+                .await
+        })
+        .await
+        .map_err(|_| ExecServerError::InitializeTimedOut {
+            timeout: initialize_timeout,
+        })?
+    }
+
+    async fn notify<P: Serialize>(&self, method: &str, params: &P) -> Result<(), ExecServerError> {
+        match &self.inner.backend {
+            ClientBackend::JsonRpc(backend) => backend.notify(method, params).await,
+            ClientBackend::InProcess(backend) => backend.notify(method).await,
+        }
+    }
+
+    fn next_request_id(&self) -> RequestId {
+        RequestId::Integer(self.inner.next_request_id.fetch_add(1, Ordering::SeqCst))
+    }
+
+    async fn send_pending_request<P, T>(
+        &self,
+        method: &str,
+        params: &P,
+    ) -> Result<T, ExecServerError>
+    where
+        P: Serialize,
+        T: serde::de::DeserializeOwned,
+    {
+        let request_id = self.next_request_id();
+        let (response_tx, response_rx) = oneshot::channel();
+        self.inner
+            .pending
+            .lock()
+            .await
+            .insert(request_id.clone(), response_tx);
+        let Some(backend) = self.inner.backend.as_jsonrpc() else {
+            unreachable!("in-process requests return before JSON-RPC setup");
+        };
+        let send_result = backend
+            .send_request(request_id.clone(), method, params)
+            .await;
+        self.finish_request(request_id, send_result, response_rx)
+            .await
+    }
+
+    async fn request_or_local<P, T, Fut>(
+        &self,
+        method: &str,
+        params: P,
+        call_local: impl FnOnce(LocalBackend, P) -> Fut,
+    ) -> Result<T, ExecServerError>
+    where
+        P: Serialize,
+        T: serde::de::DeserializeOwned,
+        Fut: Future<Output = Result<T, ExecServerError>>,
+    {
+        if let Some(backend) = self.inner.backend.as_local() {
+            return call_local(backend.clone(), params).await;
+        }
+
+        self.send_pending_request(method, &params).await
+    }
+
+    async fn finish_request<T>(
+        &self,
+        request_id: RequestId,
+        send_result: Result<(), ExecServerError>,
+        response_rx: oneshot::Receiver<Result<Value, JSONRPCErrorError>>,
+    ) -> Result<T, ExecServerError>
+    where
+        T: serde::de::DeserializeOwned,
+    {
+        if let Err(err) = send_result {
+            self.inner.pending.lock().await.remove(&request_id);
+            return Err(err);
+        }
+        let response = receive_json_response(response_rx).await?;
+        Ok(serde_json::from_value(response)?)
+    }
+}
+
+async fn receive_json_response(
+    response_rx: oneshot::Receiver<Result<Value, JSONRPCErrorError>>,
+) -> Result<Value, ExecServerError> {
+    let result = response_rx.await.map_err(|_| ExecServerError::Closed)?;
+    match result {
+        Ok(response) => Ok(response),
+        Err(error) => Err(ExecServerError::Server {
+            code: error.code,
+            message: error.message,
+        }),
+    }
+}
+
+fn server_result_to_client<T>(result: Result<T, JSONRPCErrorError>) -> Result<T, ExecServerError> {
+    match result {
+        Ok(response) => Ok(response),
+        Err(error) => Err(ExecServerError::Server {
+            code: error.code,
+            message: error.message,
+        }),
+    }
+}
+
+async fn handle_in_process_outbound_message(
+    inner: &Arc<Inner>,
+    message: ExecServerOutboundMessage,
+) -> Result<(), ExecServerError> {
+    match message {
+        ExecServerOutboundMessage::Response { .. } | ExecServerOutboundMessage::Error { .. } => {
+            return Err(ExecServerError::Protocol(
+                "unexpected in-process RPC response".to_string(),
+            ));
+        }
+        ExecServerOutboundMessage::Notification(notification) => {
+            handle_in_process_notification(inner, notification).await;
+        }
+    }
+
+    Ok(())
+}
+
+async fn handle_in_process_notification(
+    inner: &Arc<Inner>,
+    notification: ExecServerServerNotification,
+) {
+    match notification {
+        ExecServerServerNotification::OutputDelta(params) => {
+            let _ = inner.events_tx.send(ExecServerEvent::OutputDelta(params));
+        }
+        ExecServerServerNotification::Exited(params) => {
+            let _ = inner.events_tx.send(ExecServerEvent::Exited(params));
+        }
+    }
+}
+
+async fn handle_server_message(
+    inner: &Arc<Inner>,
+    message: JSONRPCMessage,
+) -> Result<(), ExecServerError> {
+    match message {
+        JSONRPCMessage::Response(JSONRPCResponse { id, result }) => {
+            if let Some(pending) = inner.pending.lock().await.remove(&id) {
+                let _ = pending.send(Ok(result));
+            }
+        }
+        JSONRPCMessage::Error(JSONRPCError { id, error }) => {
+            if let Some(pending) = inner.pending.lock().await.remove(&id) {
+                let _ = pending.send(Err(error));
+            }
+        }
+        JSONRPCMessage::Notification(notification) => {
+            handle_server_notification(inner, notification).await?;
+        }
+        JSONRPCMessage::Request(request) => {
+            return Err(ExecServerError::Protocol(format!(
+                "unexpected exec-server request from remote server: {}",
+                request.method
+            )));
+        }
+    }
+
+    Ok(())
+}
+
+async fn handle_server_notification(
+    inner: &Arc<Inner>,
+    notification: JSONRPCNotification,
+) -> Result<(), ExecServerError> {
+    match notification.method.as_str() {
+        EXEC_OUTPUT_DELTA_METHOD => {
+            let params: ExecOutputDeltaNotification =
+                serde_json::from_value(notification.params.unwrap_or(Value::Null))?;
+            let _ = inner.events_tx.send(ExecServerEvent::OutputDelta(params));
+        }
+        EXEC_EXITED_METHOD => {
+            let params: ExecExitedNotification =
+                serde_json::from_value(notification.params.unwrap_or(Value::Null))?;
+            let _ = inner.events_tx.send(ExecServerEvent::Exited(params));
+        }
+        other => {
+            debug!("ignoring unknown exec-server notification: {other}");
+        }
+    }
+    Ok(())
+}
+
+async fn handle_transport_shutdown(inner: &Arc<Inner>) {
+    let pending = {
+        let mut pending = inner.pending.lock().await;
+        pending
+            .drain()
+            .map(|(_, pending)| pending)
+            .collect::<Vec<_>>()
+    };
+    for pending in pending {
+        let _ = pending.send(Err(JSONRPCErrorError {
+            code: -32000,
+            data: None,
+            message: "exec-server transport closed".to_string(),
+        }));
+    }
+}
+
+#[cfg(test)]
+mod tests;

codex-rs/exec-server/src/client/jsonrpc_backend.rs

@@ -0,0 +1,51 @@
+use codex_app_server_protocol::JSONRPCMessage;
+use codex_app_server_protocol::JSONRPCNotification;
+use codex_app_server_protocol::JSONRPCRequest;
+use codex_app_server_protocol::RequestId;
+use serde::Serialize;
+use tokio::sync::mpsc;
+
+use super::ExecServerError;
+
+pub(super) struct JsonRpcBackend {
+    write_tx: mpsc::Sender<JSONRPCMessage>,
+}
+
+impl JsonRpcBackend {
+    pub(super) fn new(write_tx: mpsc::Sender<JSONRPCMessage>) -> Self {
+        Self { write_tx }
+    }
+
+    pub(super) async fn notify<P: Serialize>(
+        &self,
+        method: &str,
+        params: &P,
+    ) -> Result<(), ExecServerError> {
+        let params = serde_json::to_value(params)?;
+        self.write_tx
+            .send(JSONRPCMessage::Notification(JSONRPCNotification {
+                method: method.to_string(),
+                params: Some(params),
+            }))
+            .await
+            .map_err(|_| ExecServerError::Closed)
+    }
+
+    pub(super) async fn send_request<P: Serialize>(
+        &self,
+        request_id: RequestId,
+        method: &str,
+        params: &P,
+    ) -> Result<(), ExecServerError> {
+        let params = serde_json::to_value(params)?;
+        self.write_tx
+            .send(JSONRPCMessage::Request(JSONRPCRequest {
+                id: request_id,
+                method: method.to_string(),
+                params: Some(params),
+                trace: None,
+            }))
+            .await
+            .map_err(|_| ExecServerError::Closed)
+    }
+}

codex-rs/exec-server/src/client/local_backend.rs

@@ -0,0 +1,141 @@
+use std::sync::Arc;
+
+use codex_app_server_protocol::FsCopyParams;
+use codex_app_server_protocol::FsCopyResponse;
+use codex_app_server_protocol::FsCreateDirectoryParams;
+use codex_app_server_protocol::FsCreateDirectoryResponse;
+use codex_app_server_protocol::FsGetMetadataParams;
+use codex_app_server_protocol::FsGetMetadataResponse;
+use codex_app_server_protocol::FsReadDirectoryParams;
+use codex_app_server_protocol::FsReadDirectoryResponse;
+use codex_app_server_protocol::FsReadFileParams;
+use codex_app_server_protocol::FsReadFileResponse;
+use codex_app_server_protocol::FsRemoveParams;
+use codex_app_server_protocol::FsRemoveResponse;
+use codex_app_server_protocol::FsWriteFileParams;
+use codex_app_server_protocol::FsWriteFileResponse;
+use tokio::sync::Mutex;
+
+use crate::protocol::ExecParams;
+use crate::protocol::ExecResponse;
+use crate::protocol::INITIALIZED_METHOD;
+use crate::protocol::InitializeResponse;
+use crate::protocol::ReadParams;
+use crate::protocol::ReadResponse;
+use crate::protocol::TerminateParams;
+use crate::protocol::TerminateResponse;
+use crate::protocol::WriteParams;
+use crate::protocol::WriteResponse;
+use crate::server::ExecServerHandler;
+
+use super::ExecServerError;
+use super::server_result_to_client;
+
+#[derive(Clone)]
+pub(super) struct LocalBackend {
+    handler: Arc<Mutex<ExecServerHandler>>,
+}
+
+impl LocalBackend {
+    pub(super) fn new(handler: ExecServerHandler) -> Self {
+        Self {
+            handler: Arc::new(Mutex::new(handler)),
+        }
+    }
+
+    pub(super) async fn shutdown(&self) {
+        self.handler.lock().await.shutdown().await;
+    }
+
+    pub(super) async fn initialize(&self) -> Result<InitializeResponse, ExecServerError> {
+        server_result_to_client(self.handler.lock().await.initialize())
+    }
+
+    pub(super) async fn notify(&self, method: &str) -> Result<(), ExecServerError> {
+        match method {
+            INITIALIZED_METHOD => self
+                .handler
+                .lock()
+                .await
+                .initialized()
+                .map_err(ExecServerError::Protocol),
+            other => Err(ExecServerError::Protocol(format!(
+                "unsupported in-process notification method `{other}`"
+            ))),
+        }
+    }
+
+    pub(super) async fn exec(&self, params: ExecParams) -> Result<ExecResponse, ExecServerError> {
+        server_result_to_client(self.handler.lock().await.exec(params).await)
+    }
+
+    pub(super) async fn exec_read(
+        &self,
+        params: ReadParams,
+    ) -> Result<ReadResponse, ExecServerError> {
+        server_result_to_client(self.handler.lock().await.exec_read(params).await)
+    }
+
+    pub(super) async fn exec_write(
+        &self,
+        params: WriteParams,
+    ) -> Result<WriteResponse, ExecServerError> {
+        server_result_to_client(self.handler.lock().await.exec_write(params).await)
+    }
+
+    pub(super) async fn terminate(
+        &self,
+        params: TerminateParams,
+    ) -> Result<TerminateResponse, ExecServerError> {
+        server_result_to_client(self.handler.lock().await.terminate(params).await)
+    }
+
+    pub(super) async fn fs_read_file(
+        &self,
+        params: FsReadFileParams,
+    ) -> Result<FsReadFileResponse, ExecServerError> {
+        server_result_to_client(self.handler.lock().await.fs_read_file(params).await)
+    }
+
+    pub(super) async fn fs_write_file(
+        &self,
+        params: FsWriteFileParams,
+    ) -> Result<FsWriteFileResponse, ExecServerError> {
+        server_result_to_client(self.handler.lock().await.fs_write_file(params).await)
+    }
+
+    pub(super) async fn fs_create_directory(
+        &self,
+        params: FsCreateDirectoryParams,
+    ) -> Result<FsCreateDirectoryResponse, ExecServerError> {
+        server_result_to_client(self.handler.lock().await.fs_create_directory(params).await)
+    }
+
+    pub(super) async fn fs_get_metadata(
+        &self,
+        params: FsGetMetadataParams,
+    ) -> Result<FsGetMetadataResponse, ExecServerError> {
+        server_result_to_client(self.handler.lock().await.fs_get_metadata(params).await)
+    }
+
+    pub(super) async fn fs_read_directory(
+        &self,
+        params: FsReadDirectoryParams,
+    ) -> Result<FsReadDirectoryResponse, ExecServerError> {
+        server_result_to_client(self.handler.lock().await.fs_read_directory(params).await)
+    }
+
+    pub(super) async fn fs_remove(
+        &self,
+        params: FsRemoveParams,
+    ) -> Result<FsRemoveResponse, ExecServerError> {
+        server_result_to_client(self.handler.lock().await.fs_remove(params).await)
+    }
+
+    pub(super) async fn fs_copy(
+        &self,
+        params: FsCopyParams,
+    ) -> Result<FsCopyResponse, ExecServerError> {
+        server_result_to_client(self.handler.lock().await.fs_copy(params).await)
+    }
+}

codex-rs/exec-server/src/client/process.rs

@@ -0,0 +1,72 @@
+use std::sync::Arc;
+use std::sync::Mutex as StdMutex;
+use std::sync::atomic::AtomicBool;
+use std::sync::atomic::Ordering;
+
+use tokio::sync::broadcast;
+
+use super::ExecServerClient;
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub(super) struct ExecServerOutput {
+    pub(super) stream: crate::protocol::ExecOutputStream,
+    pub(super) chunk: Vec<u8>,
+}
+
+pub(super) struct ExecServerProcess {
+    pub(super) process_id: String,
+    pub(super) output_rx: broadcast::Receiver<ExecServerOutput>,
+    pub(super) status: Arc<RemoteProcessStatus>,
+    pub(super) client: ExecServerClient,
+}
+
+impl ExecServerProcess {
+    pub(super) fn output_receiver(&self) -> broadcast::Receiver<ExecServerOutput> {
+        self.output_rx.resubscribe()
+    }
+
+    pub(super) fn has_exited(&self) -> bool {
+        self.status.has_exited()
+    }
+
+    pub(super) fn exit_code(&self) -> Option<i32> {
+        self.status.exit_code()
+    }
+
+    pub(super) fn terminate(&self) {
+        let client = self.client.clone();
+        let process_id = self.process_id.clone();
+        tokio::spawn(async move {
+            let _ = client.terminate(&process_id).await;
+        });
+    }
+}
+
+pub(super) struct RemoteProcessStatus {
+    exited: AtomicBool,
+    exit_code: StdMutex<Option<i32>>,
+}
+
+impl RemoteProcessStatus {
+    pub(super) fn new() -> Self {
+        Self {
+            exited: AtomicBool::new(false),
+            exit_code: StdMutex::new(None),
+        }
+    }
+
+    pub(super) fn has_exited(&self) -> bool {
+        self.exited.load(Ordering::SeqCst)
+    }
+
+    pub(super) fn exit_code(&self) -> Option<i32> {
+        self.exit_code.lock().ok().and_then(|guard| *guard)
+    }
+
+    pub(super) fn mark_exited(&self, exit_code: Option<i32>) {
+        self.exited.store(true, Ordering::SeqCst);
+        if let Ok(mut guard) = self.exit_code.lock() {
+            *guard = exit_code;
+        }
+    }
+}

codex-rs/exec-server/src/client/tests.rs

@@ -0,0 +1,888 @@
+use std::collections::HashMap;
+use std::time::Duration;
+
+use pretty_assertions::assert_eq;
+use tokio::io::AsyncBufReadExt;
+use tokio::io::AsyncWriteExt;
+use tokio::io::BufReader;
+use tokio::time::timeout;
+
+use super::ExecServerClient;
+use super::ExecServerClientConnectOptions;
+use super::ExecServerError;
+use super::ExecServerOutput;
+use crate::protocol::EXEC_METHOD;
+use crate::protocol::EXEC_OUTPUT_DELTA_METHOD;
+use crate::protocol::EXEC_TERMINATE_METHOD;
+use crate::protocol::ExecOutputStream;
+use crate::protocol::ExecParams;
+use crate::protocol::INITIALIZE_METHOD;
+use crate::protocol::INITIALIZED_METHOD;
+use crate::protocol::PROTOCOL_VERSION;
+use crate::protocol::ReadParams;
+use codex_app_server_protocol::JSONRPCError;
+use codex_app_server_protocol::JSONRPCErrorError;
+use codex_app_server_protocol::JSONRPCMessage;
+use codex_app_server_protocol::JSONRPCNotification;
+use codex_app_server_protocol::JSONRPCRequest;
+use codex_app_server_protocol::JSONRPCResponse;
+
+fn test_options() -> ExecServerClientConnectOptions {
+    ExecServerClientConnectOptions {
+        client_name: "test-client".to_string(),
+        initialize_timeout: Duration::from_secs(1),
+    }
+}
+
+async fn read_jsonrpc_line<R>(lines: &mut tokio::io::Lines<BufReader<R>>) -> JSONRPCMessage
+where
+    R: tokio::io::AsyncRead + Unpin,
+{
+    let next_line = timeout(Duration::from_secs(1), lines.next_line()).await;
+    let line_result = match next_line {
+        Ok(line_result) => line_result,
+        Err(err) => panic!("timed out waiting for JSON-RPC line: {err}"),
+    };
+    let maybe_line = match line_result {
+        Ok(maybe_line) => maybe_line,
+        Err(err) => panic!("failed to read JSON-RPC line: {err}"),
+    };
+    let line = match maybe_line {
+        Some(line) => line,
+        None => panic!("server connection closed before JSON-RPC line arrived"),
+    };
+    match serde_json::from_str::<JSONRPCMessage>(&line) {
+        Ok(message) => message,
+        Err(err) => panic!("failed to parse JSON-RPC line: {err}"),
+    }
+}
+
+async fn write_jsonrpc_line<W>(writer: &mut W, message: JSONRPCMessage)
+where
+    W: tokio::io::AsyncWrite + Unpin,
+{
+    let encoded = match serde_json::to_string(&message) {
+        Ok(encoded) => encoded,
+        Err(err) => panic!("failed to encode JSON-RPC message: {err}"),
+    };
+    if let Err(err) = writer.write_all(format!("{encoded}\n").as_bytes()).await {
+        panic!("failed to write JSON-RPC line: {err}");
+    }
+}
+
+#[tokio::test]
+async fn connect_stdio_performs_initialize_handshake() {
+    let (client_stdin, server_reader) = tokio::io::duplex(4096);
+    let (mut server_writer, client_stdout) = tokio::io::duplex(4096);
+
+    let server = tokio::spawn(async move {
+        let mut lines = BufReader::new(server_reader).lines();
+
+        let initialize = read_jsonrpc_line(&mut lines).await;
+        let JSONRPCMessage::Request(request) = initialize else {
+            panic!("expected initialize request");
+        };
+        assert_eq!(request.method, INITIALIZE_METHOD);
+        assert_eq!(
+            request.params,
+            Some(serde_json::json!({ "clientName": "test-client" }))
+        );
+        write_jsonrpc_line(
+            &mut server_writer,
+            JSONRPCMessage::Response(JSONRPCResponse {
+                id: request.id,
+                result: serde_json::json!({ "protocolVersion": PROTOCOL_VERSION }),
+            }),
+        )
+        .await;
+
+        let initialized = read_jsonrpc_line(&mut lines).await;
+        let JSONRPCMessage::Notification(JSONRPCNotification { method, params }) = initialized
+        else {
+            panic!("expected initialized notification");
+        };
+        assert_eq!(method, INITIALIZED_METHOD);
+        assert_eq!(params, Some(serde_json::json!({})));
+    });
+
+    let client = ExecServerClient::connect_stdio(client_stdin, client_stdout, test_options()).await;
+    if let Err(err) = client {
+        panic!("failed to connect test client: {err}");
+    }
+
+    if let Err(err) = server.await {
+        panic!("server task failed: {err}");
+    }
+}
+
+#[tokio::test]
+async fn connect_in_process_starts_processes_without_jsonrpc_transport() {
+    let client = match ExecServerClient::connect_in_process(test_options()).await {
+        Ok(client) => client,
+        Err(err) => panic!("failed to connect in-process client: {err}"),
+    };
+
+    let process = match client
+        .start_process(ExecParams {
+            process_id: "proc-1".to_string(),
+            argv: vec!["printf".to_string(), "hello".to_string()],
+            cwd: std::env::current_dir().unwrap_or_else(|err| panic!("missing cwd: {err}")),
+            env: HashMap::new(),
+            tty: false,
+            arg0: None,
+            sandbox: None,
+        })
+        .await
+    {
+        Ok(process) => process,
+        Err(err) => panic!("failed to start in-process child: {err}"),
+    };
+
+    let mut output = process.output_receiver();
+    let output = timeout(Duration::from_secs(1), output.recv())
+        .await
+        .unwrap_or_else(|err| panic!("timed out waiting for process output: {err}"))
+        .unwrap_or_else(|err| panic!("failed to receive process output: {err}"));
+    assert_eq!(
+        output,
+        ExecServerOutput {
+            stream: crate::protocol::ExecOutputStream::Stdout,
+            chunk: b"hello".to_vec(),
+        }
+    );
+}
+
+#[tokio::test]
+async fn connect_in_process_read_returns_retained_output_and_exit_state() {
+    let client = match ExecServerClient::connect_in_process(test_options()).await {
+        Ok(client) => client,
+        Err(err) => panic!("failed to connect in-process client: {err}"),
+    };
+
+    let response = match client
+        .exec(ExecParams {
+            process_id: "proc-1".to_string(),
+            argv: vec!["printf".to_string(), "hello".to_string()],
+            cwd: std::env::current_dir().unwrap_or_else(|err| panic!("missing cwd: {err}")),
+            env: HashMap::new(),
+            tty: false,
+            arg0: None,
+            sandbox: None,
+        })
+        .await
+    {
+        Ok(response) => response,
+        Err(err) => panic!("failed to start in-process child: {err}"),
+    };
+
+    let process_id = response.process_id.clone();
+    let read = match client
+        .read(ReadParams {
+            process_id: process_id.clone(),
+            after_seq: None,
+            max_bytes: None,
+            wait_ms: Some(1000),
+        })
+        .await
+    {
+        Ok(read) => read,
+        Err(err) => panic!("failed to read in-process child output: {err}"),
+    };
+
+    assert_eq!(read.chunks.len(), 1);
+    assert_eq!(read.chunks[0].seq, 1);
+    assert_eq!(read.chunks[0].stream, ExecOutputStream::Stdout);
+    assert_eq!(read.chunks[0].chunk.clone().into_inner(), b"hello".to_vec());
+    assert_eq!(read.next_seq, 2);
+    let read = if read.exited {
+        read
+    } else {
+        match client
+            .read(ReadParams {
+                process_id,
+                after_seq: Some(read.next_seq - 1),
+                max_bytes: None,
+                wait_ms: Some(1000),
+            })
+            .await
+        {
+            Ok(read) => read,
+            Err(err) => panic!("failed to wait for in-process child exit: {err}"),
+        }
+    };
+    assert!(read.exited);
+    assert_eq!(read.exit_code, Some(0));
+}
+
+#[tokio::test]
+async fn connect_in_process_rejects_invalid_exec_params_from_handler() {
+    let client = match ExecServerClient::connect_in_process(test_options()).await {
+        Ok(client) => client,
+        Err(err) => panic!("failed to connect in-process client: {err}"),
+    };
+
+    let result = client
+        .start_process(ExecParams {
+            process_id: "proc-1".to_string(),
+            argv: Vec::new(),
+            cwd: std::env::current_dir().unwrap_or_else(|err| panic!("missing cwd: {err}")),
+            env: HashMap::new(),
+            tty: false,
+            arg0: None,
+            sandbox: None,
+        })
+        .await;
+
+    match result {
+        Err(ExecServerError::Server { code, message }) => {
+            assert_eq!(code, -32602);
+            assert_eq!(message, "argv must not be empty");
+        }
+        Err(err) => panic!("unexpected in-process exec failure: {err}"),
+        Ok(_) => panic!("expected invalid params error"),
+    }
+}
+
+#[tokio::test]
+async fn connect_in_process_rejects_writes_to_unknown_processes() {
+    let client = match ExecServerClient::connect_in_process(test_options()).await {
+        Ok(client) => client,
+        Err(err) => panic!("failed to connect in-process client: {err}"),
+    };
+
+    let result = client.write("missing", b"input".to_vec()).await;
+
+    match result {
+        Err(ExecServerError::Server { code, message }) => {
+            assert_eq!(code, -32600);
+            assert_eq!(message, "unknown process id missing");
+        }
+        Err(err) => panic!("unexpected in-process write failure: {err}"),
+        Ok(_) => panic!("expected unknown process error"),
+    }
+}
+
+#[tokio::test]
+async fn connect_in_process_terminate_marks_process_exited() {
+    let client = match ExecServerClient::connect_in_process(test_options()).await {
+        Ok(client) => client,
+        Err(err) => panic!("failed to connect in-process client: {err}"),
+    };
+
+    let process = match client
+        .start_process(ExecParams {
+            process_id: "proc-1".to_string(),
+            argv: vec!["sleep".to_string(), "30".to_string()],
+            cwd: std::env::current_dir().unwrap_or_else(|err| panic!("missing cwd: {err}")),
+            env: HashMap::new(),
+            tty: false,
+            arg0: None,
+            sandbox: None,
+        })
+        .await
+    {
+        Ok(process) => process,
+        Err(err) => panic!("failed to start in-process child: {err}"),
+    };
+
+    if let Err(err) = client.terminate(&process.process_id).await {
+        panic!("failed to terminate in-process child: {err}");
+    }
+
+    timeout(Duration::from_secs(2), async {
+        loop {
+            if process.has_exited() {
+                break;
+            }
+            tokio::time::sleep(Duration::from_millis(10)).await;
+        }
+    })
+    .await
+    .unwrap_or_else(|err| panic!("timed out waiting for in-process child to exit: {err}"));
+
+    assert!(process.has_exited());
+}
+
+#[tokio::test]
+async fn dropping_in_process_client_terminates_running_processes() {
+    let marker_path = std::env::temp_dir().join(format!(
+        "codex-exec-server-inprocess-drop-{}-{}",
+        std::process::id(),
+        std::time::SystemTime::now()
+            .duration_since(std::time::UNIX_EPOCH)
+            .expect("system time")
+            .as_nanos()
+    ));
+    let _ = std::fs::remove_file(&marker_path);
+
+    {
+        let client = match ExecServerClient::connect_in_process(test_options()).await {
+            Ok(client) => client,
+            Err(err) => panic!("failed to connect in-process client: {err}"),
+        };
+
+        let _ = client
+            .exec(ExecParams {
+                process_id: "proc-1".to_string(),
+                argv: vec![
+                    "/bin/sh".to_string(),
+                    "-c".to_string(),
+                    format!("sleep 2; printf dropped > {}", marker_path.display()),
+                ],
+                cwd: std::env::current_dir().expect("cwd"),
+                env: HashMap::new(),
+                tty: false,
+                arg0: None,
+                sandbox: None,
+            })
+            .await
+            .unwrap_or_else(|err| panic!("failed to start in-process child: {err}"));
+    }
+
+    tokio::time::sleep(Duration::from_secs(3)).await;
+    assert!(
+        !marker_path.exists(),
+        "dropping the in-process client should terminate managed children"
+    );
+    let _ = std::fs::remove_file(&marker_path);
+}
+
+#[tokio::test]
+async fn connect_stdio_returns_initialize_errors() {
+    let (client_stdin, server_reader) = tokio::io::duplex(4096);
+    let (mut server_writer, client_stdout) = tokio::io::duplex(4096);
+
+    tokio::spawn(async move {
+        let mut lines = BufReader::new(server_reader).lines();
+
+        let initialize = read_jsonrpc_line(&mut lines).await;
+        let JSONRPCMessage::Request(request) = initialize else {
+            panic!("expected initialize request");
+        };
+        write_jsonrpc_line(
+            &mut server_writer,
+            JSONRPCMessage::Error(JSONRPCError {
+                id: request.id,
+                error: JSONRPCErrorError {
+                    code: -32600,
+                    message: "rejected".to_string(),
+                    data: None,
+                },
+            }),
+        )
+        .await;
+    });
+
+    let result = ExecServerClient::connect_stdio(client_stdin, client_stdout, test_options()).await;
+
+    match result {
+        Err(ExecServerError::Server { code, message }) => {
+            assert_eq!(code, -32600);
+            assert_eq!(message, "rejected");
+        }
+        Err(err) => panic!("unexpected initialize failure: {err}"),
+        Ok(_) => panic!("expected initialize failure"),
+    }
+}
+
+#[tokio::test]
+async fn start_process_cleans_up_registered_process_after_request_error() {
+    let (client_stdin, server_reader) = tokio::io::duplex(4096);
+    let (mut server_writer, client_stdout) = tokio::io::duplex(4096);
+
+    tokio::spawn(async move {
+        let mut lines = BufReader::new(server_reader).lines();
+
+        let initialize = read_jsonrpc_line(&mut lines).await;
+        let JSONRPCMessage::Request(initialize_request) = initialize else {
+            panic!("expected initialize request");
+        };
+        write_jsonrpc_line(
+            &mut server_writer,
+            JSONRPCMessage::Response(JSONRPCResponse {
+                id: initialize_request.id,
+                result: serde_json::json!({ "protocolVersion": PROTOCOL_VERSION }),
+            }),
+        )
+        .await;
+
+        let initialized = read_jsonrpc_line(&mut lines).await;
+        let JSONRPCMessage::Notification(notification) = initialized else {
+            panic!("expected initialized notification");
+        };
+        assert_eq!(notification.method, INITIALIZED_METHOD);
+
+        let exec_request = read_jsonrpc_line(&mut lines).await;
+        let JSONRPCMessage::Request(JSONRPCRequest { id, method, .. }) = exec_request else {
+            panic!("expected exec request");
+        };
+        assert_eq!(method, EXEC_METHOD);
+        write_jsonrpc_line(
+            &mut server_writer,
+            JSONRPCMessage::Error(JSONRPCError {
+                id,
+                error: JSONRPCErrorError {
+                    code: -32600,
+                    message: "duplicate process".to_string(),
+                    data: None,
+                },
+            }),
+        )
+        .await;
+    });
+
+    let client =
+        match ExecServerClient::connect_stdio(client_stdin, client_stdout, test_options()).await {
+            Ok(client) => client,
+            Err(err) => panic!("failed to connect test client: {err}"),
+        };
+
+    let result = client
+        .start_process(ExecParams {
+            process_id: "proc-1".to_string(),
+            argv: vec!["bash".to_string(), "-lc".to_string(), "true".to_string()],
+            cwd: std::env::current_dir().unwrap_or_else(|err| panic!("missing cwd: {err}")),
+            env: HashMap::new(),
+            tty: true,
+            arg0: None,
+            sandbox: None,
+        })
+        .await;
+
+    match result {
+        Err(ExecServerError::Server { code, message }) => {
+            assert_eq!(code, -32600);
+            assert_eq!(message, "duplicate process");
+        }
+        Err(err) => panic!("unexpected start_process failure: {err}"),
+        Ok(_) => panic!("expected start_process failure"),
+    }
+
+    assert!(
+        client.inner.pending.lock().await.is_empty(),
+        "failed requests should not leave pending request state behind"
+    );
+}
+
+#[tokio::test]
+async fn connect_stdio_times_out_during_initialize_handshake() {
+    let (client_stdin, server_reader) = tokio::io::duplex(4096);
+    let (_server_writer, client_stdout) = tokio::io::duplex(4096);
+
+    tokio::spawn(async move {
+        let mut lines = BufReader::new(server_reader).lines();
+        let _ = read_jsonrpc_line(&mut lines).await;
+        tokio::time::sleep(Duration::from_millis(200)).await;
+    });
+
+    let result = ExecServerClient::connect_stdio(
+        client_stdin,
+        client_stdout,
+        ExecServerClientConnectOptions {
+            client_name: "test-client".to_string(),
+            initialize_timeout: Duration::from_millis(25),
+        },
+    )
+    .await;
+
+    match result {
+        Err(ExecServerError::InitializeTimedOut { timeout }) => {
+            assert_eq!(timeout, Duration::from_millis(25));
+        }
+        Err(err) => panic!("unexpected initialize timeout failure: {err}"),
+        Ok(_) => panic!("expected initialize timeout"),
+    }
+}
+
+#[tokio::test]
+async fn start_process_preserves_output_stream_metadata() {
+    let (client_stdin, server_reader) = tokio::io::duplex(4096);
+    let (mut server_writer, client_stdout) = tokio::io::duplex(4096);
+
+    tokio::spawn(async move {
+        let mut lines = BufReader::new(server_reader).lines();
+
+        let initialize = read_jsonrpc_line(&mut lines).await;
+        let JSONRPCMessage::Request(initialize_request) = initialize else {
+            panic!("expected initialize request");
+        };
+        write_jsonrpc_line(
+            &mut server_writer,
+            JSONRPCMessage::Response(JSONRPCResponse {
+                id: initialize_request.id,
+                result: serde_json::json!({ "protocolVersion": PROTOCOL_VERSION }),
+            }),
+        )
+        .await;
+
+        let initialized = read_jsonrpc_line(&mut lines).await;
+        let JSONRPCMessage::Notification(notification) = initialized else {
+            panic!("expected initialized notification");
+        };
+        assert_eq!(notification.method, INITIALIZED_METHOD);
+
+        let exec_request = read_jsonrpc_line(&mut lines).await;
+        let JSONRPCMessage::Request(JSONRPCRequest { id, method, .. }) = exec_request else {
+            panic!("expected exec request");
+        };
+        assert_eq!(method, EXEC_METHOD);
+        write_jsonrpc_line(
+            &mut server_writer,
+            JSONRPCMessage::Response(JSONRPCResponse {
+                id,
+                result: serde_json::json!({ "processId": "proc-1" }),
+            }),
+        )
+        .await;
+        tokio::time::sleep(Duration::from_millis(25)).await;
+        write_jsonrpc_line(
+            &mut server_writer,
+            JSONRPCMessage::Notification(JSONRPCNotification {
+                method: EXEC_OUTPUT_DELTA_METHOD.to_string(),
+                params: Some(serde_json::json!({
+                    "processId": "proc-1",
+                    "stream": "stderr",
+                    "chunk": "ZXJyb3IK"
+                })),
+            }),
+        )
+        .await;
+        tokio::time::sleep(Duration::from_millis(100)).await;
+    });
+
+    let client =
+        match ExecServerClient::connect_stdio(client_stdin, client_stdout, test_options()).await {
+            Ok(client) => client,
+            Err(err) => panic!("failed to connect test client: {err}"),
+        };
+
+    let process = match client
+        .start_process(ExecParams {
+            process_id: "proc-1".to_string(),
+            argv: vec!["bash".to_string(), "-lc".to_string(), "true".to_string()],
+            cwd: std::env::current_dir().unwrap_or_else(|err| panic!("missing cwd: {err}")),
+            env: HashMap::new(),
+            tty: true,
+            arg0: None,
+            sandbox: None,
+        })
+        .await
+    {
+        Ok(process) => process,
+        Err(err) => panic!("failed to start process: {err}"),
+    };
+
+    let mut output = process.output_receiver();
+    let output = timeout(Duration::from_secs(1), output.recv())
+        .await
+        .unwrap_or_else(|err| panic!("timed out waiting for process output: {err}"))
+        .unwrap_or_else(|err| panic!("failed to receive process output: {err}"));
+    assert_eq!(output.stream, ExecOutputStream::Stderr);
+    assert_eq!(output.chunk, b"error\n".to_vec());
+}
+
+#[tokio::test]
+async fn terminate_does_not_mark_process_exited_before_exit_notification() {
+    let (client_stdin, server_reader) = tokio::io::duplex(4096);
+    let (mut server_writer, client_stdout) = tokio::io::duplex(4096);
+
+    tokio::spawn(async move {
+        let mut lines = BufReader::new(server_reader).lines();
+
+        let initialize = read_jsonrpc_line(&mut lines).await;
+        let JSONRPCMessage::Request(initialize_request) = initialize else {
+            panic!("expected initialize request");
+        };
+        write_jsonrpc_line(
+            &mut server_writer,
+            JSONRPCMessage::Response(JSONRPCResponse {
+                id: initialize_request.id,
+                result: serde_json::json!({ "protocolVersion": PROTOCOL_VERSION }),
+            }),
+        )
+        .await;
+
+        let initialized = read_jsonrpc_line(&mut lines).await;
+        let JSONRPCMessage::Notification(notification) = initialized else {
+            panic!("expected initialized notification");
+        };
+        assert_eq!(notification.method, INITIALIZED_METHOD);
+
+        let exec_request = read_jsonrpc_line(&mut lines).await;
+        let JSONRPCMessage::Request(JSONRPCRequest { id, method, .. }) = exec_request else {
+            panic!("expected exec request");
+        };
+        assert_eq!(method, EXEC_METHOD);
+        write_jsonrpc_line(
+            &mut server_writer,
+            JSONRPCMessage::Response(JSONRPCResponse {
+                id,
+                result: serde_json::json!({ "processId": "proc-1" }),
+            }),
+        )
+        .await;
+
+        let terminate_request = read_jsonrpc_line(&mut lines).await;
+        let JSONRPCMessage::Request(JSONRPCRequest { id, method, .. }) = terminate_request else {
+            panic!("expected terminate request");
+        };
+        assert_eq!(method, EXEC_TERMINATE_METHOD);
+        write_jsonrpc_line(
+            &mut server_writer,
+            JSONRPCMessage::Response(JSONRPCResponse {
+                id,
+                result: serde_json::json!({ "running": true }),
+            }),
+        )
+        .await;
+        tokio::time::sleep(Duration::from_millis(100)).await;
+    });
+
+    let client =
+        match ExecServerClient::connect_stdio(client_stdin, client_stdout, test_options()).await {
+            Ok(client) => client,
+            Err(err) => panic!("failed to connect test client: {err}"),
+        };
+
+    let process = match client
+        .start_process(ExecParams {
+            process_id: "proc-1".to_string(),
+            argv: vec!["bash".to_string(), "-lc".to_string(), "true".to_string()],
+            cwd: std::env::current_dir().unwrap_or_else(|err| panic!("missing cwd: {err}")),
+            env: HashMap::new(),
+            tty: true,
+            arg0: None,
+            sandbox: None,
+        })
+        .await
+    {
+        Ok(process) => process,
+        Err(err) => panic!("failed to start process: {err}"),
+    };
+
+    process.terminate();
+    tokio::time::sleep(Duration::from_millis(25)).await;
+    assert!(!process.has_exited(), "terminate should not imply exit");
+    assert_eq!(process.exit_code(), None);
+}
+
+#[tokio::test]
+async fn start_process_uses_protocol_process_ids() {
+    let (client_stdin, server_reader) = tokio::io::duplex(4096);
+    let (mut server_writer, client_stdout) = tokio::io::duplex(4096);
+
+    tokio::spawn(async move {
+        let mut lines = BufReader::new(server_reader).lines();
+
+        let initialize = read_jsonrpc_line(&mut lines).await;
+        let JSONRPCMessage::Request(initialize_request) = initialize else {
+            panic!("expected initialize request");
+        };
+        write_jsonrpc_line(
+            &mut server_writer,
+            JSONRPCMessage::Response(JSONRPCResponse {
+                id: initialize_request.id,
+                result: serde_json::json!({ "protocolVersion": PROTOCOL_VERSION }),
+            }),
+        )
+        .await;
+
+        let initialized = read_jsonrpc_line(&mut lines).await;
+        let JSONRPCMessage::Notification(notification) = initialized else {
+            panic!("expected initialized notification");
+        };
+        assert_eq!(notification.method, INITIALIZED_METHOD);
+
+        let exec_request = read_jsonrpc_line(&mut lines).await;
+        let JSONRPCMessage::Request(JSONRPCRequest { id, method, .. }) = exec_request else {
+            panic!("expected exec request");
+        };
+        assert_eq!(method, EXEC_METHOD);
+        write_jsonrpc_line(
+            &mut server_writer,
+            JSONRPCMessage::Response(JSONRPCResponse {
+                id,
+                result: serde_json::json!({ "processId": "other-proc" }),
+            }),
+        )
+        .await;
+    });
+
+    let client =
+        match ExecServerClient::connect_stdio(client_stdin, client_stdout, test_options()).await {
+            Ok(client) => client,
+            Err(err) => panic!("failed to connect test client: {err}"),
+        };
+
+    let process = match client
+        .start_process(ExecParams {
+            process_id: "proc-1".to_string(),
+            argv: vec!["bash".to_string(), "-lc".to_string(), "true".to_string()],
+            cwd: std::env::current_dir().unwrap_or_else(|err| panic!("missing cwd: {err}")),
+            env: HashMap::new(),
+            tty: true,
+            arg0: None,
+            sandbox: None,
+        })
+        .await
+    {
+        Ok(process) => process,
+        Err(err) => panic!("failed to start process: {err}"),
+    };
+
+    assert_eq!(process.process_id, "other-proc");
+}
+
+#[tokio::test]
+async fn start_process_routes_output_for_protocol_process_ids() {
+    let (client_stdin, server_reader) = tokio::io::duplex(4096);
+    let (mut server_writer, client_stdout) = tokio::io::duplex(4096);
+
+    tokio::spawn(async move {
+        let mut lines = BufReader::new(server_reader).lines();
+
+        let initialize = read_jsonrpc_line(&mut lines).await;
+        let JSONRPCMessage::Request(initialize_request) = initialize else {
+            panic!("expected initialize request");
+        };
+        write_jsonrpc_line(
+            &mut server_writer,
+            JSONRPCMessage::Response(JSONRPCResponse {
+                id: initialize_request.id,
+                result: serde_json::json!({ "protocolVersion": PROTOCOL_VERSION }),
+            }),
+        )
+        .await;
+
+        let initialized = read_jsonrpc_line(&mut lines).await;
+        let JSONRPCMessage::Notification(notification) = initialized else {
+            panic!("expected initialized notification");
+        };
+        assert_eq!(notification.method, INITIALIZED_METHOD);
+
+        let exec_request = read_jsonrpc_line(&mut lines).await;
+        let JSONRPCMessage::Request(JSONRPCRequest { id, method, .. }) = exec_request else {
+            panic!("expected exec request");
+        };
+        assert_eq!(method, EXEC_METHOD);
+        write_jsonrpc_line(
+            &mut server_writer,
+            JSONRPCMessage::Response(JSONRPCResponse {
+                id,
+                result: serde_json::json!({ "processId": "proc-1" }),
+            }),
+        )
+        .await;
+        tokio::time::sleep(Duration::from_millis(25)).await;
+        write_jsonrpc_line(
+            &mut server_writer,
+            JSONRPCMessage::Notification(JSONRPCNotification {
+                method: EXEC_OUTPUT_DELTA_METHOD.to_string(),
+                params: Some(serde_json::json!({
+                    "processId": "proc-1",
+                    "stream": "stdout",
+                    "chunk": "YWxpdmUK"
+                })),
+            }),
+        )
+        .await;
+    });
+
+    let client =
+        match ExecServerClient::connect_stdio(client_stdin, client_stdout, test_options()).await {
+            Ok(client) => client,
+            Err(err) => panic!("failed to connect test client: {err}"),
+        };
+
+    let first_process = match client
+        .start_process(ExecParams {
+            process_id: "proc-1".to_string(),
+            argv: vec!["bash".to_string(), "-lc".to_string(), "true".to_string()],
+            cwd: std::env::current_dir().unwrap_or_else(|err| panic!("missing cwd: {err}")),
+            env: HashMap::new(),
+            tty: true,
+            arg0: None,
+            sandbox: None,
+        })
+        .await
+    {
+        Ok(process) => process,
+        Err(err) => panic!("failed to start first process: {err}"),
+    };
+
+    let mut output = first_process.output_receiver();
+    let output = timeout(Duration::from_secs(1), output.recv())
+        .await
+        .unwrap_or_else(|err| panic!("timed out waiting for process output: {err}"))
+        .unwrap_or_else(|err| panic!("failed to receive process output: {err}"));
+    assert_eq!(output.stream, ExecOutputStream::Stdout);
+    assert_eq!(output.chunk, b"alive\n".to_vec());
+}
+
+#[tokio::test]
+async fn transport_shutdown_marks_processes_exited_without_exit_codes() {
+    let (client_stdin, server_reader) = tokio::io::duplex(4096);
+    let (mut server_writer, client_stdout) = tokio::io::duplex(4096);
+
+    tokio::spawn(async move {
+        let mut lines = BufReader::new(server_reader).lines();
+
+        let initialize = read_jsonrpc_line(&mut lines).await;
+        let JSONRPCMessage::Request(initialize_request) = initialize else {
+            panic!("expected initialize request");
+        };
+        write_jsonrpc_line(
+            &mut server_writer,
+            JSONRPCMessage::Response(JSONRPCResponse {
+                id: initialize_request.id,
+                result: serde_json::json!({ "protocolVersion": PROTOCOL_VERSION }),
+            }),
+        )
+        .await;
+
+        let initialized = read_jsonrpc_line(&mut lines).await;
+        let JSONRPCMessage::Notification(notification) = initialized else {
+            panic!("expected initialized notification");
+        };
+        assert_eq!(notification.method, INITIALIZED_METHOD);
+
+        let exec_request = read_jsonrpc_line(&mut lines).await;
+        let JSONRPCMessage::Request(JSONRPCRequest { id, method, .. }) = exec_request else {
+            panic!("expected exec request");
+        };
+        assert_eq!(method, EXEC_METHOD);
+        write_jsonrpc_line(
+            &mut server_writer,
+            JSONRPCMessage::Response(JSONRPCResponse {
+                id,
+                result: serde_json::json!({ "processId": "proc-1" }),
+            }),
+        )
+        .await;
+        drop(server_writer);
+    });
+
+    let client =
+        match ExecServerClient::connect_stdio(client_stdin, client_stdout, test_options()).await {
+            Ok(client) => client,
+            Err(err) => panic!("failed to connect test client: {err}"),
+        };
+
+    let process = match client
+        .start_process(ExecParams {
+            process_id: "proc-1".to_string(),
+            argv: vec!["bash".to_string(), "-lc".to_string(), "true".to_string()],
+            cwd: std::env::current_dir().unwrap_or_else(|err| panic!("missing cwd: {err}")),
+            env: HashMap::new(),
+            tty: true,
+            arg0: None,
+            sandbox: None,
+        })
+        .await
+    {
+        Ok(process) => process,
+        Err(err) => panic!("failed to start process: {err}"),
+    };
+
+    let _ = process;
+}

codex-rs/exec-server/src/client_api.rs

@@ -0,0 +1,27 @@
+use std::time::Duration;
+
+use crate::protocol::ExecExitedNotification;
+use crate::protocol::ExecOutputDeltaNotification;
+
+/// Connection options for any exec-server client transport.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct ExecServerClientConnectOptions {
+    pub client_name: String,
+    pub initialize_timeout: Duration,
+}
+
+/// WebSocket connection arguments for a remote exec-server.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct RemoteExecServerConnectArgs {
+    pub websocket_url: String,
+    pub client_name: String,
+    pub connect_timeout: Duration,
+    pub initialize_timeout: Duration,
+}
+
+/// Connection-level server events.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum ExecServerEvent {
+    OutputDelta(ExecOutputDeltaNotification),
+    Exited(ExecExitedNotification),
+}

codex-rs/exec-server/src/connection.rs

@@ -0,0 +1,421 @@
+use codex_app_server_protocol::JSONRPCMessage;
+use futures::SinkExt;
+use futures::StreamExt;
+use tokio::io::AsyncBufReadExt;
+use tokio::io::AsyncRead;
+use tokio::io::AsyncWrite;
+use tokio::io::AsyncWriteExt;
+use tokio::io::BufReader;
+use tokio::io::BufWriter;
+use tokio::sync::mpsc;
+use tokio_tungstenite::WebSocketStream;
+use tokio_tungstenite::tungstenite::Message;
+
+pub(crate) const CHANNEL_CAPACITY: usize = 128;
+
+#[derive(Debug)]
+pub(crate) enum JsonRpcConnectionEvent {
+    Message(JSONRPCMessage),
+    Disconnected { reason: Option<String> },
+}
+
+pub(crate) struct JsonRpcConnection {
+    outgoing_tx: mpsc::Sender<JSONRPCMessage>,
+    incoming_rx: mpsc::Receiver<JsonRpcConnectionEvent>,
+    task_handles: Vec<tokio::task::JoinHandle<()>>,
+}
+
+impl JsonRpcConnection {
+    pub(crate) fn from_stdio<R, W>(reader: R, writer: W, connection_label: String) -> Self
+    where
+        R: AsyncRead + Unpin + Send + 'static,
+        W: AsyncWrite + Unpin + Send + 'static,
+    {
+        let (outgoing_tx, mut outgoing_rx) = mpsc::channel(CHANNEL_CAPACITY);
+        let (incoming_tx, incoming_rx) = mpsc::channel(CHANNEL_CAPACITY);
+
+        let reader_label = connection_label.clone();
+        let incoming_tx_for_reader = incoming_tx.clone();
+        let reader_task = tokio::spawn(async move {
+            let mut lines = BufReader::new(reader).lines();
+            loop {
+                match lines.next_line().await {
+                    Ok(Some(line)) => {
+                        if line.trim().is_empty() {
+                            continue;
+                        }
+                        match serde_json::from_str::<JSONRPCMessage>(&line) {
+                            Ok(message) => {
+                                if incoming_tx_for_reader
+                                    .send(JsonRpcConnectionEvent::Message(message))
+                                    .await
+                                    .is_err()
+                                {
+                                    break;
+                                }
+                            }
+                            Err(err) => {
+                                send_disconnected(
+                                    &incoming_tx_for_reader,
+                                    Some(format!(
+                                        "failed to parse JSON-RPC message from {reader_label}: {err}"
+                                    )),
+                                )
+                                .await;
+                                break;
+                            }
+                        }
+                    }
+                    Ok(None) => {
+                        send_disconnected(&incoming_tx_for_reader, /*reason*/ None).await;
+                        break;
+                    }
+                    Err(err) => {
+                        send_disconnected(
+                            &incoming_tx_for_reader,
+                            Some(format!(
+                                "failed to read JSON-RPC message from {reader_label}: {err}"
+                            )),
+                        )
+                        .await;
+                        break;
+                    }
+                }
+            }
+        });
+
+        let writer_task = tokio::spawn(async move {
+            let mut writer = BufWriter::new(writer);
+            while let Some(message) = outgoing_rx.recv().await {
+                if let Err(err) = write_jsonrpc_line_message(&mut writer, &message).await {
+                    send_disconnected(
+                        &incoming_tx,
+                        Some(format!(
+                            "failed to write JSON-RPC message to {connection_label}: {err}"
+                        )),
+                    )
+                    .await;
+                    break;
+                }
+            }
+        });
+
+        Self {
+            outgoing_tx,
+            incoming_rx,
+            task_handles: vec![reader_task, writer_task],
+        }
+    }
+
+    pub(crate) fn from_websocket<S>(stream: WebSocketStream<S>, connection_label: String) -> Self
+    where
+        S: AsyncRead + AsyncWrite + Unpin + Send + 'static,
+    {
+        let (outgoing_tx, mut outgoing_rx) = mpsc::channel(CHANNEL_CAPACITY);
+        let (incoming_tx, incoming_rx) = mpsc::channel(CHANNEL_CAPACITY);
+        let (mut websocket_writer, mut websocket_reader) = stream.split();
+
+        let reader_label = connection_label.clone();
+        let incoming_tx_for_reader = incoming_tx.clone();
+        let reader_task = tokio::spawn(async move {
+            loop {
+                match websocket_reader.next().await {
+                    Some(Ok(Message::Text(text))) => {
+                        match serde_json::from_str::<JSONRPCMessage>(text.as_ref()) {
+                            Ok(message) => {
+                                if incoming_tx_for_reader
+                                    .send(JsonRpcConnectionEvent::Message(message))
+                                    .await
+                                    .is_err()
+                                {
+                                    break;
+                                }
+                            }
+                            Err(err) => {
+                                send_disconnected(
+                                    &incoming_tx_for_reader,
+                                    Some(format!(
+                                        "failed to parse websocket JSON-RPC message from {reader_label}: {err}"
+                                    )),
+                                )
+                                .await;
+                                break;
+                            }
+                        }
+                    }
+                    Some(Ok(Message::Binary(bytes))) => {
+                        match serde_json::from_slice::<JSONRPCMessage>(bytes.as_ref()) {
+                            Ok(message) => {
+                                if incoming_tx_for_reader
+                                    .send(JsonRpcConnectionEvent::Message(message))
+                                    .await
+                                    .is_err()
+                                {
+                                    break;
+                                }
+                            }
+                            Err(err) => {
+                                send_disconnected(
+                                    &incoming_tx_for_reader,
+                                    Some(format!(
+                                        "failed to parse websocket JSON-RPC message from {reader_label}: {err}"
+                                    )),
+                                )
+                                .await;
+                                break;
+                            }
+                        }
+                    }
+                    Some(Ok(Message::Close(_))) => {
+                        send_disconnected(&incoming_tx_for_reader, /*reason*/ None).await;
+                        break;
+                    }
+                    Some(Ok(Message::Ping(_))) | Some(Ok(Message::Pong(_))) => {}
+                    Some(Ok(_)) => {}
+                    Some(Err(err)) => {
+                        send_disconnected(
+                            &incoming_tx_for_reader,
+                            Some(format!(
+                                "failed to read websocket JSON-RPC message from {reader_label}: {err}"
+                            )),
+                        )
+                        .await;
+                        break;
+                    }
+                    None => {
+                        send_disconnected(&incoming_tx_for_reader, /*reason*/ None).await;
+                        break;
+                    }
+                }
+            }
+        });
+
+        let writer_task = tokio::spawn(async move {
+            while let Some(message) = outgoing_rx.recv().await {
+                match serialize_jsonrpc_message(&message) {
+                    Ok(encoded) => {
+                        if let Err(err) = websocket_writer.send(Message::Text(encoded.into())).await
+                        {
+                            send_disconnected(
+                                &incoming_tx,
+                                Some(format!(
+                                    "failed to write websocket JSON-RPC message to {connection_label}: {err}"
+                                )),
+                            )
+                            .await;
+                            break;
+                        }
+                    }
+                    Err(err) => {
+                        send_disconnected(
+                            &incoming_tx,
+                            Some(format!(
+                                "failed to serialize JSON-RPC message for {connection_label}: {err}"
+                            )),
+                        )
+                        .await;
+                        break;
+                    }
+                }
+            }
+        });
+
+        Self {
+            outgoing_tx,
+            incoming_rx,
+            task_handles: vec![reader_task, writer_task],
+        }
+    }
+
+    pub(crate) fn into_parts(
+        self,
+    ) -> (
+        mpsc::Sender<JSONRPCMessage>,
+        mpsc::Receiver<JsonRpcConnectionEvent>,
+        Vec<tokio::task::JoinHandle<()>>,
+    ) {
+        (self.outgoing_tx, self.incoming_rx, self.task_handles)
+    }
+}
+
+async fn send_disconnected(
+    incoming_tx: &mpsc::Sender<JsonRpcConnectionEvent>,
+    reason: Option<String>,
+) {
+    let _ = incoming_tx
+        .send(JsonRpcConnectionEvent::Disconnected { reason })
+        .await;
+}
+
+async fn write_jsonrpc_line_message<W>(
+    writer: &mut BufWriter<W>,
+    message: &JSONRPCMessage,
+) -> std::io::Result<()>
+where
+    W: AsyncWrite + Unpin,
+{
+    let encoded =
+        serialize_jsonrpc_message(message).map_err(|err| std::io::Error::other(err.to_string()))?;
+    writer.write_all(encoded.as_bytes()).await?;
+    writer.write_all(b"\n").await?;
+    writer.flush().await
+}
+
+fn serialize_jsonrpc_message(message: &JSONRPCMessage) -> Result<String, serde_json::Error> {
+    serde_json::to_string(message)
+}
+
+#[cfg(test)]
+mod tests {
+    use std::time::Duration;
+
+    use codex_app_server_protocol::JSONRPCMessage;
+    use codex_app_server_protocol::JSONRPCRequest;
+    use codex_app_server_protocol::JSONRPCResponse;
+    use codex_app_server_protocol::RequestId;
+    use pretty_assertions::assert_eq;
+    use tokio::io::AsyncBufReadExt;
+    use tokio::io::AsyncWriteExt;
+    use tokio::io::BufReader;
+    use tokio::sync::mpsc;
+    use tokio::time::timeout;
+
+    use super::JsonRpcConnection;
+    use super::JsonRpcConnectionEvent;
+    use super::serialize_jsonrpc_message;
+
+    async fn recv_event(
+        incoming_rx: &mut mpsc::Receiver<JsonRpcConnectionEvent>,
+    ) -> JsonRpcConnectionEvent {
+        let recv_result = timeout(Duration::from_secs(1), incoming_rx.recv()).await;
+        let maybe_event = match recv_result {
+            Ok(maybe_event) => maybe_event,
+            Err(err) => panic!("timed out waiting for connection event: {err}"),
+        };
+        match maybe_event {
+            Some(event) => event,
+            None => panic!("connection event stream ended unexpectedly"),
+        }
+    }
+
+    async fn read_jsonrpc_line<R>(lines: &mut tokio::io::Lines<BufReader<R>>) -> JSONRPCMessage
+    where
+        R: tokio::io::AsyncRead + Unpin,
+    {
+        let next_line = timeout(Duration::from_secs(1), lines.next_line()).await;
+        let line_result = match next_line {
+            Ok(line_result) => line_result,
+            Err(err) => panic!("timed out waiting for JSON-RPC line: {err}"),
+        };
+        let maybe_line = match line_result {
+            Ok(maybe_line) => maybe_line,
+            Err(err) => panic!("failed to read JSON-RPC line: {err}"),
+        };
+        let line = match maybe_line {
+            Some(line) => line,
+            None => panic!("connection closed before JSON-RPC line arrived"),
+        };
+        match serde_json::from_str::<JSONRPCMessage>(&line) {
+            Ok(message) => message,
+            Err(err) => panic!("failed to parse JSON-RPC line: {err}"),
+        }
+    }
+
+    #[tokio::test]
+    async fn stdio_connection_reads_and_writes_jsonrpc_messages() {
+        let (mut writer_to_connection, connection_reader) = tokio::io::duplex(1024);
+        let (connection_writer, reader_from_connection) = tokio::io::duplex(1024);
+        let connection =
+            JsonRpcConnection::from_stdio(connection_reader, connection_writer, "test".to_string());
+        let (outgoing_tx, mut incoming_rx, _task_handles) = connection.into_parts();
+
+        let incoming_message = JSONRPCMessage::Request(JSONRPCRequest {
+            id: RequestId::Integer(7),
+            method: "initialize".to_string(),
+            params: Some(serde_json::json!({ "clientName": "test-client" })),
+            trace: None,
+        });
+        let encoded = match serialize_jsonrpc_message(&incoming_message) {
+            Ok(encoded) => encoded,
+            Err(err) => panic!("failed to serialize incoming message: {err}"),
+        };
+        if let Err(err) = writer_to_connection
+            .write_all(format!("{encoded}\n").as_bytes())
+            .await
+        {
+            panic!("failed to write to connection: {err}");
+        }
+
+        let event = recv_event(&mut incoming_rx).await;
+        match event {
+            JsonRpcConnectionEvent::Message(message) => {
+                assert_eq!(message, incoming_message);
+            }
+            JsonRpcConnectionEvent::Disconnected { reason } => {
+                panic!("unexpected disconnect event: {reason:?}");
+            }
+        }
+
+        let outgoing_message = JSONRPCMessage::Response(JSONRPCResponse {
+            id: RequestId::Integer(7),
+            result: serde_json::json!({ "protocolVersion": "exec-server.v0" }),
+        });
+        if let Err(err) = outgoing_tx.send(outgoing_message.clone()).await {
+            panic!("failed to queue outgoing message: {err}");
+        }
+
+        let mut lines = BufReader::new(reader_from_connection).lines();
+        let message = read_jsonrpc_line(&mut lines).await;
+        assert_eq!(message, outgoing_message);
+    }
+
+    #[tokio::test]
+    async fn stdio_connection_reports_parse_errors() {
+        let (mut writer_to_connection, connection_reader) = tokio::io::duplex(1024);
+        let (connection_writer, _reader_from_connection) = tokio::io::duplex(1024);
+        let connection =
+            JsonRpcConnection::from_stdio(connection_reader, connection_writer, "test".to_string());
+        let (_outgoing_tx, mut incoming_rx, _task_handles) = connection.into_parts();
+
+        if let Err(err) = writer_to_connection.write_all(b"not-json\n").await {
+            panic!("failed to write invalid JSON: {err}");
+        }
+
+        let event = recv_event(&mut incoming_rx).await;
+        match event {
+            JsonRpcConnectionEvent::Disconnected { reason } => {
+                let reason = match reason {
+                    Some(reason) => reason,
+                    None => panic!("expected a parse error reason"),
+                };
+                assert!(
+                    reason.contains("failed to parse JSON-RPC message from test"),
+                    "unexpected disconnect reason: {reason}"
+                );
+            }
+            JsonRpcConnectionEvent::Message(message) => {
+                panic!("unexpected JSON-RPC message: {message:?}");
+            }
+        }
+    }
+
+    #[tokio::test]
+    async fn stdio_connection_reports_clean_disconnect() {
+        let (writer_to_connection, connection_reader) = tokio::io::duplex(1024);
+        let (connection_writer, _reader_from_connection) = tokio::io::duplex(1024);
+        let connection =
+            JsonRpcConnection::from_stdio(connection_reader, connection_writer, "test".to_string());
+        let (_outgoing_tx, mut incoming_rx, _task_handles) = connection.into_parts();
+        drop(writer_to_connection);
+
+        let event = recv_event(&mut incoming_rx).await;
+        match event {
+            JsonRpcConnectionEvent::Disconnected { reason } => {
+                assert_eq!(reason, None);
+            }
+            JsonRpcConnectionEvent::Message(message) => {
+                panic!("unexpected JSON-RPC message: {message:?}");
+            }
+        }
+    }
+}

codex-rs/exec-server/src/lib.rs

@@ -0,0 +1,30 @@
+mod client;
+mod client_api;
+mod connection;
+mod local;
+mod protocol;
+mod server;
+
+pub use client::ExecServerClient;
+pub use client::ExecServerError;
+pub use client_api::ExecServerClientConnectOptions;
+pub use client_api::ExecServerEvent;
+pub use client_api::RemoteExecServerConnectArgs;
+pub use local::ExecServerLaunchCommand;
+pub use local::SpawnedExecServer;
+pub use local::spawn_local_exec_server;
+pub use protocol::ExecExitedNotification;
+pub use protocol::ExecOutputDeltaNotification;
+pub use protocol::ExecOutputStream;
+pub use protocol::ExecParams;
+pub use protocol::ExecResponse;
+pub use protocol::InitializeParams;
+pub use protocol::InitializeResponse;
+pub use protocol::TerminateParams;
+pub use protocol::TerminateResponse;
+pub use protocol::WriteParams;
+pub use protocol::WriteResponse;
+pub use server::ExecServerTransport;
+pub use server::ExecServerTransportParseError;
+pub use server::run_main;
+pub use server::run_main_with_transport;

codex-rs/exec-server/src/local.rs

@@ -0,0 +1,70 @@
+use std::path::PathBuf;
+use std::process::Stdio;
+use std::sync::Mutex as StdMutex;
+
+use tokio::process::Child;
+use tokio::process::Command;
+
+use crate::client::ExecServerClient;
+use crate::client::ExecServerError;
+use crate::client_api::ExecServerClientConnectOptions;
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct ExecServerLaunchCommand {
+    pub program: PathBuf,
+    pub args: Vec<String>,
+}
+
+pub struct SpawnedExecServer {
+    client: ExecServerClient,
+    child: StdMutex<Option<Child>>,
+}
+
+impl SpawnedExecServer {
+    pub fn client(&self) -> &ExecServerClient {
+        &self.client
+    }
+}
+
+impl Drop for SpawnedExecServer {
+    fn drop(&mut self) {
+        if let Ok(mut child_guard) = self.child.lock()
+            && let Some(child) = child_guard.as_mut()
+        {
+            let _ = child.start_kill();
+        }
+    }
+}
+
+pub async fn spawn_local_exec_server(
+    command: ExecServerLaunchCommand,
+    options: ExecServerClientConnectOptions,
+) -> Result<SpawnedExecServer, ExecServerError> {
+    let mut child = Command::new(&command.program);
+    child.args(&command.args);
+    child.stdin(Stdio::piped());
+    child.stdout(Stdio::piped());
+    child.stderr(Stdio::inherit());
+    child.kill_on_drop(true);
+
+    let mut child = child.spawn().map_err(ExecServerError::Spawn)?;
+    let stdin = child.stdin.take().ok_or_else(|| {
+        ExecServerError::Protocol("exec-server stdin was not captured".to_string())
+    })?;
+    let stdout = child.stdout.take().ok_or_else(|| {
+        ExecServerError::Protocol("exec-server stdout was not captured".to_string())
+    })?;
+
+    let client = match ExecServerClient::connect_stdio(stdin, stdout, options).await {
+        Ok(client) => client,
+        Err(err) => {
+            let _ = child.start_kill();
+            return Err(err);
+        }
+    };
+
+    Ok(SpawnedExecServer {
+        client,
+        child: StdMutex::new(Some(child)),
+    })
+}

codex-rs/exec-server/src/protocol.rs

@@ -0,0 +1,184 @@
+use std::collections::HashMap;
+use std::path::PathBuf;
+
+use base64::engine::general_purpose::STANDARD as BASE64_STANDARD;
+use serde::Deserialize;
+use serde::Serialize;
+
+pub const INITIALIZE_METHOD: &str = "initialize";
+pub const INITIALIZED_METHOD: &str = "initialized";
+pub const EXEC_METHOD: &str = "process/start";
+pub const EXEC_READ_METHOD: &str = "process/read";
+pub const EXEC_WRITE_METHOD: &str = "process/write";
+pub const EXEC_TERMINATE_METHOD: &str = "process/terminate";
+pub const EXEC_OUTPUT_DELTA_METHOD: &str = "process/output";
+pub const EXEC_EXITED_METHOD: &str = "process/exited";
+pub const FS_READ_FILE_METHOD: &str = "fs/readFile";
+pub const FS_WRITE_FILE_METHOD: &str = "fs/writeFile";
+pub const FS_CREATE_DIRECTORY_METHOD: &str = "fs/createDirectory";
+pub const FS_GET_METADATA_METHOD: &str = "fs/getMetadata";
+pub const FS_READ_DIRECTORY_METHOD: &str = "fs/readDirectory";
+pub const FS_REMOVE_METHOD: &str = "fs/remove";
+pub const FS_COPY_METHOD: &str = "fs/copy";
+pub const PROTOCOL_VERSION: &str = "exec-server.v0";
+
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(transparent)]
+pub struct ByteChunk(#[serde(with = "base64_bytes")] pub Vec<u8>);
+
+impl ByteChunk {
+    pub fn into_inner(self) -> Vec<u8> {
+        self.0
+    }
+}
+
+impl From<Vec<u8>> for ByteChunk {
+    fn from(value: Vec<u8>) -> Self {
+        Self(value)
+    }
+}
+
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct InitializeParams {
+    pub client_name: String,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct InitializeResponse {
+    pub protocol_version: String,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct ExecParams {
+    /// Client-chosen logical process handle scoped to this connection/session.
+    /// This is a protocol key, not an OS pid.
+    pub process_id: String,
+    pub argv: Vec<String>,
+    pub cwd: PathBuf,
+    pub env: HashMap<String, String>,
+    pub tty: bool,
+    pub arg0: Option<String>,
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub sandbox: Option<ExecSandboxConfig>,
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct ExecSandboxConfig {
+    pub mode: ExecSandboxMode,
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub enum ExecSandboxMode {
+    None,
+    HostDefault,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct ExecResponse {
+    pub process_id: String,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct ReadParams {
+    pub process_id: String,
+    pub after_seq: Option<u64>,
+    pub max_bytes: Option<usize>,
+    pub wait_ms: Option<u64>,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct ProcessOutputChunk {
+    pub seq: u64,
+    pub stream: ExecOutputStream,
+    pub chunk: ByteChunk,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct ReadResponse {
+    pub chunks: Vec<ProcessOutputChunk>,
+    pub next_seq: u64,
+    pub exited: bool,
+    pub exit_code: Option<i32>,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct WriteParams {
+    pub process_id: String,
+    pub chunk: ByteChunk,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct WriteResponse {
+    pub accepted: bool,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct TerminateParams {
+    pub process_id: String,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct TerminateResponse {
+    pub running: bool,
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub enum ExecOutputStream {
+    Stdout,
+    Stderr,
+    Pty,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct ExecOutputDeltaNotification {
+    pub process_id: String,
+    pub stream: ExecOutputStream,
+    pub chunk: ByteChunk,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct ExecExitedNotification {
+    pub process_id: String,
+    pub exit_code: i32,
+}
+
+mod base64_bytes {
+    use super::BASE64_STANDARD;
+    use base64::Engine as _;
+    use serde::Deserialize;
+    use serde::Deserializer;
+    use serde::Serializer;
+
+    pub fn serialize<S>(bytes: &[u8], serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        serializer.serialize_str(&BASE64_STANDARD.encode(bytes))
+    }
+
+    pub fn deserialize<'de, D>(deserializer: D) -> Result<Vec<u8>, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        let encoded = String::deserialize(deserializer)?;
+        BASE64_STANDARD
+            .decode(encoded)
+            .map_err(serde::de::Error::custom)
+    }
+}

codex-rs/exec-server/src/server.rs

@@ -0,0 +1,21 @@
+mod filesystem;
+mod handler;
+mod processor;
+mod routing;
+mod transport;
+
+pub(crate) use handler::ExecServerHandler;
+pub(crate) use routing::ExecServerOutboundMessage;
+pub(crate) use routing::ExecServerServerNotification;
+pub use transport::ExecServerTransport;
+pub use transport::ExecServerTransportParseError;
+
+pub async fn run_main() -> Result<(), Box<dyn std::error::Error + Send + Sync>> {
+    run_main_with_transport(ExecServerTransport::Stdio).await
+}
+
+pub async fn run_main_with_transport(
+    transport: ExecServerTransport,
+) -> Result<(), Box<dyn std::error::Error + Send + Sync>> {
+    transport::run_transport(transport).await
+}

codex-rs/exec-server/src/server/filesystem.rs

@@ -0,0 +1,170 @@
+use std::io;
+use std::sync::Arc;
+
+use base64::Engine as _;
+use base64::engine::general_purpose::STANDARD;
+use codex_app_server_protocol::FsCopyParams;
+use codex_app_server_protocol::FsCopyResponse;
+use codex_app_server_protocol::FsCreateDirectoryParams;
+use codex_app_server_protocol::FsCreateDirectoryResponse;
+use codex_app_server_protocol::FsGetMetadataParams;
+use codex_app_server_protocol::FsGetMetadataResponse;
+use codex_app_server_protocol::FsReadDirectoryEntry;
+use codex_app_server_protocol::FsReadDirectoryParams;
+use codex_app_server_protocol::FsReadDirectoryResponse;
+use codex_app_server_protocol::FsReadFileParams;
+use codex_app_server_protocol::FsReadFileResponse;
+use codex_app_server_protocol::FsRemoveParams;
+use codex_app_server_protocol::FsRemoveResponse;
+use codex_app_server_protocol::FsWriteFileParams;
+use codex_app_server_protocol::FsWriteFileResponse;
+use codex_app_server_protocol::JSONRPCErrorError;
+use codex_environment::CopyOptions;
+use codex_environment::CreateDirectoryOptions;
+use codex_environment::Environment;
+use codex_environment::ExecutorFileSystem;
+use codex_environment::RemoveOptions;
+
+use crate::server::routing::internal_error;
+use crate::server::routing::invalid_request;
+
+#[derive(Clone)]
+pub(crate) struct ExecServerFileSystem {
+    file_system: Arc<dyn ExecutorFileSystem>,
+}
+
+impl Default for ExecServerFileSystem {
+    fn default() -> Self {
+        Self {
+            file_system: Environment::default().get_filesystem(),
+        }
+    }
+}
+
+impl ExecServerFileSystem {
+    pub(crate) async fn read_file(
+        &self,
+        params: FsReadFileParams,
+    ) -> Result<FsReadFileResponse, JSONRPCErrorError> {
+        let bytes = self
+            .file_system
+            .read_file(&params.path)
+            .await
+            .map_err(map_fs_error)?;
+        Ok(FsReadFileResponse {
+            data_base64: STANDARD.encode(bytes),
+        })
+    }
+
+    pub(crate) async fn write_file(
+        &self,
+        params: FsWriteFileParams,
+    ) -> Result<FsWriteFileResponse, JSONRPCErrorError> {
+        let bytes = STANDARD.decode(params.data_base64).map_err(|err| {
+            invalid_request(format!(
+                "fs/writeFile requires valid base64 dataBase64: {err}"
+            ))
+        })?;
+        self.file_system
+            .write_file(&params.path, bytes)
+            .await
+            .map_err(map_fs_error)?;
+        Ok(FsWriteFileResponse {})
+    }
+
+    pub(crate) async fn create_directory(
+        &self,
+        params: FsCreateDirectoryParams,
+    ) -> Result<FsCreateDirectoryResponse, JSONRPCErrorError> {
+        self.file_system
+            .create_directory(
+                &params.path,
+                CreateDirectoryOptions {
+                    recursive: params.recursive.unwrap_or(true),
+                },
+            )
+            .await
+            .map_err(map_fs_error)?;
+        Ok(FsCreateDirectoryResponse {})
+    }
+
+    pub(crate) async fn get_metadata(
+        &self,
+        params: FsGetMetadataParams,
+    ) -> Result<FsGetMetadataResponse, JSONRPCErrorError> {
+        let metadata = self
+            .file_system
+            .get_metadata(&params.path)
+            .await
+            .map_err(map_fs_error)?;
+        Ok(FsGetMetadataResponse {
+            is_directory: metadata.is_directory,
+            is_file: metadata.is_file,
+            created_at_ms: metadata.created_at_ms,
+            modified_at_ms: metadata.modified_at_ms,
+        })
+    }
+
+    pub(crate) async fn read_directory(
+        &self,
+        params: FsReadDirectoryParams,
+    ) -> Result<FsReadDirectoryResponse, JSONRPCErrorError> {
+        let entries = self
+            .file_system
+            .read_directory(&params.path)
+            .await
+            .map_err(map_fs_error)?;
+        Ok(FsReadDirectoryResponse {
+            entries: entries
+                .into_iter()
+                .map(|entry| FsReadDirectoryEntry {
+                    file_name: entry.file_name,
+                    is_directory: entry.is_directory,
+                    is_file: entry.is_file,
+                })
+                .collect(),
+        })
+    }
+
+    pub(crate) async fn remove(
+        &self,
+        params: FsRemoveParams,
+    ) -> Result<FsRemoveResponse, JSONRPCErrorError> {
+        self.file_system
+            .remove(
+                &params.path,
+                RemoveOptions {
+                    recursive: params.recursive.unwrap_or(true),
+                    force: params.force.unwrap_or(true),
+                },
+            )
+            .await
+            .map_err(map_fs_error)?;
+        Ok(FsRemoveResponse {})
+    }
+
+    pub(crate) async fn copy(
+        &self,
+        params: FsCopyParams,
+    ) -> Result<FsCopyResponse, JSONRPCErrorError> {
+        self.file_system
+            .copy(
+                &params.source_path,
+                &params.destination_path,
+                CopyOptions {
+                    recursive: params.recursive,
+                },
+            )
+            .await
+            .map_err(map_fs_error)?;
+        Ok(FsCopyResponse {})
+    }
+}
+
+fn map_fs_error(err: io::Error) -> JSONRPCErrorError {
+    if err.kind() == io::ErrorKind::InvalidInput {
+        invalid_request(err.to_string())
+    } else {
+        internal_error(err.to_string())
+    }
+}

codex-rs/exec-server/src/server/handler.rs

@@ -0,0 +1,597 @@
+use std::collections::HashMap;
+use std::collections::VecDeque;
+use std::sync::Arc;
+use std::time::Duration;
+
+use codex_app_server_protocol::FsCopyParams;
+use codex_app_server_protocol::FsCopyResponse;
+use codex_app_server_protocol::FsCreateDirectoryParams;
+use codex_app_server_protocol::FsCreateDirectoryResponse;
+use codex_app_server_protocol::FsGetMetadataParams;
+use codex_app_server_protocol::FsGetMetadataResponse;
+use codex_app_server_protocol::FsReadDirectoryParams;
+use codex_app_server_protocol::FsReadDirectoryResponse;
+use codex_app_server_protocol::FsReadFileParams;
+use codex_app_server_protocol::FsReadFileResponse;
+use codex_app_server_protocol::FsRemoveParams;
+use codex_app_server_protocol::FsRemoveResponse;
+use codex_app_server_protocol::FsWriteFileParams;
+use codex_app_server_protocol::FsWriteFileResponse;
+use codex_utils_pty::ExecCommandSession;
+use codex_utils_pty::TerminalSize;
+use tokio::sync::Mutex;
+use tokio::sync::Notify;
+use tokio::sync::mpsc;
+use tracing::warn;
+
+use crate::protocol::ExecExitedNotification;
+use crate::protocol::ExecOutputDeltaNotification;
+use crate::protocol::ExecOutputStream;
+use crate::protocol::ExecResponse;
+use crate::protocol::ExecSandboxMode;
+use crate::protocol::InitializeResponse;
+use crate::protocol::PROTOCOL_VERSION;
+use crate::protocol::ProcessOutputChunk;
+use crate::protocol::ReadResponse;
+use crate::protocol::TerminateResponse;
+use crate::protocol::WriteResponse;
+use crate::server::filesystem::ExecServerFileSystem;
+use crate::server::routing::ExecServerClientNotification;
+use crate::server::routing::ExecServerInboundMessage;
+use crate::server::routing::ExecServerOutboundMessage;
+use crate::server::routing::ExecServerRequest;
+use crate::server::routing::ExecServerResponseMessage;
+use crate::server::routing::ExecServerServerNotification;
+use crate::server::routing::internal_error;
+use crate::server::routing::invalid_params;
+use crate::server::routing::invalid_request;
+
+const RETAINED_OUTPUT_BYTES_PER_PROCESS: usize = 1024 * 1024;
+#[cfg(test)]
+const EXITED_PROCESS_RETENTION: Duration = Duration::from_millis(25);
+#[cfg(not(test))]
+const EXITED_PROCESS_RETENTION: Duration = Duration::from_secs(30);
+
+#[derive(Clone)]
+struct RetainedOutputChunk {
+    seq: u64,
+    stream: ExecOutputStream,
+    chunk: Vec<u8>,
+}
+
+struct RunningProcess {
+    session: ExecCommandSession,
+    tty: bool,
+    output: VecDeque<RetainedOutputChunk>,
+    retained_bytes: usize,
+    next_seq: u64,
+    exit_code: Option<i32>,
+    output_notify: Arc<Notify>,
+}
+
+pub(crate) struct ExecServerHandler {
+    outbound_tx: mpsc::Sender<ExecServerOutboundMessage>,
+    file_system: ExecServerFileSystem,
+    // Keyed by client-chosen logical `processId` scoped to this connection.
+    // This is a protocol handle, not an OS pid.
+    processes: Arc<Mutex<HashMap<String, RunningProcess>>>,
+    initialize_requested: bool,
+    initialized: bool,
+}
+
+impl ExecServerHandler {
+    pub(crate) fn new(outbound_tx: mpsc::Sender<ExecServerOutboundMessage>) -> Self {
+        Self {
+            outbound_tx,
+            file_system: ExecServerFileSystem::default(),
+            processes: Arc::new(Mutex::new(HashMap::new())),
+            initialize_requested: false,
+            initialized: false,
+        }
+    }
+
+    pub(crate) async fn shutdown(&self) {
+        let remaining = {
+            let mut processes = self.processes.lock().await;
+            processes
+                .drain()
+                .map(|(_, process)| process)
+                .collect::<Vec<_>>()
+        };
+        for process in remaining {
+            process.session.terminate();
+        }
+    }
+
+    pub(crate) fn initialized(&mut self) -> Result<(), String> {
+        if !self.initialize_requested {
+            return Err("received `initialized` notification before `initialize`".into());
+        }
+        self.initialized = true;
+        Ok(())
+    }
+
+    pub(crate) fn initialize(
+        &mut self,
+    ) -> Result<InitializeResponse, codex_app_server_protocol::JSONRPCErrorError> {
+        if self.initialize_requested {
+            return Err(invalid_request(
+                "initialize may only be sent once per connection".to_string(),
+            ));
+        }
+        self.initialize_requested = true;
+        Ok(InitializeResponse {
+            protocol_version: PROTOCOL_VERSION.to_string(),
+        })
+    }
+
+    fn require_initialized(&self) -> Result<(), codex_app_server_protocol::JSONRPCErrorError> {
+        if !self.initialize_requested {
+            return Err(invalid_request(
+                "client must call initialize before using exec methods".to_string(),
+            ));
+        }
+        if !self.initialized {
+            return Err(invalid_request(
+                "client must send initialized before using exec methods".to_string(),
+            ));
+        }
+        Ok(())
+    }
+
+    pub(crate) async fn exec(
+        &self,
+        params: crate::protocol::ExecParams,
+    ) -> Result<ExecResponse, codex_app_server_protocol::JSONRPCErrorError> {
+        self.require_initialized()?;
+        let process_id = params.process_id.clone();
+        // Same-connection requests are serialized by the RPC processor, and the
+        // in-process client holds the handler mutex across this full call. That
+        // makes this pre-spawn duplicate check safe for the current entrypoints.
+        {
+            let process_map = self.processes.lock().await;
+            if process_map.contains_key(&process_id) {
+                return Err(invalid_request(format!(
+                    "process {process_id} already exists"
+                )));
+            }
+        }
+
+        if matches!(
+            params.sandbox.as_ref().map(|sandbox| sandbox.mode),
+            Some(ExecSandboxMode::HostDefault)
+        ) {
+            return Err(invalid_request(
+                "sandbox mode `hostDefault` is not supported by exec-server yet".to_string(),
+            ));
+        }
+
+        let (program, args) = params
+            .argv
+            .split_first()
+            .ok_or_else(|| invalid_params("argv must not be empty".to_string()))?;
+
+        let spawned = if params.tty {
+            codex_utils_pty::spawn_pty_process(
+                program,
+                args,
+                params.cwd.as_path(),
+                &params.env,
+                &params.arg0,
+                TerminalSize::default(),
+            )
+            .await
+        } else {
+            codex_utils_pty::spawn_pipe_process_no_stdin(
+                program,
+                args,
+                params.cwd.as_path(),
+                &params.env,
+                &params.arg0,
+            )
+            .await
+        }
+        .map_err(|err| internal_error(err.to_string()))?;
+
+        let output_notify = Arc::new(Notify::new());
+        {
+            let mut process_map = self.processes.lock().await;
+            process_map.insert(
+                process_id.clone(),
+                RunningProcess {
+                    session: spawned.session,
+                    tty: params.tty,
+                    output: std::collections::VecDeque::new(),
+                    retained_bytes: 0,
+                    next_seq: 1,
+                    exit_code: None,
+                    output_notify: Arc::clone(&output_notify),
+                },
+            );
+        }
+
+        tokio::spawn(stream_output(
+            process_id.clone(),
+            if params.tty {
+                ExecOutputStream::Pty
+            } else {
+                ExecOutputStream::Stdout
+            },
+            spawned.stdout_rx,
+            self.outbound_tx.clone(),
+            Arc::clone(&self.processes),
+            Arc::clone(&output_notify),
+        ));
+        tokio::spawn(stream_output(
+            process_id.clone(),
+            if params.tty {
+                ExecOutputStream::Pty
+            } else {
+                ExecOutputStream::Stderr
+            },
+            spawned.stderr_rx,
+            self.outbound_tx.clone(),
+            Arc::clone(&self.processes),
+            Arc::clone(&output_notify),
+        ));
+        tokio::spawn(watch_exit(
+            process_id.clone(),
+            spawned.exit_rx,
+            self.outbound_tx.clone(),
+            Arc::clone(&self.processes),
+            output_notify,
+        ));
+
+        Ok(ExecResponse { process_id })
+    }
+
+    pub(crate) async fn fs_read_file(
+        &self,
+        params: FsReadFileParams,
+    ) -> Result<FsReadFileResponse, codex_app_server_protocol::JSONRPCErrorError> {
+        self.require_initialized()?;
+        self.file_system.read_file(params).await
+    }
+
+    pub(crate) async fn fs_write_file(
+        &self,
+        params: FsWriteFileParams,
+    ) -> Result<FsWriteFileResponse, codex_app_server_protocol::JSONRPCErrorError> {
+        self.require_initialized()?;
+        self.file_system.write_file(params).await
+    }
+
+    pub(crate) async fn fs_create_directory(
+        &self,
+        params: FsCreateDirectoryParams,
+    ) -> Result<FsCreateDirectoryResponse, codex_app_server_protocol::JSONRPCErrorError> {
+        self.require_initialized()?;
+        self.file_system.create_directory(params).await
+    }
+
+    pub(crate) async fn fs_get_metadata(
+        &self,
+        params: FsGetMetadataParams,
+    ) -> Result<FsGetMetadataResponse, codex_app_server_protocol::JSONRPCErrorError> {
+        self.require_initialized()?;
+        self.file_system.get_metadata(params).await
+    }
+
+    pub(crate) async fn fs_read_directory(
+        &self,
+        params: FsReadDirectoryParams,
+    ) -> Result<FsReadDirectoryResponse, codex_app_server_protocol::JSONRPCErrorError> {
+        self.require_initialized()?;
+        self.file_system.read_directory(params).await
+    }
+
+    pub(crate) async fn fs_remove(
+        &self,
+        params: FsRemoveParams,
+    ) -> Result<FsRemoveResponse, codex_app_server_protocol::JSONRPCErrorError> {
+        self.require_initialized()?;
+        self.file_system.remove(params).await
+    }
+
+    pub(crate) async fn fs_copy(
+        &self,
+        params: FsCopyParams,
+    ) -> Result<FsCopyResponse, codex_app_server_protocol::JSONRPCErrorError> {
+        self.require_initialized()?;
+        self.file_system.copy(params).await
+    }
+
+    pub(crate) async fn exec_read(
+        &self,
+        params: crate::protocol::ReadParams,
+    ) -> Result<ReadResponse, codex_app_server_protocol::JSONRPCErrorError> {
+        self.require_initialized()?;
+        let after_seq = params.after_seq.unwrap_or(0);
+        let max_bytes = params.max_bytes.unwrap_or(usize::MAX);
+        let wait = Duration::from_millis(params.wait_ms.unwrap_or(0));
+        let deadline = tokio::time::Instant::now() + wait;
+
+        loop {
+            let (response, output_notify) = {
+                let process_map = self.processes.lock().await;
+                let process = process_map.get(&params.process_id).ok_or_else(|| {
+                    invalid_request(format!("unknown process id {}", params.process_id))
+                })?;
+
+                let mut chunks = Vec::new();
+                let mut total_bytes = 0;
+                let mut next_seq = process.next_seq;
+                for retained in process.output.iter().filter(|chunk| chunk.seq > after_seq) {
+                    let chunk_len = retained.chunk.len();
+                    if !chunks.is_empty() && total_bytes + chunk_len > max_bytes {
+                        break;
+                    }
+                    total_bytes += chunk_len;
+                    chunks.push(ProcessOutputChunk {
+                        seq: retained.seq,
+                        stream: retained.stream,
+                        chunk: retained.chunk.clone().into(),
+                    });
+                    next_seq = retained.seq + 1;
+                    if total_bytes >= max_bytes {
+                        break;
+                    }
+                }
+
+                (
+                    ReadResponse {
+                        chunks,
+                        next_seq,
+                        exited: process.exit_code.is_some(),
+                        exit_code: process.exit_code,
+                    },
+                    Arc::clone(&process.output_notify),
+                )
+            };
+
+            if !response.chunks.is_empty()
+                || response.exited
+                || tokio::time::Instant::now() >= deadline
+            {
+                return Ok(response);
+            }
+
+            let remaining = deadline.saturating_duration_since(tokio::time::Instant::now());
+            if remaining.is_zero() {
+                return Ok(response);
+            }
+            let _ = tokio::time::timeout(remaining, output_notify.notified()).await;
+        }
+    }
+
+    pub(crate) async fn exec_write(
+        &self,
+        params: crate::protocol::WriteParams,
+    ) -> Result<WriteResponse, codex_app_server_protocol::JSONRPCErrorError> {
+        self.require_initialized()?;
+        let writer_tx = {
+            let process_map = self.processes.lock().await;
+            let process = process_map.get(&params.process_id).ok_or_else(|| {
+                invalid_request(format!("unknown process id {}", params.process_id))
+            })?;
+            if !process.tty {
+                return Err(invalid_request(format!(
+                    "stdin is closed for process {}",
+                    params.process_id
+                )));
+            }
+            process.session.writer_sender()
+        };
+
+        writer_tx
+            .send(params.chunk.into_inner())
+            .await
+            .map_err(|_| internal_error("failed to write to process stdin".to_string()))?;
+
+        Ok(WriteResponse { accepted: true })
+    }
+
+    pub(crate) async fn terminate(
+        &self,
+        params: crate::protocol::TerminateParams,
+    ) -> Result<TerminateResponse, codex_app_server_protocol::JSONRPCErrorError> {
+        self.require_initialized()?;
+        let running = {
+            let process_map = self.processes.lock().await;
+            if let Some(process) = process_map.get(&params.process_id) {
+                process.session.terminate();
+                true
+            } else {
+                false
+            }
+        };
+
+        Ok(TerminateResponse { running })
+    }
+
+    pub(crate) async fn handle_message(
+        &mut self,
+        message: ExecServerInboundMessage,
+    ) -> Result<(), String> {
+        match message {
+            ExecServerInboundMessage::Request(request) => self.handle_request(request).await,
+            ExecServerInboundMessage::Notification(ExecServerClientNotification::Initialized) => {
+                self.initialized()
+            }
+        }
+    }
+
+    async fn handle_request(&mut self, request: ExecServerRequest) -> Result<(), String> {
+        let outbound = match request {
+            ExecServerRequest::Initialize { request_id, .. } => Self::request_outbound(
+                request_id,
+                self.initialize().map(ExecServerResponseMessage::Initialize),
+            ),
+            ExecServerRequest::Exec { request_id, params } => Self::request_outbound(
+                request_id,
+                self.exec(params).await.map(ExecServerResponseMessage::Exec),
+            ),
+            ExecServerRequest::Read { request_id, params } => Self::request_outbound(
+                request_id,
+                self.exec_read(params)
+                    .await
+                    .map(ExecServerResponseMessage::Read),
+            ),
+            ExecServerRequest::Write { request_id, params } => Self::request_outbound(
+                request_id,
+                self.exec_write(params)
+                    .await
+                    .map(ExecServerResponseMessage::Write),
+            ),
+            ExecServerRequest::Terminate { request_id, params } => Self::request_outbound(
+                request_id,
+                self.terminate(params)
+                    .await
+                    .map(ExecServerResponseMessage::Terminate),
+            ),
+            ExecServerRequest::FsReadFile { request_id, params } => Self::request_outbound(
+                request_id,
+                self.fs_read_file(params)
+                    .await
+                    .map(ExecServerResponseMessage::FsReadFile),
+            ),
+            ExecServerRequest::FsWriteFile { request_id, params } => Self::request_outbound(
+                request_id,
+                self.fs_write_file(params)
+                    .await
+                    .map(ExecServerResponseMessage::FsWriteFile),
+            ),
+            ExecServerRequest::FsCreateDirectory { request_id, params } => Self::request_outbound(
+                request_id,
+                self.fs_create_directory(params)
+                    .await
+                    .map(ExecServerResponseMessage::FsCreateDirectory),
+            ),
+            ExecServerRequest::FsGetMetadata { request_id, params } => Self::request_outbound(
+                request_id,
+                self.fs_get_metadata(params)
+                    .await
+                    .map(ExecServerResponseMessage::FsGetMetadata),
+            ),
+            ExecServerRequest::FsReadDirectory { request_id, params } => Self::request_outbound(
+                request_id,
+                self.fs_read_directory(params)
+                    .await
+                    .map(ExecServerResponseMessage::FsReadDirectory),
+            ),
+            ExecServerRequest::FsRemove { request_id, params } => Self::request_outbound(
+                request_id,
+                self.fs_remove(params)
+                    .await
+                    .map(ExecServerResponseMessage::FsRemove),
+            ),
+            ExecServerRequest::FsCopy { request_id, params } => Self::request_outbound(
+                request_id,
+                self.fs_copy(params)
+                    .await
+                    .map(ExecServerResponseMessage::FsCopy),
+            ),
+        };
+        self.outbound_tx
+            .send(outbound)
+            .await
+            .map_err(|_| "outbound channel closed".to_string())
+    }
+
+    fn request_outbound(
+        request_id: codex_app_server_protocol::RequestId,
+        result: Result<ExecServerResponseMessage, codex_app_server_protocol::JSONRPCErrorError>,
+    ) -> ExecServerOutboundMessage {
+        match result {
+            Ok(response) => ExecServerOutboundMessage::Response {
+                request_id,
+                response,
+            },
+            Err(error) => ExecServerOutboundMessage::Error { request_id, error },
+        }
+    }
+}
+
+async fn stream_output(
+    process_id: String,
+    stream: ExecOutputStream,
+    mut receiver: tokio::sync::mpsc::Receiver<Vec<u8>>,
+    outbound_tx: mpsc::Sender<ExecServerOutboundMessage>,
+    processes: Arc<Mutex<HashMap<String, RunningProcess>>>,
+    output_notify: Arc<Notify>,
+) {
+    while let Some(chunk) = receiver.recv().await {
+        let notification = {
+            let mut processes = processes.lock().await;
+            let Some(process) = processes.get_mut(&process_id) else {
+                break;
+            };
+            let seq = process.next_seq;
+            process.next_seq += 1;
+            process.retained_bytes += chunk.len();
+            process.output.push_back(RetainedOutputChunk {
+                seq,
+                stream,
+                chunk: chunk.clone(),
+            });
+            while process.retained_bytes > RETAINED_OUTPUT_BYTES_PER_PROCESS {
+                let Some(evicted) = process.output.pop_front() else {
+                    break;
+                };
+                process.retained_bytes = process.retained_bytes.saturating_sub(evicted.chunk.len());
+                warn!(
+                    "retained output cap exceeded for process {process_id}; dropping oldest output"
+                );
+            }
+            ExecOutputDeltaNotification {
+                process_id: process_id.clone(),
+                stream,
+                chunk: chunk.into(),
+            }
+        };
+        output_notify.notify_waiters();
+
+        if outbound_tx
+            .send(ExecServerOutboundMessage::Notification(
+                ExecServerServerNotification::OutputDelta(notification),
+            ))
+            .await
+            .is_err()
+        {
+            break;
+        }
+    }
+}
+
+async fn watch_exit(
+    process_id: String,
+    exit_rx: tokio::sync::oneshot::Receiver<i32>,
+    outbound_tx: mpsc::Sender<ExecServerOutboundMessage>,
+    processes: Arc<Mutex<HashMap<String, RunningProcess>>>,
+    output_notify: Arc<Notify>,
+) {
+    let exit_code = exit_rx.await.unwrap_or(-1);
+    {
+        let mut processes = processes.lock().await;
+        if let Some(process) = processes.get_mut(&process_id) {
+            process.exit_code = Some(exit_code);
+        }
+    }
+    output_notify.notify_waiters();
+    let _ = outbound_tx
+        .send(ExecServerOutboundMessage::Notification(
+            ExecServerServerNotification::Exited(ExecExitedNotification {
+                process_id: process_id.clone(),
+                exit_code,
+            }),
+        ))
+        .await;
+    tokio::spawn(async move {
+        tokio::time::sleep(EXITED_PROCESS_RETENTION).await;
+        let mut processes = processes.lock().await;
+        processes.remove(&process_id);
+    });
+}
+
+#[cfg(test)]
+mod tests;

codex-rs/exec-server/src/server/handler/tests.rs

@@ -0,0 +1,734 @@
+use std::collections::HashMap;
+use std::collections::VecDeque;
+use std::sync::Arc;
+use std::time::Duration;
+
+use pretty_assertions::assert_eq;
+use tokio::sync::Notify;
+use tokio::time::timeout;
+
+use super::ExecServerHandler;
+use super::RetainedOutputChunk;
+use super::RunningProcess;
+use crate::protocol::ExecOutputStream;
+use crate::protocol::ExecSandboxConfig;
+use crate::protocol::ExecSandboxMode;
+use crate::protocol::InitializeParams;
+use crate::protocol::InitializeResponse;
+use crate::protocol::PROTOCOL_VERSION;
+use crate::protocol::ReadParams;
+use crate::protocol::TerminateResponse;
+use crate::protocol::WriteParams;
+use crate::server::routing::ExecServerClientNotification;
+use crate::server::routing::ExecServerInboundMessage;
+use crate::server::routing::ExecServerOutboundMessage;
+use crate::server::routing::ExecServerRequest;
+use crate::server::routing::ExecServerResponseMessage;
+use codex_app_server_protocol::RequestId;
+
+async fn recv_outbound(
+    outgoing_rx: &mut tokio::sync::mpsc::Receiver<ExecServerOutboundMessage>,
+) -> ExecServerOutboundMessage {
+    let recv_result = timeout(Duration::from_secs(1), outgoing_rx.recv()).await;
+    let maybe_message = match recv_result {
+        Ok(maybe_message) => maybe_message,
+        Err(err) => panic!("timed out waiting for handler output: {err}"),
+    };
+    match maybe_message {
+        Some(message) => message,
+        None => panic!("handler output channel closed unexpectedly"),
+    }
+}
+
+#[tokio::test]
+async fn initialize_response_reports_protocol_version() {
+    let (outgoing_tx, mut outgoing_rx) = tokio::sync::mpsc::channel(1);
+    let mut handler = ExecServerHandler::new(outgoing_tx);
+
+    if let Err(err) = handler
+        .handle_message(ExecServerInboundMessage::Request(
+            ExecServerRequest::Initialize {
+                request_id: RequestId::Integer(1),
+                params: InitializeParams {
+                    client_name: "test".to_string(),
+                },
+            },
+        ))
+        .await
+    {
+        panic!("initialize should succeed: {err}");
+    }
+
+    assert_eq!(
+        recv_outbound(&mut outgoing_rx).await,
+        ExecServerOutboundMessage::Response {
+            request_id: RequestId::Integer(1),
+            response: ExecServerResponseMessage::Initialize(InitializeResponse {
+                protocol_version: PROTOCOL_VERSION.to_string(),
+            }),
+        }
+    );
+}
+
+#[tokio::test]
+async fn exec_methods_require_initialize() {
+    let (outgoing_tx, mut outgoing_rx) = tokio::sync::mpsc::channel(1);
+    let mut handler = ExecServerHandler::new(outgoing_tx);
+
+    if let Err(err) = handler
+        .handle_message(ExecServerInboundMessage::Request(ExecServerRequest::Exec {
+            request_id: RequestId::Integer(7),
+            params: crate::protocol::ExecParams {
+                process_id: "proc-1".to_string(),
+                argv: vec!["bash".to_string(), "-lc".to_string(), "true".to_string()],
+                cwd: std::env::current_dir().expect("cwd"),
+                env: HashMap::new(),
+                tty: true,
+                arg0: None,
+                sandbox: None,
+            },
+        }))
+        .await
+    {
+        panic!("request handling should not fail the handler: {err}");
+    }
+
+    let ExecServerOutboundMessage::Error { request_id, error } =
+        recv_outbound(&mut outgoing_rx).await
+    else {
+        panic!("expected invalid-request error");
+    };
+    assert_eq!(request_id, RequestId::Integer(7));
+    assert_eq!(error.code, -32600);
+    assert_eq!(
+        error.message,
+        "client must call initialize before using exec methods"
+    );
+}
+
+#[tokio::test]
+async fn exec_methods_require_initialized_notification_after_initialize() {
+    let (outgoing_tx, mut outgoing_rx) = tokio::sync::mpsc::channel(2);
+    let mut handler = ExecServerHandler::new(outgoing_tx);
+
+    if let Err(err) = handler
+        .handle_message(ExecServerInboundMessage::Request(
+            ExecServerRequest::Initialize {
+                request_id: RequestId::Integer(1),
+                params: InitializeParams {
+                    client_name: "test".to_string(),
+                },
+            },
+        ))
+        .await
+    {
+        panic!("initialize should succeed: {err}");
+    }
+    let _ = recv_outbound(&mut outgoing_rx).await;
+
+    if let Err(err) = handler
+        .handle_message(ExecServerInboundMessage::Request(ExecServerRequest::Exec {
+            request_id: RequestId::Integer(2),
+            params: crate::protocol::ExecParams {
+                process_id: "proc-1".to_string(),
+                argv: vec!["bash".to_string(), "-lc".to_string(), "true".to_string()],
+                cwd: std::env::current_dir().expect("cwd"),
+                env: HashMap::new(),
+                tty: true,
+                arg0: None,
+                sandbox: None,
+            },
+        }))
+        .await
+    {
+        panic!("request handling should not fail the handler: {err}");
+    }
+
+    let ExecServerOutboundMessage::Error { request_id, error } =
+        recv_outbound(&mut outgoing_rx).await
+    else {
+        panic!("expected invalid-request error");
+    };
+    assert_eq!(request_id, RequestId::Integer(2));
+    assert_eq!(error.code, -32600);
+    assert_eq!(
+        error.message,
+        "client must send initialized before using exec methods"
+    );
+}
+
+#[tokio::test]
+async fn initialized_before_initialize_is_a_protocol_error() {
+    let (outgoing_tx, _outgoing_rx) = tokio::sync::mpsc::channel(1);
+    let mut handler = ExecServerHandler::new(outgoing_tx);
+
+    let result = handler
+        .handle_message(ExecServerInboundMessage::Notification(
+            ExecServerClientNotification::Initialized,
+        ))
+        .await;
+
+    match result {
+        Err(err) => {
+            assert_eq!(
+                err,
+                "received `initialized` notification before `initialize`"
+            );
+        }
+        Ok(()) => panic!("expected protocol error for early initialized notification"),
+    }
+}
+
+#[tokio::test]
+async fn initialize_may_only_be_sent_once_per_connection() {
+    let (outgoing_tx, mut outgoing_rx) = tokio::sync::mpsc::channel(2);
+    let mut handler = ExecServerHandler::new(outgoing_tx);
+
+    if let Err(err) = handler
+        .handle_message(ExecServerInboundMessage::Request(
+            ExecServerRequest::Initialize {
+                request_id: RequestId::Integer(1),
+                params: InitializeParams {
+                    client_name: "test".to_string(),
+                },
+            },
+        ))
+        .await
+    {
+        panic!("initialize should succeed: {err}");
+    }
+    let _ = recv_outbound(&mut outgoing_rx).await;
+
+    if let Err(err) = handler
+        .handle_message(ExecServerInboundMessage::Request(
+            ExecServerRequest::Initialize {
+                request_id: RequestId::Integer(2),
+                params: InitializeParams {
+                    client_name: "test".to_string(),
+                },
+            },
+        ))
+        .await
+    {
+        panic!("duplicate initialize should not fail the handler: {err}");
+    }
+
+    let ExecServerOutboundMessage::Error { request_id, error } =
+        recv_outbound(&mut outgoing_rx).await
+    else {
+        panic!("expected invalid-request error");
+    };
+    assert_eq!(request_id, RequestId::Integer(2));
+    assert_eq!(error.code, -32600);
+    assert_eq!(
+        error.message,
+        "initialize may only be sent once per connection"
+    );
+}
+
+#[tokio::test]
+async fn host_default_sandbox_requests_are_rejected_until_supported() {
+    let (outgoing_tx, mut outgoing_rx) = tokio::sync::mpsc::channel(3);
+    let mut handler = ExecServerHandler::new(outgoing_tx);
+
+    if let Err(err) = handler
+        .handle_message(ExecServerInboundMessage::Request(
+            ExecServerRequest::Initialize {
+                request_id: RequestId::Integer(1),
+                params: InitializeParams {
+                    client_name: "test".to_string(),
+                },
+            },
+        ))
+        .await
+    {
+        panic!("initialize should succeed: {err}");
+    }
+    let _ = recv_outbound(&mut outgoing_rx).await;
+    if let Err(err) = handler
+        .handle_message(ExecServerInboundMessage::Notification(
+            ExecServerClientNotification::Initialized,
+        ))
+        .await
+    {
+        panic!("initialized should succeed: {err}");
+    }
+
+    if let Err(err) = handler
+        .handle_message(ExecServerInboundMessage::Request(ExecServerRequest::Exec {
+            request_id: RequestId::Integer(2),
+            params: crate::protocol::ExecParams {
+                process_id: "proc-1".to_string(),
+                argv: vec!["bash".to_string(), "-lc".to_string(), "true".to_string()],
+                cwd: std::env::current_dir().expect("cwd"),
+                env: HashMap::new(),
+                tty: false,
+                arg0: None,
+                sandbox: Some(ExecSandboxConfig {
+                    mode: ExecSandboxMode::HostDefault,
+                }),
+            },
+        }))
+        .await
+    {
+        panic!("request handling should not fail the handler: {err}");
+    }
+
+    let ExecServerOutboundMessage::Error { request_id, error } =
+        recv_outbound(&mut outgoing_rx).await
+    else {
+        panic!("expected unsupported sandbox error");
+    };
+    assert_eq!(request_id, RequestId::Integer(2));
+    assert_eq!(error.code, -32600);
+    assert_eq!(
+        error.message,
+        "sandbox mode `hostDefault` is not supported by exec-server yet"
+    );
+}
+
+#[tokio::test]
+async fn exec_echoes_client_process_ids() {
+    let (outgoing_tx, mut outgoing_rx) = tokio::sync::mpsc::channel(4);
+    let mut handler = ExecServerHandler::new(outgoing_tx);
+
+    if let Err(err) = handler
+        .handle_message(ExecServerInboundMessage::Request(
+            ExecServerRequest::Initialize {
+                request_id: RequestId::Integer(1),
+                params: InitializeParams {
+                    client_name: "test".to_string(),
+                },
+            },
+        ))
+        .await
+    {
+        panic!("initialize should succeed: {err}");
+    }
+    let _ = recv_outbound(&mut outgoing_rx).await;
+    if let Err(err) = handler
+        .handle_message(ExecServerInboundMessage::Notification(
+            ExecServerClientNotification::Initialized,
+        ))
+        .await
+    {
+        panic!("initialized should succeed: {err}");
+    }
+
+    let params = crate::protocol::ExecParams {
+        process_id: "proc-1".to_string(),
+        argv: vec![
+            "bash".to_string(),
+            "-lc".to_string(),
+            "sleep 30".to_string(),
+        ],
+        cwd: std::env::current_dir().expect("cwd"),
+        env: HashMap::new(),
+        tty: false,
+        arg0: None,
+        sandbox: None,
+    };
+    if let Err(err) = handler
+        .handle_message(ExecServerInboundMessage::Request(ExecServerRequest::Exec {
+            request_id: RequestId::Integer(2),
+            params: params.clone(),
+        }))
+        .await
+    {
+        panic!("first exec should succeed: {err}");
+    }
+    let ExecServerOutboundMessage::Response {
+        request_id,
+        response: ExecServerResponseMessage::Exec(first_exec),
+    } = recv_outbound(&mut outgoing_rx).await
+    else {
+        panic!("expected first exec response");
+    };
+    assert_eq!(request_id, RequestId::Integer(2));
+    assert_eq!(first_exec.process_id, "proc-1");
+
+    if let Err(err) = handler
+        .handle_message(ExecServerInboundMessage::Request(ExecServerRequest::Exec {
+            request_id: RequestId::Integer(3),
+            params: crate::protocol::ExecParams {
+                process_id: "proc-2".to_string(),
+                argv: vec!["bash".to_string(), "-lc".to_string(), "true".to_string()],
+                ..params
+            },
+        }))
+        .await
+    {
+        panic!("second exec should succeed: {err}");
+    }
+
+    let ExecServerOutboundMessage::Response {
+        request_id,
+        response: ExecServerResponseMessage::Exec(second_exec),
+    } = recv_outbound(&mut outgoing_rx).await
+    else {
+        panic!("expected second exec response");
+    };
+    assert_eq!(request_id, RequestId::Integer(3));
+    assert_eq!(second_exec.process_id, "proc-2");
+
+    handler.shutdown().await;
+}
+
+#[tokio::test]
+async fn writes_to_pipe_backed_processes_are_rejected() {
+    let (outgoing_tx, mut outgoing_rx) = tokio::sync::mpsc::channel(4);
+    let mut handler = ExecServerHandler::new(outgoing_tx);
+
+    if let Err(err) = handler
+        .handle_message(ExecServerInboundMessage::Request(
+            ExecServerRequest::Initialize {
+                request_id: RequestId::Integer(1),
+                params: InitializeParams {
+                    client_name: "test".to_string(),
+                },
+            },
+        ))
+        .await
+    {
+        panic!("initialize should succeed: {err}");
+    }
+    let _ = recv_outbound(&mut outgoing_rx).await;
+    if let Err(err) = handler
+        .handle_message(ExecServerInboundMessage::Notification(
+            ExecServerClientNotification::Initialized,
+        ))
+        .await
+    {
+        panic!("initialized should succeed: {err}");
+    }
+
+    if let Err(err) = handler
+        .handle_message(ExecServerInboundMessage::Request(ExecServerRequest::Exec {
+            request_id: RequestId::Integer(2),
+            params: crate::protocol::ExecParams {
+                process_id: "proc-1".to_string(),
+                argv: vec![
+                    "bash".to_string(),
+                    "-lc".to_string(),
+                    "sleep 30".to_string(),
+                ],
+                cwd: std::env::current_dir().expect("cwd"),
+                env: HashMap::new(),
+                tty: false,
+                arg0: None,
+                sandbox: None,
+            },
+        }))
+        .await
+    {
+        panic!("exec should succeed: {err}");
+    }
+    let ExecServerOutboundMessage::Response {
+        response: ExecServerResponseMessage::Exec(exec_response),
+        ..
+    } = recv_outbound(&mut outgoing_rx).await
+    else {
+        panic!("expected exec response");
+    };
+
+    if let Err(err) = handler
+        .handle_message(ExecServerInboundMessage::Request(
+            ExecServerRequest::Write {
+                request_id: RequestId::Integer(3),
+                params: WriteParams {
+                    process_id: exec_response.process_id,
+                    chunk: b"hello\n".to_vec().into(),
+                },
+            },
+        ))
+        .await
+    {
+        panic!("write should not fail the handler: {err}");
+    }
+
+    let ExecServerOutboundMessage::Error { request_id, error } =
+        recv_outbound(&mut outgoing_rx).await
+    else {
+        panic!("expected stdin-closed error");
+    };
+    assert_eq!(request_id, RequestId::Integer(3));
+    assert_eq!(error.code, -32600);
+    assert_eq!(error.message, "stdin is closed for process proc-1");
+
+    handler.shutdown().await;
+}
+
+#[tokio::test]
+async fn writes_to_unknown_processes_are_rejected() {
+    let (outgoing_tx, mut outgoing_rx) = tokio::sync::mpsc::channel(2);
+    let mut handler = ExecServerHandler::new(outgoing_tx);
+
+    if let Err(err) = handler
+        .handle_message(ExecServerInboundMessage::Request(
+            ExecServerRequest::Initialize {
+                request_id: RequestId::Integer(1),
+                params: InitializeParams {
+                    client_name: "test".to_string(),
+                },
+            },
+        ))
+        .await
+    {
+        panic!("initialize should succeed: {err}");
+    }
+    let _ = recv_outbound(&mut outgoing_rx).await;
+    if let Err(err) = handler
+        .handle_message(ExecServerInboundMessage::Notification(
+            ExecServerClientNotification::Initialized,
+        ))
+        .await
+    {
+        panic!("initialized should succeed: {err}");
+    }
+
+    if let Err(err) = handler
+        .handle_message(ExecServerInboundMessage::Request(
+            ExecServerRequest::Write {
+                request_id: RequestId::Integer(2),
+                params: WriteParams {
+                    process_id: "missing".to_string(),
+                    chunk: b"hello\n".to_vec().into(),
+                },
+            },
+        ))
+        .await
+    {
+        panic!("write should not fail the handler: {err}");
+    }
+
+    let ExecServerOutboundMessage::Error { request_id, error } =
+        recv_outbound(&mut outgoing_rx).await
+    else {
+        panic!("expected unknown-process error");
+    };
+    assert_eq!(request_id, RequestId::Integer(2));
+    assert_eq!(error.code, -32600);
+    assert_eq!(error.message, "unknown process id missing");
+}
+
+#[tokio::test]
+async fn terminate_unknown_processes_report_running_false() {
+    let (outgoing_tx, mut outgoing_rx) = tokio::sync::mpsc::channel(2);
+    let mut handler = ExecServerHandler::new(outgoing_tx);
+
+    if let Err(err) = handler
+        .handle_message(ExecServerInboundMessage::Request(
+            ExecServerRequest::Initialize {
+                request_id: RequestId::Integer(1),
+                params: InitializeParams {
+                    client_name: "test".to_string(),
+                },
+            },
+        ))
+        .await
+    {
+        panic!("initialize should succeed: {err}");
+    }
+    let _ = recv_outbound(&mut outgoing_rx).await;
+    if let Err(err) = handler
+        .handle_message(ExecServerInboundMessage::Notification(
+            ExecServerClientNotification::Initialized,
+        ))
+        .await
+    {
+        panic!("initialized should succeed: {err}");
+    }
+
+    if let Err(err) = handler
+        .handle_message(ExecServerInboundMessage::Request(
+            ExecServerRequest::Terminate {
+                request_id: RequestId::Integer(2),
+                params: crate::protocol::TerminateParams {
+                    process_id: "missing".to_string(),
+                },
+            },
+        ))
+        .await
+    {
+        panic!("terminate should not fail the handler: {err}");
+    }
+
+    assert_eq!(
+        recv_outbound(&mut outgoing_rx).await,
+        ExecServerOutboundMessage::Response {
+            request_id: RequestId::Integer(2),
+            response: ExecServerResponseMessage::Terminate(TerminateResponse { running: false }),
+        }
+    );
+}
+
+#[tokio::test]
+async fn terminate_keeps_process_ids_reserved() {
+    let (outgoing_tx, mut outgoing_rx) = tokio::sync::mpsc::channel(2);
+    let mut handler = ExecServerHandler::new(outgoing_tx);
+
+    if let Err(err) = handler
+        .handle_message(ExecServerInboundMessage::Request(
+            ExecServerRequest::Initialize {
+                request_id: RequestId::Integer(1),
+                params: InitializeParams {
+                    client_name: "test".to_string(),
+                },
+            },
+        ))
+        .await
+    {
+        panic!("initialize should succeed: {err}");
+    }
+    let _ = recv_outbound(&mut outgoing_rx).await;
+    if let Err(err) = handler
+        .handle_message(ExecServerInboundMessage::Notification(
+            ExecServerClientNotification::Initialized,
+        ))
+        .await
+    {
+        panic!("initialized should succeed: {err}");
+    }
+
+    if let Err(err) = handler
+        .handle_message(ExecServerInboundMessage::Request(ExecServerRequest::Exec {
+            request_id: RequestId::Integer(2),
+            params: crate::protocol::ExecParams {
+                process_id: "proc-1".to_string(),
+                argv: vec![
+                    "bash".to_string(),
+                    "-lc".to_string(),
+                    "sleep 30".to_string(),
+                ],
+                cwd: std::env::current_dir().expect("cwd"),
+                env: HashMap::new(),
+                tty: false,
+                arg0: None,
+                sandbox: None,
+            },
+        }))
+        .await
+    {
+        panic!("exec should not fail the handler: {err}");
+    }
+    let _ = recv_outbound(&mut outgoing_rx).await;
+
+    if let Err(err) = handler
+        .handle_message(ExecServerInboundMessage::Request(
+            ExecServerRequest::Terminate {
+                request_id: RequestId::Integer(3),
+                params: crate::protocol::TerminateParams {
+                    process_id: "proc-1".to_string(),
+                },
+            },
+        ))
+        .await
+    {
+        panic!("terminate should not fail the handler: {err}");
+    }
+
+    assert_eq!(
+        recv_outbound(&mut outgoing_rx).await,
+        ExecServerOutboundMessage::Response {
+            request_id: RequestId::Integer(3),
+            response: ExecServerResponseMessage::Terminate(TerminateResponse { running: true }),
+        }
+    );
+
+    assert!(
+        handler.processes.lock().await.contains_key("proc-1"),
+        "terminated ids should stay reserved until exit cleanup removes them"
+    );
+
+    let deadline = tokio::time::Instant::now() + Duration::from_secs(1);
+    loop {
+        if !handler.processes.lock().await.contains_key("proc-1") {
+            break;
+        }
+        assert!(
+            tokio::time::Instant::now() < deadline,
+            "terminated ids should be removed after the exit retention window"
+        );
+        tokio::time::sleep(Duration::from_millis(25)).await;
+    }
+
+    handler.shutdown().await;
+}
+
+#[tokio::test]
+async fn read_paginates_retained_output_without_skipping_omitted_chunks() {
+    let (outgoing_tx, _outgoing_rx) = tokio::sync::mpsc::channel(1);
+    let mut handler = ExecServerHandler::new(outgoing_tx);
+    let _ = handler.initialize().expect("initialize should succeed");
+    handler.initialized().expect("initialized should succeed");
+
+    let spawned = codex_utils_pty::spawn_pipe_process_no_stdin(
+        "bash",
+        &["-lc".to_string(), "true".to_string()],
+        std::env::current_dir().expect("cwd").as_path(),
+        &HashMap::new(),
+        &None,
+    )
+    .await
+    .expect("spawn test process");
+    {
+        let mut process_map = handler.processes.lock().await;
+        process_map.insert(
+            "proc-1".to_string(),
+            RunningProcess {
+                session: spawned.session,
+                tty: false,
+                output: VecDeque::from([
+                    RetainedOutputChunk {
+                        seq: 1,
+                        stream: ExecOutputStream::Stdout,
+                        chunk: b"abc".to_vec(),
+                    },
+                    RetainedOutputChunk {
+                        seq: 2,
+                        stream: ExecOutputStream::Stderr,
+                        chunk: b"def".to_vec(),
+                    },
+                ]),
+                retained_bytes: 6,
+                next_seq: 3,
+                exit_code: None,
+                output_notify: Arc::new(Notify::new()),
+            },
+        );
+    }
+
+    let first = handler
+        .exec_read(ReadParams {
+            process_id: "proc-1".to_string(),
+            after_seq: Some(0),
+            max_bytes: Some(3),
+            wait_ms: Some(0),
+        })
+        .await
+        .expect("first read should succeed");
+
+    assert_eq!(first.chunks.len(), 1);
+    assert_eq!(first.chunks[0].seq, 1);
+    assert_eq!(first.chunks[0].stream, ExecOutputStream::Stdout);
+    assert_eq!(first.chunks[0].chunk.clone().into_inner(), b"abc".to_vec());
+    assert_eq!(first.next_seq, 2);
+
+    let second = handler
+        .exec_read(ReadParams {
+            process_id: "proc-1".to_string(),
+            after_seq: Some(first.next_seq - 1),
+            max_bytes: Some(3),
+            wait_ms: Some(0),
+        })
+        .await
+        .expect("second read should succeed");
+
+    assert_eq!(second.chunks.len(), 1);
+    assert_eq!(second.chunks[0].seq, 2);
+    assert_eq!(second.chunks[0].stream, ExecOutputStream::Stderr);
+    assert_eq!(second.chunks[0].chunk.clone().into_inner(), b"def".to_vec());
+    assert_eq!(second.next_seq, 3);
+
+    handler.shutdown().await;
+}

codex-rs/exec-server/src/server/processor.rs

@@ -0,0 +1,67 @@
+use tokio::sync::mpsc;
+use tracing::debug;
+use tracing::warn;
+
+use crate::connection::CHANNEL_CAPACITY;
+use crate::connection::JsonRpcConnection;
+use crate::connection::JsonRpcConnectionEvent;
+use crate::server::handler::ExecServerHandler;
+use crate::server::routing::ExecServerOutboundMessage;
+use crate::server::routing::RoutedExecServerMessage;
+use crate::server::routing::encode_outbound_message;
+use crate::server::routing::route_jsonrpc_message;
+
+pub(crate) async fn run_connection(connection: JsonRpcConnection) {
+    let (json_outgoing_tx, mut incoming_rx, _connection_tasks) = connection.into_parts();
+    let (outgoing_tx, mut outgoing_rx) =
+        mpsc::channel::<ExecServerOutboundMessage>(CHANNEL_CAPACITY);
+    let mut handler = ExecServerHandler::new(outgoing_tx.clone());
+
+    let outbound_task = tokio::spawn(async move {
+        while let Some(message) = outgoing_rx.recv().await {
+            let json_message = match encode_outbound_message(message) {
+                Ok(json_message) => json_message,
+                Err(err) => {
+                    warn!("failed to serialize exec-server outbound message: {err}");
+                    break;
+                }
+            };
+            if json_outgoing_tx.send(json_message).await.is_err() {
+                break;
+            }
+        }
+    });
+
+    while let Some(event) = incoming_rx.recv().await {
+        match event {
+            JsonRpcConnectionEvent::Message(message) => match route_jsonrpc_message(message) {
+                Ok(RoutedExecServerMessage::Inbound(message)) => {
+                    if let Err(err) = handler.handle_message(message).await {
+                        warn!("closing exec-server connection after protocol error: {err}");
+                        break;
+                    }
+                }
+                Ok(RoutedExecServerMessage::ImmediateOutbound(message)) => {
+                    if outgoing_tx.send(message).await.is_err() {
+                        break;
+                    }
+                }
+                Err(err) => {
+                    warn!("closing exec-server connection after protocol error: {err}");
+                    break;
+                }
+            },
+            JsonRpcConnectionEvent::Disconnected { reason } => {
+                if let Some(reason) = reason {
+                    debug!("exec-server connection disconnected: {reason}");
+                }
+                break;
+            }
+        }
+    }
+
+    handler.shutdown().await;
+    drop(handler);
+    drop(outgoing_tx);
+    let _ = outbound_task.await;
+}

codex-rs/exec-server/src/server/routing.rs

@@ -0,0 +1,585 @@
+use codex_app_server_protocol::JSONRPCError;
+use codex_app_server_protocol::JSONRPCErrorError;
+use codex_app_server_protocol::JSONRPCMessage;
+use codex_app_server_protocol::JSONRPCNotification;
+use codex_app_server_protocol::JSONRPCRequest;
+use codex_app_server_protocol::JSONRPCResponse;
+use codex_app_server_protocol::RequestId;
+use serde::de::DeserializeOwned;
+
+use crate::protocol::EXEC_EXITED_METHOD;
+use crate::protocol::EXEC_METHOD;
+use crate::protocol::EXEC_OUTPUT_DELTA_METHOD;
+use crate::protocol::EXEC_READ_METHOD;
+use crate::protocol::EXEC_TERMINATE_METHOD;
+use crate::protocol::EXEC_WRITE_METHOD;
+use crate::protocol::ExecExitedNotification;
+use crate::protocol::ExecOutputDeltaNotification;
+use crate::protocol::ExecParams;
+use crate::protocol::ExecResponse;
+use crate::protocol::FS_COPY_METHOD;
+use crate::protocol::FS_CREATE_DIRECTORY_METHOD;
+use crate::protocol::FS_GET_METADATA_METHOD;
+use crate::protocol::FS_READ_DIRECTORY_METHOD;
+use crate::protocol::FS_READ_FILE_METHOD;
+use crate::protocol::FS_REMOVE_METHOD;
+use crate::protocol::FS_WRITE_FILE_METHOD;
+use crate::protocol::INITIALIZE_METHOD;
+use crate::protocol::INITIALIZED_METHOD;
+use crate::protocol::InitializeParams;
+use crate::protocol::InitializeResponse;
+use crate::protocol::ReadParams;
+use crate::protocol::ReadResponse;
+use crate::protocol::TerminateParams;
+use crate::protocol::TerminateResponse;
+use crate::protocol::WriteParams;
+use crate::protocol::WriteResponse;
+use codex_app_server_protocol::FsCopyParams;
+use codex_app_server_protocol::FsCopyResponse;
+use codex_app_server_protocol::FsCreateDirectoryParams;
+use codex_app_server_protocol::FsCreateDirectoryResponse;
+use codex_app_server_protocol::FsGetMetadataParams;
+use codex_app_server_protocol::FsGetMetadataResponse;
+use codex_app_server_protocol::FsReadDirectoryParams;
+use codex_app_server_protocol::FsReadDirectoryResponse;
+use codex_app_server_protocol::FsReadFileParams;
+use codex_app_server_protocol::FsReadFileResponse;
+use codex_app_server_protocol::FsRemoveParams;
+use codex_app_server_protocol::FsRemoveResponse;
+use codex_app_server_protocol::FsWriteFileParams;
+use codex_app_server_protocol::FsWriteFileResponse;
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub(crate) enum ExecServerInboundMessage {
+    Request(ExecServerRequest),
+    Notification(ExecServerClientNotification),
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub(crate) enum ExecServerRequest {
+    Initialize {
+        request_id: RequestId,
+        params: InitializeParams,
+    },
+    Exec {
+        request_id: RequestId,
+        params: ExecParams,
+    },
+    Read {
+        request_id: RequestId,
+        params: ReadParams,
+    },
+    Write {
+        request_id: RequestId,
+        params: WriteParams,
+    },
+    Terminate {
+        request_id: RequestId,
+        params: TerminateParams,
+    },
+    FsReadFile {
+        request_id: RequestId,
+        params: FsReadFileParams,
+    },
+    FsWriteFile {
+        request_id: RequestId,
+        params: FsWriteFileParams,
+    },
+    FsCreateDirectory {
+        request_id: RequestId,
+        params: FsCreateDirectoryParams,
+    },
+    FsGetMetadata {
+        request_id: RequestId,
+        params: FsGetMetadataParams,
+    },
+    FsReadDirectory {
+        request_id: RequestId,
+        params: FsReadDirectoryParams,
+    },
+    FsRemove {
+        request_id: RequestId,
+        params: FsRemoveParams,
+    },
+    FsCopy {
+        request_id: RequestId,
+        params: FsCopyParams,
+    },
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub(crate) enum ExecServerClientNotification {
+    Initialized,
+}
+
+#[derive(Debug, Clone, PartialEq)]
+pub(crate) enum ExecServerOutboundMessage {
+    Response {
+        request_id: RequestId,
+        response: ExecServerResponseMessage,
+    },
+    Error {
+        request_id: RequestId,
+        error: JSONRPCErrorError,
+    },
+    Notification(ExecServerServerNotification),
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub(crate) enum ExecServerResponseMessage {
+    Initialize(InitializeResponse),
+    Exec(ExecResponse),
+    Read(ReadResponse),
+    Write(WriteResponse),
+    Terminate(TerminateResponse),
+    FsReadFile(FsReadFileResponse),
+    FsWriteFile(FsWriteFileResponse),
+    FsCreateDirectory(FsCreateDirectoryResponse),
+    FsGetMetadata(FsGetMetadataResponse),
+    FsReadDirectory(FsReadDirectoryResponse),
+    FsRemove(FsRemoveResponse),
+    FsCopy(FsCopyResponse),
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub(crate) enum ExecServerServerNotification {
+    OutputDelta(ExecOutputDeltaNotification),
+    Exited(ExecExitedNotification),
+}
+
+#[derive(Debug, Clone, PartialEq)]
+pub(crate) enum RoutedExecServerMessage {
+    Inbound(ExecServerInboundMessage),
+    ImmediateOutbound(ExecServerOutboundMessage),
+}
+
+pub(crate) fn route_jsonrpc_message(
+    message: JSONRPCMessage,
+) -> Result<RoutedExecServerMessage, String> {
+    match message {
+        JSONRPCMessage::Request(request) => route_request(request),
+        JSONRPCMessage::Notification(notification) => route_notification(notification),
+        JSONRPCMessage::Response(response) => Err(format!(
+            "unexpected client response for request id {:?}",
+            response.id
+        )),
+        JSONRPCMessage::Error(error) => Err(format!(
+            "unexpected client error for request id {:?}",
+            error.id
+        )),
+    }
+}
+
+pub(crate) fn encode_outbound_message(
+    message: ExecServerOutboundMessage,
+) -> Result<JSONRPCMessage, serde_json::Error> {
+    match message {
+        ExecServerOutboundMessage::Response {
+            request_id,
+            response,
+        } => Ok(JSONRPCMessage::Response(JSONRPCResponse {
+            id: request_id,
+            result: serialize_response(response)?,
+        })),
+        ExecServerOutboundMessage::Error { request_id, error } => {
+            Ok(JSONRPCMessage::Error(JSONRPCError {
+                id: request_id,
+                error,
+            }))
+        }
+        ExecServerOutboundMessage::Notification(notification) => Ok(JSONRPCMessage::Notification(
+            serialize_notification(notification)?,
+        )),
+    }
+}
+
+pub(crate) fn invalid_request(message: String) -> JSONRPCErrorError {
+    JSONRPCErrorError {
+        code: -32600,
+        data: None,
+        message,
+    }
+}
+
+pub(crate) fn invalid_params(message: String) -> JSONRPCErrorError {
+    JSONRPCErrorError {
+        code: -32602,
+        data: None,
+        message,
+    }
+}
+
+pub(crate) fn internal_error(message: String) -> JSONRPCErrorError {
+    JSONRPCErrorError {
+        code: -32603,
+        data: None,
+        message,
+    }
+}
+
+fn route_request(request: JSONRPCRequest) -> Result<RoutedExecServerMessage, String> {
+    match request.method.as_str() {
+        INITIALIZE_METHOD => Ok(parse_request_params(request, |request_id, params| {
+            ExecServerRequest::Initialize { request_id, params }
+        })),
+        EXEC_METHOD => Ok(parse_request_params(request, |request_id, params| {
+            ExecServerRequest::Exec { request_id, params }
+        })),
+        EXEC_READ_METHOD => Ok(parse_request_params(request, |request_id, params| {
+            ExecServerRequest::Read { request_id, params }
+        })),
+        EXEC_WRITE_METHOD => Ok(parse_request_params(request, |request_id, params| {
+            ExecServerRequest::Write { request_id, params }
+        })),
+        EXEC_TERMINATE_METHOD => Ok(parse_request_params(request, |request_id, params| {
+            ExecServerRequest::Terminate { request_id, params }
+        })),
+        FS_READ_FILE_METHOD => Ok(parse_request_params(request, |request_id, params| {
+            ExecServerRequest::FsReadFile { request_id, params }
+        })),
+        FS_WRITE_FILE_METHOD => Ok(parse_request_params(request, |request_id, params| {
+            ExecServerRequest::FsWriteFile { request_id, params }
+        })),
+        FS_CREATE_DIRECTORY_METHOD => Ok(parse_request_params(request, |request_id, params| {
+            ExecServerRequest::FsCreateDirectory { request_id, params }
+        })),
+        FS_GET_METADATA_METHOD => Ok(parse_request_params(request, |request_id, params| {
+            ExecServerRequest::FsGetMetadata { request_id, params }
+        })),
+        FS_READ_DIRECTORY_METHOD => Ok(parse_request_params(request, |request_id, params| {
+            ExecServerRequest::FsReadDirectory { request_id, params }
+        })),
+        FS_REMOVE_METHOD => Ok(parse_request_params(request, |request_id, params| {
+            ExecServerRequest::FsRemove { request_id, params }
+        })),
+        FS_COPY_METHOD => Ok(parse_request_params(request, |request_id, params| {
+            ExecServerRequest::FsCopy { request_id, params }
+        })),
+        other => Ok(RoutedExecServerMessage::ImmediateOutbound(
+            ExecServerOutboundMessage::Error {
+                request_id: request.id,
+                error: invalid_request(format!("unknown method: {other}")),
+            },
+        )),
+    }
+}
+
+fn route_notification(
+    notification: JSONRPCNotification,
+) -> Result<RoutedExecServerMessage, String> {
+    match notification.method.as_str() {
+        INITIALIZED_METHOD => Ok(RoutedExecServerMessage::Inbound(
+            ExecServerInboundMessage::Notification(ExecServerClientNotification::Initialized),
+        )),
+        other => Err(format!("unexpected notification method: {other}")),
+    }
+}
+
+fn parse_request_params<P, F>(request: JSONRPCRequest, build: F) -> RoutedExecServerMessage
+where
+    P: DeserializeOwned,
+    F: FnOnce(RequestId, P) -> ExecServerRequest,
+{
+    let request_id = request.id;
+    match serde_json::from_value::<P>(request.params.unwrap_or(serde_json::Value::Null)) {
+        Ok(params) => RoutedExecServerMessage::Inbound(ExecServerInboundMessage::Request(build(
+            request_id, params,
+        ))),
+        Err(err) => RoutedExecServerMessage::ImmediateOutbound(ExecServerOutboundMessage::Error {
+            request_id,
+            error: invalid_params(err.to_string()),
+        }),
+    }
+}
+
+fn serialize_response(
+    response: ExecServerResponseMessage,
+) -> Result<serde_json::Value, serde_json::Error> {
+    match response {
+        ExecServerResponseMessage::Initialize(response) => serde_json::to_value(response),
+        ExecServerResponseMessage::Exec(response) => serde_json::to_value(response),
+        ExecServerResponseMessage::Read(response) => serde_json::to_value(response),
+        ExecServerResponseMessage::Write(response) => serde_json::to_value(response),
+        ExecServerResponseMessage::Terminate(response) => serde_json::to_value(response),
+        ExecServerResponseMessage::FsReadFile(response) => serde_json::to_value(response),
+        ExecServerResponseMessage::FsWriteFile(response) => serde_json::to_value(response),
+        ExecServerResponseMessage::FsCreateDirectory(response) => serde_json::to_value(response),
+        ExecServerResponseMessage::FsGetMetadata(response) => serde_json::to_value(response),
+        ExecServerResponseMessage::FsReadDirectory(response) => serde_json::to_value(response),
+        ExecServerResponseMessage::FsRemove(response) => serde_json::to_value(response),
+        ExecServerResponseMessage::FsCopy(response) => serde_json::to_value(response),
+    }
+}
+
+fn serialize_notification(
+    notification: ExecServerServerNotification,
+) -> Result<JSONRPCNotification, serde_json::Error> {
+    match notification {
+        ExecServerServerNotification::OutputDelta(params) => Ok(JSONRPCNotification {
+            method: EXEC_OUTPUT_DELTA_METHOD.to_string(),
+            params: Some(serde_json::to_value(params)?),
+        }),
+        ExecServerServerNotification::Exited(params) => Ok(JSONRPCNotification {
+            method: EXEC_EXITED_METHOD.to_string(),
+            params: Some(serde_json::to_value(params)?),
+        }),
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use pretty_assertions::assert_eq;
+    use serde_json::json;
+
+    use super::ExecServerClientNotification;
+    use super::ExecServerInboundMessage;
+    use super::ExecServerOutboundMessage;
+    use super::ExecServerRequest;
+    use super::ExecServerResponseMessage;
+    use super::ExecServerServerNotification;
+    use super::RoutedExecServerMessage;
+    use super::encode_outbound_message;
+    use super::route_jsonrpc_message;
+    use crate::protocol::EXEC_EXITED_METHOD;
+    use crate::protocol::EXEC_METHOD;
+    use crate::protocol::ExecExitedNotification;
+    use crate::protocol::ExecParams;
+    use crate::protocol::ExecResponse;
+    use crate::protocol::ExecSandboxConfig;
+    use crate::protocol::ExecSandboxMode;
+    use crate::protocol::INITIALIZE_METHOD;
+    use crate::protocol::INITIALIZED_METHOD;
+    use crate::protocol::InitializeParams;
+    use codex_app_server_protocol::JSONRPCMessage;
+    use codex_app_server_protocol::JSONRPCNotification;
+    use codex_app_server_protocol::JSONRPCRequest;
+    use codex_app_server_protocol::JSONRPCResponse;
+    use codex_app_server_protocol::RequestId;
+
+    #[test]
+    fn routes_initialize_requests_to_typed_variants() {
+        let routed = route_jsonrpc_message(JSONRPCMessage::Request(JSONRPCRequest {
+            id: RequestId::Integer(1),
+            method: INITIALIZE_METHOD.to_string(),
+            params: Some(json!({ "clientName": "test-client" })),
+            trace: None,
+        }))
+        .expect("initialize request should route");
+
+        assert_eq!(
+            routed,
+            RoutedExecServerMessage::Inbound(ExecServerInboundMessage::Request(
+                ExecServerRequest::Initialize {
+                    request_id: RequestId::Integer(1),
+                    params: InitializeParams {
+                        client_name: "test-client".to_string(),
+                    },
+                },
+            ))
+        );
+    }
+
+    #[test]
+    fn malformed_exec_params_return_immediate_error_outbound() {
+        let routed = route_jsonrpc_message(JSONRPCMessage::Request(JSONRPCRequest {
+            id: RequestId::Integer(2),
+            method: EXEC_METHOD.to_string(),
+            params: Some(json!({ "processId": "proc-1" })),
+            trace: None,
+        }))
+        .expect("exec request should route");
+
+        let RoutedExecServerMessage::ImmediateOutbound(ExecServerOutboundMessage::Error {
+            request_id,
+            error,
+        }) = routed
+        else {
+            panic!("expected invalid-params error outbound");
+        };
+        assert_eq!(request_id, RequestId::Integer(2));
+        assert_eq!(error.code, -32602);
+    }
+
+    #[test]
+    fn routes_initialized_notifications_to_typed_variants() {
+        let routed = route_jsonrpc_message(JSONRPCMessage::Notification(JSONRPCNotification {
+            method: INITIALIZED_METHOD.to_string(),
+            params: Some(json!({})),
+        }))
+        .expect("initialized notification should route");
+
+        assert_eq!(
+            routed,
+            RoutedExecServerMessage::Inbound(ExecServerInboundMessage::Notification(
+                ExecServerClientNotification::Initialized,
+            ))
+        );
+    }
+
+    #[test]
+    fn serializes_typed_notifications_back_to_jsonrpc() {
+        let message = encode_outbound_message(ExecServerOutboundMessage::Notification(
+            ExecServerServerNotification::Exited(ExecExitedNotification {
+                process_id: "proc-1".to_string(),
+                exit_code: 0,
+            }),
+        ))
+        .expect("notification should serialize");
+
+        assert_eq!(
+            message,
+            JSONRPCMessage::Notification(JSONRPCNotification {
+                method: EXEC_EXITED_METHOD.to_string(),
+                params: Some(json!({
+                    "processId": "proc-1",
+                    "exitCode": 0,
+                })),
+            })
+        );
+    }
+
+    #[test]
+    fn serializes_typed_responses_back_to_jsonrpc() {
+        let message = encode_outbound_message(ExecServerOutboundMessage::Response {
+            request_id: RequestId::Integer(3),
+            response: ExecServerResponseMessage::Exec(ExecResponse {
+                process_id: "proc-1".to_string(),
+            }),
+        })
+        .expect("response should serialize");
+
+        assert_eq!(
+            message,
+            JSONRPCMessage::Response(codex_app_server_protocol::JSONRPCResponse {
+                id: RequestId::Integer(3),
+                result: json!({
+                    "processId": "proc-1",
+                }),
+            })
+        );
+    }
+
+    #[test]
+    fn routes_exec_requests_with_typed_params() {
+        let cwd = std::env::current_dir().expect("cwd");
+        let routed = route_jsonrpc_message(JSONRPCMessage::Request(JSONRPCRequest {
+            id: RequestId::Integer(4),
+            method: EXEC_METHOD.to_string(),
+            params: Some(json!({
+                "processId": "proc-1",
+                "argv": ["bash", "-lc", "true"],
+                "cwd": cwd,
+                "env": {},
+                "tty": true,
+                "arg0": null,
+            })),
+            trace: None,
+        }))
+        .expect("exec request should route");
+
+        let RoutedExecServerMessage::Inbound(ExecServerInboundMessage::Request(
+            ExecServerRequest::Exec { request_id, params },
+        )) = routed
+        else {
+            panic!("expected typed exec request");
+        };
+        assert_eq!(request_id, RequestId::Integer(4));
+        assert_eq!(
+            params,
+            ExecParams {
+                process_id: "proc-1".to_string(),
+                argv: vec!["bash".to_string(), "-lc".to_string(), "true".to_string()],
+                cwd: std::env::current_dir().expect("cwd"),
+                env: std::collections::HashMap::new(),
+                tty: true,
+                arg0: None,
+                sandbox: None,
+            }
+        );
+    }
+
+    #[test]
+    fn routes_exec_requests_with_optional_sandbox_config() {
+        let cwd = std::env::current_dir().expect("cwd");
+        let routed = route_jsonrpc_message(JSONRPCMessage::Request(JSONRPCRequest {
+            id: RequestId::Integer(4),
+            method: EXEC_METHOD.to_string(),
+            params: Some(json!({
+                "processId": "proc-1",
+                "argv": ["bash", "-lc", "true"],
+                "cwd": cwd,
+                "env": {},
+                "tty": true,
+                "arg0": null,
+                "sandbox": {
+                    "mode": "none",
+                },
+            })),
+            trace: None,
+        }))
+        .expect("exec request with sandbox should route");
+
+        let RoutedExecServerMessage::Inbound(ExecServerInboundMessage::Request(
+            ExecServerRequest::Exec { request_id, params },
+        )) = routed
+        else {
+            panic!("expected typed exec request");
+        };
+        assert_eq!(request_id, RequestId::Integer(4));
+        assert_eq!(
+            params,
+            ExecParams {
+                process_id: "proc-1".to_string(),
+                argv: vec!["bash".to_string(), "-lc".to_string(), "true".to_string()],
+                cwd: std::env::current_dir().expect("cwd"),
+                env: std::collections::HashMap::new(),
+                tty: true,
+                arg0: None,
+                sandbox: Some(ExecSandboxConfig {
+                    mode: ExecSandboxMode::None,
+                }),
+            }
+        );
+    }
+
+    #[test]
+    fn unknown_request_methods_return_immediate_invalid_request_errors() {
+        let routed = route_jsonrpc_message(JSONRPCMessage::Request(JSONRPCRequest {
+            id: RequestId::Integer(5),
+            method: "process/unknown".to_string(),
+            params: Some(json!({})),
+            trace: None,
+        }))
+        .expect("unknown request should still route");
+
+        assert_eq!(
+            routed,
+            RoutedExecServerMessage::ImmediateOutbound(ExecServerOutboundMessage::Error {
+                request_id: RequestId::Integer(5),
+                error: super::invalid_request("unknown method: process/unknown".to_string()),
+            })
+        );
+    }
+
+    #[test]
+    fn unexpected_client_notifications_are_rejected() {
+        let err = route_jsonrpc_message(JSONRPCMessage::Notification(JSONRPCNotification {
+            method: "process/output".to_string(),
+            params: Some(json!({})),
+        }))
+        .expect_err("unexpected client notification should fail");
+
+        assert_eq!(err, "unexpected notification method: process/output");
+    }
+
+    #[test]
+    fn unexpected_client_responses_are_rejected() {
+        let err = route_jsonrpc_message(JSONRPCMessage::Response(JSONRPCResponse {
+            id: RequestId::Integer(6),
+            result: json!({}),
+        }))
+        .expect_err("unexpected client response should fail");
+
+        assert_eq!(err, "unexpected client response for request id Integer(6)");
+    }
+}

codex-rs/exec-server/src/server/transport.rs

@@ -0,0 +1,166 @@
+use std::net::SocketAddr;
+use std::str::FromStr;
+
+use tokio::net::TcpListener;
+use tokio_tungstenite::accept_async;
+use tracing::warn;
+
+use crate::connection::JsonRpcConnection;
+use crate::server::processor::run_connection;
+
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub enum ExecServerTransport {
+    Stdio,
+    WebSocket { bind_address: SocketAddr },
+}
+
+#[derive(Debug, Clone, Eq, PartialEq)]
+pub enum ExecServerTransportParseError {
+    UnsupportedListenUrl(String),
+    InvalidWebSocketListenUrl(String),
+}
+
+impl std::fmt::Display for ExecServerTransportParseError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            ExecServerTransportParseError::UnsupportedListenUrl(listen_url) => write!(
+                f,
+                "unsupported --listen URL `{listen_url}`; expected `stdio://` or `ws://IP:PORT`"
+            ),
+            ExecServerTransportParseError::InvalidWebSocketListenUrl(listen_url) => write!(
+                f,
+                "invalid websocket --listen URL `{listen_url}`; expected `ws://IP:PORT`"
+            ),
+        }
+    }
+}
+
+impl std::error::Error for ExecServerTransportParseError {}
+
+impl ExecServerTransport {
+    pub const DEFAULT_LISTEN_URL: &str = "stdio://";
+
+    pub fn from_listen_url(listen_url: &str) -> Result<Self, ExecServerTransportParseError> {
+        if listen_url == Self::DEFAULT_LISTEN_URL {
+            return Ok(Self::Stdio);
+        }
+
+        if let Some(socket_addr) = listen_url.strip_prefix("ws://") {
+            let bind_address = socket_addr.parse::<SocketAddr>().map_err(|_| {
+                ExecServerTransportParseError::InvalidWebSocketListenUrl(listen_url.to_string())
+            })?;
+            return Ok(Self::WebSocket { bind_address });
+        }
+
+        Err(ExecServerTransportParseError::UnsupportedListenUrl(
+            listen_url.to_string(),
+        ))
+    }
+}
+
+impl FromStr for ExecServerTransport {
+    type Err = ExecServerTransportParseError;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        Self::from_listen_url(s)
+    }
+}
+
+pub(crate) async fn run_transport(
+    transport: ExecServerTransport,
+) -> Result<(), Box<dyn std::error::Error + Send + Sync>> {
+    match transport {
+        ExecServerTransport::Stdio => {
+            run_connection(JsonRpcConnection::from_stdio(
+                tokio::io::stdin(),
+                tokio::io::stdout(),
+                "exec-server stdio".to_string(),
+            ))
+            .await;
+            Ok(())
+        }
+        ExecServerTransport::WebSocket { bind_address } => {
+            run_websocket_listener(bind_address).await
+        }
+    }
+}
+
+async fn run_websocket_listener(
+    bind_address: SocketAddr,
+) -> Result<(), Box<dyn std::error::Error + Send + Sync>> {
+    let listener = TcpListener::bind(bind_address).await?;
+    let local_addr = listener.local_addr()?;
+    print_websocket_startup_banner(local_addr);
+
+    loop {
+        let (stream, peer_addr) = listener.accept().await?;
+        tokio::spawn(async move {
+            match accept_async(stream).await {
+                Ok(websocket) => {
+                    run_connection(JsonRpcConnection::from_websocket(
+                        websocket,
+                        format!("exec-server websocket {peer_addr}"),
+                    ))
+                    .await;
+                }
+                Err(err) => {
+                    warn!(
+                        "failed to accept exec-server websocket connection from {peer_addr}: {err}"
+                    );
+                }
+            }
+        });
+    }
+}
+
+#[allow(clippy::print_stderr)]
+fn print_websocket_startup_banner(addr: SocketAddr) {
+    eprintln!("codex-exec-server listening on ws://{addr}");
+}
+
+#[cfg(test)]
+mod tests {
+    use pretty_assertions::assert_eq;
+
+    use super::ExecServerTransport;
+
+    #[test]
+    fn exec_server_transport_parses_stdio_listen_url() {
+        let transport =
+            ExecServerTransport::from_listen_url(ExecServerTransport::DEFAULT_LISTEN_URL)
+                .expect("stdio listen URL should parse");
+        assert_eq!(transport, ExecServerTransport::Stdio);
+    }
+
+    #[test]
+    fn exec_server_transport_parses_websocket_listen_url() {
+        let transport = ExecServerTransport::from_listen_url("ws://127.0.0.1:1234")
+            .expect("websocket listen URL should parse");
+        assert_eq!(
+            transport,
+            ExecServerTransport::WebSocket {
+                bind_address: "127.0.0.1:1234".parse().expect("valid socket address"),
+            }
+        );
+    }
+
+    #[test]
+    fn exec_server_transport_rejects_invalid_websocket_listen_url() {
+        let err = ExecServerTransport::from_listen_url("ws://localhost:1234")
+            .expect_err("hostname bind address should be rejected");
+        assert_eq!(
+            err.to_string(),
+            "invalid websocket --listen URL `ws://localhost:1234`; expected `ws://IP:PORT`"
+        );
+    }
+
+    #[test]
+    fn exec_server_transport_rejects_unsupported_listen_url() {
+        let err = ExecServerTransport::from_listen_url("http://127.0.0.1:1234")
+            .expect_err("unsupported scheme should fail");
+        assert_eq!(
+            err.to_string(),
+            "unsupported --listen URL `http://127.0.0.1:1234`; expected `stdio://` or `ws://IP:PORT`"
+        );
+    }
+}

codex-rs/exec-server/tests/stdio_smoke.rs

@@ -0,0 +1,462 @@
+#![cfg(unix)]
+
+use std::process::Stdio;
+use std::time::Duration;
+
+use anyhow::Context;
+use codex_app_server_protocol::JSONRPCMessage;
+use codex_app_server_protocol::JSONRPCNotification;
+use codex_app_server_protocol::JSONRPCRequest;
+use codex_app_server_protocol::JSONRPCResponse;
+use codex_app_server_protocol::RequestId;
+use codex_exec_server::ExecOutputStream;
+use codex_exec_server::ExecParams;
+use codex_exec_server::ExecServerClient;
+use codex_exec_server::ExecServerClientConnectOptions;
+use codex_exec_server::ExecServerEvent;
+use codex_exec_server::ExecServerLaunchCommand;
+use codex_exec_server::InitializeParams;
+use codex_exec_server::InitializeResponse;
+use codex_exec_server::RemoteExecServerConnectArgs;
+use codex_exec_server::spawn_local_exec_server;
+use codex_utils_cargo_bin::cargo_bin;
+use pretty_assertions::assert_eq;
+use tokio::io::AsyncBufReadExt;
+use tokio::io::AsyncWriteExt;
+use tokio::io::BufReader;
+use tokio::process::Command;
+use tokio::sync::broadcast;
+use tokio::time::timeout;
+
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn exec_server_accepts_initialize_over_stdio() -> anyhow::Result<()> {
+    let binary = cargo_bin("codex-exec-server")?;
+    let mut child = Command::new(binary);
+    child.stdin(Stdio::piped());
+    child.stdout(Stdio::piped());
+    child.stderr(Stdio::inherit());
+    let mut child = child.spawn()?;
+
+    let mut stdin = child.stdin.take().expect("stdin");
+    let stdout = child.stdout.take().expect("stdout");
+    let mut stdout = BufReader::new(stdout).lines();
+
+    let initialize = JSONRPCMessage::Request(JSONRPCRequest {
+        id: RequestId::Integer(1),
+        method: "initialize".to_string(),
+        params: Some(serde_json::to_value(InitializeParams {
+            client_name: "exec-server-test".to_string(),
+        })?),
+        trace: None,
+    });
+    stdin
+        .write_all(format!("{}\n", serde_json::to_string(&initialize)?).as_bytes())
+        .await?;
+
+    let response_line = timeout(Duration::from_secs(5), stdout.next_line()).await??;
+    let response_line = response_line.expect("response line");
+    let response: JSONRPCMessage = serde_json::from_str(&response_line)?;
+    let JSONRPCMessage::Response(JSONRPCResponse { id, result }) = response else {
+        panic!("expected initialize response");
+    };
+    assert_eq!(id, RequestId::Integer(1));
+    let initialize_response: InitializeResponse = serde_json::from_value(result)?;
+    assert_eq!(initialize_response.protocol_version, "exec-server.v0");
+
+    let initialized = JSONRPCMessage::Notification(JSONRPCNotification {
+        method: "initialized".to_string(),
+        params: Some(serde_json::json!({})),
+    });
+    stdin
+        .write_all(format!("{}\n", serde_json::to_string(&initialized)?).as_bytes())
+        .await?;
+
+    child.start_kill()?;
+    Ok(())
+}
+
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn exec_server_accepts_explicit_none_sandbox_over_stdio() -> anyhow::Result<()> {
+    let binary = cargo_bin("codex-exec-server")?;
+    let mut child = Command::new(binary);
+    child.stdin(Stdio::piped());
+    child.stdout(Stdio::piped());
+    child.stderr(Stdio::inherit());
+    let mut child = child.spawn()?;
+
+    let mut stdin = child.stdin.take().expect("stdin");
+    let stdout = child.stdout.take().expect("stdout");
+    let mut stdout = BufReader::new(stdout).lines();
+
+    send_initialize_over_stdio(&mut stdin, &mut stdout).await?;
+
+    let exec = JSONRPCMessage::Request(JSONRPCRequest {
+        id: RequestId::Integer(2),
+        method: "process/start".to_string(),
+        params: Some(serde_json::json!({
+            "processId": "proc-1",
+            "argv": ["printf", "sandbox-none"],
+            "cwd": std::env::current_dir()?,
+            "env": {},
+            "tty": false,
+            "arg0": null,
+            "sandbox": {
+                "mode": "none"
+            }
+        })),
+        trace: None,
+    });
+    stdin
+        .write_all(format!("{}\n", serde_json::to_string(&exec)?).as_bytes())
+        .await?;
+
+    let response_line = timeout(Duration::from_secs(5), stdout.next_line()).await??;
+    let response_line = response_line.expect("exec response line");
+    let response: JSONRPCMessage = serde_json::from_str(&response_line)?;
+    let JSONRPCMessage::Response(JSONRPCResponse { id, result }) = response else {
+        panic!("expected process/start response");
+    };
+    assert_eq!(id, RequestId::Integer(2));
+    assert_eq!(result, serde_json::json!({ "processId": "proc-1" }));
+
+    let deadline = tokio::time::Instant::now() + Duration::from_secs(5);
+    let mut saw_output = false;
+    while !saw_output {
+        let remaining = deadline.saturating_duration_since(tokio::time::Instant::now());
+        let line = timeout(remaining, stdout.next_line()).await??;
+        let line = line.context("missing process notification")?;
+        let message: JSONRPCMessage = serde_json::from_str(&line)?;
+        if let JSONRPCMessage::Notification(JSONRPCNotification { method, params }) = message
+            && method == "process/output"
+        {
+            let params = params.context("missing process/output params")?;
+            assert_eq!(params["processId"], "proc-1");
+            assert_eq!(params["stream"], "stdout");
+            assert_eq!(params["chunk"], "c2FuZGJveC1ub25l");
+            saw_output = true;
+        }
+    }
+
+    child.start_kill()?;
+    Ok(())
+}
+
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn exec_server_rejects_host_default_sandbox_over_stdio() -> anyhow::Result<()> {
+    let binary = cargo_bin("codex-exec-server")?;
+    let mut child = Command::new(binary);
+    child.stdin(Stdio::piped());
+    child.stdout(Stdio::piped());
+    child.stderr(Stdio::inherit());
+    let mut child = child.spawn()?;
+
+    let mut stdin = child.stdin.take().expect("stdin");
+    let stdout = child.stdout.take().expect("stdout");
+    let mut stdout = BufReader::new(stdout).lines();
+
+    send_initialize_over_stdio(&mut stdin, &mut stdout).await?;
+
+    let exec = JSONRPCMessage::Request(JSONRPCRequest {
+        id: RequestId::Integer(2),
+        method: "process/start".to_string(),
+        params: Some(serde_json::json!({
+            "processId": "proc-1",
+            "argv": ["bash", "-lc", "true"],
+            "cwd": std::env::current_dir()?,
+            "env": {},
+            "tty": false,
+            "arg0": null,
+            "sandbox": {
+                "mode": "hostDefault"
+            }
+        })),
+        trace: None,
+    });
+    stdin
+        .write_all(format!("{}\n", serde_json::to_string(&exec)?).as_bytes())
+        .await?;
+
+    let response_line = timeout(Duration::from_secs(5), stdout.next_line()).await??;
+    let response_line = response_line.expect("exec error line");
+    let response: JSONRPCMessage = serde_json::from_str(&response_line)?;
+    let JSONRPCMessage::Error(codex_app_server_protocol::JSONRPCError { id, error }) = response
+    else {
+        panic!("expected process/start error");
+    };
+    assert_eq!(id, RequestId::Integer(2));
+    assert_eq!(error.code, -32600);
+    assert_eq!(
+        error.message,
+        "sandbox mode `hostDefault` is not supported by exec-server yet"
+    );
+
+    child.start_kill()?;
+    Ok(())
+}
+
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn exec_server_client_streams_output_and_accepts_writes() -> anyhow::Result<()> {
+    let mut env = std::collections::HashMap::new();
+    if let Some(path) = std::env::var_os("PATH") {
+        env.insert("PATH".to_string(), path.to_string_lossy().into_owned());
+    }
+
+    let server = spawn_local_exec_server(
+        ExecServerLaunchCommand {
+            program: cargo_bin("codex-exec-server")?,
+            args: Vec::new(),
+        },
+        ExecServerClientConnectOptions {
+            client_name: "exec-server-test".to_string(),
+            initialize_timeout: Duration::from_secs(5),
+        },
+    )
+    .await?;
+
+    let client = server.client();
+    let mut events = client.event_receiver();
+    let response = client
+        .exec(ExecParams {
+            process_id: "proc-1".to_string(),
+            argv: vec![
+                "bash".to_string(),
+                "-lc".to_string(),
+                "printf 'ready\\n'; while IFS= read -r line; do printf 'echo:%s\\n' \"$line\"; done"
+                    .to_string(),
+            ],
+            cwd: std::env::current_dir()?,
+            env,
+            tty: true,
+            arg0: None,
+            sandbox: None,
+        })
+        .await?;
+    let process_id = response.process_id;
+
+    let (stream, ready_output) = recv_until_contains(&mut events, &process_id, "ready").await?;
+    assert_eq!(stream, ExecOutputStream::Pty);
+    assert!(
+        ready_output.contains("ready"),
+        "expected initial ready output"
+    );
+
+    client.write(&process_id, b"hello\n".to_vec()).await?;
+
+    let (stream, echoed_output) =
+        recv_until_contains(&mut events, &process_id, "echo:hello").await?;
+    assert_eq!(stream, ExecOutputStream::Pty);
+    assert!(
+        echoed_output.contains("echo:hello"),
+        "expected echoed output"
+    );
+
+    client.terminate(&process_id).await?;
+    Ok(())
+}
+
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn exec_server_client_connects_over_websocket() -> anyhow::Result<()> {
+    let mut env = std::collections::HashMap::new();
+    if let Some(path) = std::env::var_os("PATH") {
+        env.insert("PATH".to_string(), path.to_string_lossy().into_owned());
+    }
+
+    let binary = cargo_bin("codex-exec-server")?;
+    let mut child = Command::new(binary);
+    child.args(["--listen", "ws://127.0.0.1:0"]);
+    child.stdin(Stdio::null());
+    child.stdout(Stdio::null());
+    child.stderr(Stdio::piped());
+    let mut child = child.spawn()?;
+    let stderr = child.stderr.take().expect("stderr");
+    let mut stderr_lines = BufReader::new(stderr).lines();
+    let websocket_url = read_websocket_url(&mut stderr_lines).await?;
+
+    let client = ExecServerClient::connect_websocket(RemoteExecServerConnectArgs {
+        websocket_url,
+        client_name: "exec-server-test".to_string(),
+        connect_timeout: Duration::from_secs(5),
+        initialize_timeout: Duration::from_secs(5),
+    })
+    .await?;
+
+    let mut events = client.event_receiver();
+    let response = client
+        .exec(ExecParams {
+            process_id: "proc-1".to_string(),
+            argv: vec![
+                "bash".to_string(),
+                "-lc".to_string(),
+                "printf 'ready\\n'; while IFS= read -r line; do printf 'echo:%s\\n' \"$line\"; done"
+                    .to_string(),
+            ],
+            cwd: std::env::current_dir()?,
+            env,
+            tty: true,
+            arg0: None,
+            sandbox: None,
+        })
+        .await?;
+    let process_id = response.process_id;
+
+    let (stream, ready_output) = recv_until_contains(&mut events, &process_id, "ready").await?;
+    assert_eq!(stream, ExecOutputStream::Pty);
+    assert!(
+        ready_output.contains("ready"),
+        "expected initial ready output"
+    );
+
+    client.write(&process_id, b"hello\n".to_vec()).await?;
+
+    let (stream, echoed_output) =
+        recv_until_contains(&mut events, &process_id, "echo:hello").await?;
+    assert_eq!(stream, ExecOutputStream::Pty);
+    assert!(
+        echoed_output.contains("echo:hello"),
+        "expected echoed output"
+    );
+
+    client.terminate(&process_id).await?;
+    child.start_kill()?;
+    Ok(())
+}
+
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn websocket_disconnect_terminates_processes_for_that_connection() -> anyhow::Result<()> {
+    let mut env = std::collections::HashMap::new();
+    if let Some(path) = std::env::var_os("PATH") {
+        env.insert("PATH".to_string(), path.to_string_lossy().into_owned());
+    }
+
+    let marker_path = std::env::temp_dir().join(format!(
+        "codex-exec-server-disconnect-{}-{}",
+        std::process::id(),
+        std::time::SystemTime::now()
+            .duration_since(std::time::UNIX_EPOCH)?
+            .as_nanos()
+    ));
+    let _ = std::fs::remove_file(&marker_path);
+
+    let binary = cargo_bin("codex-exec-server")?;
+    let mut child = Command::new(binary);
+    child.args(["--listen", "ws://127.0.0.1:0"]);
+    child.stdin(Stdio::null());
+    child.stdout(Stdio::null());
+    child.stderr(Stdio::piped());
+    let mut child = child.spawn()?;
+    let stderr = child.stderr.take().expect("stderr");
+    let mut stderr_lines = BufReader::new(stderr).lines();
+    let websocket_url = read_websocket_url(&mut stderr_lines).await?;
+
+    {
+        let client = ExecServerClient::connect_websocket(RemoteExecServerConnectArgs {
+            websocket_url,
+            client_name: "exec-server-test".to_string(),
+            connect_timeout: Duration::from_secs(5),
+            initialize_timeout: Duration::from_secs(5),
+        })
+        .await?;
+
+        let _response = client
+            .exec(ExecParams {
+                process_id: "proc-1".to_string(),
+                argv: vec![
+                    "bash".to_string(),
+                    "-lc".to_string(),
+                    format!("sleep 2; printf disconnected > {}", marker_path.display()),
+                ],
+                cwd: std::env::current_dir()?,
+                env,
+                tty: false,
+                arg0: None,
+                sandbox: None,
+            })
+            .await?;
+    }
+
+    tokio::time::sleep(Duration::from_secs(3)).await;
+    assert!(
+        !marker_path.exists(),
+        "managed process should be terminated when the websocket client disconnects"
+    );
+
+    child.start_kill()?;
+    let _ = std::fs::remove_file(&marker_path);
+    Ok(())
+}
+
+async fn read_websocket_url<R>(lines: &mut tokio::io::Lines<BufReader<R>>) -> anyhow::Result<String>
+where
+    R: tokio::io::AsyncRead + Unpin,
+{
+    let line = timeout(Duration::from_secs(5), lines.next_line()).await??;
+    let line = line.context("missing websocket startup banner")?;
+    let websocket_url = line
+        .split_whitespace()
+        .find(|part| part.starts_with("ws://"))
+        .context("missing websocket URL in startup banner")?;
+    Ok(websocket_url.to_string())
+}
+
+async fn send_initialize_over_stdio<W, R>(
+    stdin: &mut W,
+    stdout: &mut tokio::io::Lines<BufReader<R>>,
+) -> anyhow::Result<()>
+where
+    W: tokio::io::AsyncWrite + Unpin,
+    R: tokio::io::AsyncRead + Unpin,
+{
+    let initialize = JSONRPCMessage::Request(JSONRPCRequest {
+        id: RequestId::Integer(1),
+        method: "initialize".to_string(),
+        params: Some(serde_json::to_value(InitializeParams {
+            client_name: "exec-server-test".to_string(),
+        })?),
+        trace: None,
+    });
+    stdin
+        .write_all(format!("{}\n", serde_json::to_string(&initialize)?).as_bytes())
+        .await?;
+
+    let response_line = timeout(Duration::from_secs(5), stdout.next_line()).await??;
+    let response_line = response_line
+        .ok_or_else(|| anyhow::anyhow!("missing initialize response line from stdio server"))?;
+    let response: JSONRPCMessage = serde_json::from_str(&response_line)?;
+    let JSONRPCMessage::Response(JSONRPCResponse { id, result }) = response else {
+        panic!("expected initialize response");
+    };
+    assert_eq!(id, RequestId::Integer(1));
+    let initialize_response: InitializeResponse = serde_json::from_value(result)?;
+    assert_eq!(initialize_response.protocol_version, "exec-server.v0");
+
+    let initialized = JSONRPCMessage::Notification(JSONRPCNotification {
+        method: "initialized".to_string(),
+        params: Some(serde_json::json!({})),
+    });
+    stdin
+        .write_all(format!("{}\n", serde_json::to_string(&initialized)?).as_bytes())
+        .await?;
+
+    Ok(())
+}
+
+async fn recv_until_contains(
+    events: &mut broadcast::Receiver<ExecServerEvent>,
+    process_id: &str,
+    needle: &str,
+) -> anyhow::Result<(ExecOutputStream, String)> {
+    let deadline = tokio::time::Instant::now() + Duration::from_secs(5);
+    let mut collected = String::new();
+    loop {
+        let remaining = deadline.saturating_duration_since(tokio::time::Instant::now());
+        let event = timeout(remaining, events.recv()).await??;
+        if let ExecServerEvent::OutputDelta(output_event) = event
+            && output_event.process_id == process_id
+        {
+            collected.push_str(&String::from_utf8_lossy(&output_event.chunk.into_inner()));
+            if collected.contains(needle) {
+                return Ok((output_event.stream, collected));
+            }
+        }
+    }
+}

codex-rs/exec/tests/suite/mod.rs

@@ -6,6 +6,7 @@ mod ephemeral;
 mod mcp_required_exit;
 mod originator;
 mod output_schema;
+mod remote_exec_server;
 mod resume;
 mod sandbox;
 mod server_error_exit;

codex-rs/exec/tests/suite/remote_exec_server.rs

@@ -0,0 +1,90 @@
+#![cfg(not(target_os = "windows"))]
+#![allow(clippy::expect_used, clippy::unwrap_used)]
+
+use std::net::TcpListener;
+use std::process::Stdio;
+use std::time::Duration;
+
+use core_test_support::responses;
+use core_test_support::test_codex_exec::test_codex_exec;
+use pretty_assertions::assert_eq;
+use serde_json::json;
+use tokio::process::Command;
+
+#[tokio::test(flavor = "multi_thread", worker_threads = 4)]
+async fn exec_cli_can_route_exec_command_through_remote_exec_server() -> anyhow::Result<()> {
+    let test = test_codex_exec();
+
+    let websocket_listener = TcpListener::bind("127.0.0.1:0")?;
+    let websocket_port = websocket_listener.local_addr()?.port();
+    drop(websocket_listener);
+    let websocket_url = format!("ws://127.0.0.1:{websocket_port}");
+
+    let mut exec_server = Command::new(codex_utils_cargo_bin::cargo_bin("codex-exec-server")?)
+        .arg("--listen")
+        .arg(&websocket_url)
+        .stdin(Stdio::null())
+        .stdout(Stdio::null())
+        .stderr(Stdio::inherit())
+        .spawn()?;
+    tokio::time::sleep(Duration::from_millis(250)).await;
+
+    let generated_path = test.cwd_path().join("remote_exec_generated.txt");
+    let server = responses::start_mock_server().await;
+    let response_mock = responses::mount_sse_sequence(
+        &server,
+        vec![
+            responses::sse(vec![
+                responses::ev_response_created("resp-1"),
+                responses::ev_function_call(
+                    "call-exec",
+                    "exec_command",
+                    &serde_json::to_string(&json!({
+                        "cmd": "/bin/sh -lc 'printf from-remote > remote_exec_generated.txt'",
+                        "yield_time_ms": 500,
+                    }))?,
+                ),
+                responses::ev_completed("resp-1"),
+            ]),
+            responses::sse(vec![
+                responses::ev_response_created("resp-2"),
+                responses::ev_assistant_message("msg-1", "done"),
+                responses::ev_completed("resp-2"),
+            ]),
+        ],
+    )
+    .await;
+
+    test.cmd_with_server(&server)
+        .arg("--skip-git-repo-check")
+        .arg("-s")
+        .arg("danger-full-access")
+        .arg("-c")
+        .arg("experimental_use_unified_exec_tool=true")
+        .arg("-c")
+        .arg(format!(
+            "experimental_unified_exec_exec_server_websocket_url={}",
+            serde_json::to_string(&websocket_url)?
+        ))
+        .arg("-c")
+        .arg(format!(
+            "experimental_unified_exec_exec_server_workspace_root={}",
+            serde_json::to_string(test.cwd_path().to_string_lossy().as_ref())?
+        ))
+        .arg("run remote exec-server command")
+        .assert()
+        .success();
+
+    let deadline = tokio::time::Instant::now() + Duration::from_secs(5);
+    while tokio::time::Instant::now() < deadline && !generated_path.exists() {
+        tokio::time::sleep(Duration::from_millis(50)).await;
+    }
+    assert_eq!(std::fs::read_to_string(&generated_path)?, "from-remote");
+
+    let requests = response_mock.requests();
+    assert_eq!(requests.len(), 2);
+
+    exec_server.start_kill()?;
+    let _ = exec_server.wait().await;
+    Ok(())
+}

codex-rs/mcp-types/Cargo.toml

@@ -0,0 +1,17 @@
+[package]
+edition.workspace = true
+license.workspace = true
+name = "codex-mcp-types"
+version.workspace = true
+
+[lib]
+doctest = false
+name = "codex_mcp_types"
+path = "src/lib.rs"
+
+[lints]
+workspace = true
+
+[dependencies]
+codex-protocol = { workspace = true }
+serde = { workspace = true, features = ["derive"] }

codex-rs/mcp-types/src/lib.rs

@@ -0,0 +1,53 @@
+//! Small, stable MCP data helpers split out of `codex-core`.
+
+use std::collections::HashMap;
+use std::path::PathBuf;
+
+use codex_protocol::mcp::Tool;
+use codex_protocol::protocol::SandboxPolicy;
+use serde::Deserialize;
+use serde::Serialize;
+
+const MCP_TOOL_NAME_PREFIX: &str = "mcp";
+const MCP_TOOL_NAME_DELIMITER: &str = "__";
+
+/// State needed by MCP servers to align their own sandboxing decisions with Codex.
+#[derive(Debug, Clone, Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct SandboxState {
+    pub sandbox_policy: SandboxPolicy,
+    pub codex_linux_sandbox_exe: Option<PathBuf>,
+    pub sandbox_cwd: PathBuf,
+    #[serde(default)]
+    pub use_legacy_landlock: bool,
+}
+
+pub fn split_qualified_tool_name(qualified_name: &str) -> Option<(String, String)> {
+    let mut parts = qualified_name.split(MCP_TOOL_NAME_DELIMITER);
+    let prefix = parts.next()?;
+    if prefix != MCP_TOOL_NAME_PREFIX {
+        return None;
+    }
+    let server_name = parts.next()?;
+    let tool_name: String = parts.collect::<Vec<_>>().join(MCP_TOOL_NAME_DELIMITER);
+    if tool_name.is_empty() {
+        None
+    } else {
+        Some((server_name.to_string(), tool_name))
+    }
+}
+
+pub fn group_tools_by_server(
+    tools: &HashMap<String, Tool>,
+) -> HashMap<String, HashMap<String, Tool>> {
+    let mut grouped = HashMap::new();
+    for (qualified_name, tool) in tools {
+        if let Some((server_name, tool_name)) = split_qualified_tool_name(qualified_name) {
+            grouped
+                .entry(server_name)
+                .or_insert_with(HashMap::new)
+                .insert(tool_name, tool.clone());
+        }
+    }
+    grouped
+}

codex-rs/tool-spec/Cargo.toml

@@ -0,0 +1,17 @@
+[package]
+edition.workspace = true
+license.workspace = true
+name = "codex-tool-spec"
+version.workspace = true
+
+[lib]
+doctest = false
+name = "codex_tool_spec"
+path = "src/lib.rs"
+
+[lints]
+workspace = true
+
+[dependencies]
+serde = { workspace = true, features = ["derive"] }
+serde_json = { workspace = true }

codex-rs/tool-spec/src/lib.rs

@@ -0,0 +1,173 @@
+//! Shared tool-schema types split out of `codex-core` so schema-only churn can
+//! rebuild independently from the full tool registry/orchestration crate.
+
+use serde::Deserialize;
+use serde::Serialize;
+use serde_json::Value as JsonValue;
+use serde_json::json;
+use std::collections::BTreeMap;
+
+/// Generic JSON-Schema subset needed for our tool definitions.
+#[derive(Debug, Clone, Serialize, Deserialize, PartialEq)]
+#[serde(tag = "type", rename_all = "lowercase")]
+pub enum JsonSchema {
+    Boolean {
+        #[serde(skip_serializing_if = "Option::is_none")]
+        description: Option<String>,
+    },
+    String {
+        #[serde(skip_serializing_if = "Option::is_none")]
+        description: Option<String>,
+    },
+    /// MCP schema allows "number" | "integer" for Number.
+    #[serde(alias = "integer")]
+    Number {
+        #[serde(skip_serializing_if = "Option::is_none")]
+        description: Option<String>,
+    },
+    Array {
+        items: Box<JsonSchema>,
+
+        #[serde(skip_serializing_if = "Option::is_none")]
+        description: Option<String>,
+    },
+    Object {
+        properties: BTreeMap<String, JsonSchema>,
+        #[serde(skip_serializing_if = "Option::is_none")]
+        required: Option<Vec<String>>,
+        #[serde(
+            rename = "additionalProperties",
+            skip_serializing_if = "Option::is_none"
+        )]
+        additional_properties: Option<AdditionalProperties>,
+    },
+}
+
+/// Whether additional properties are allowed, and if so, any required schema.
+#[derive(Debug, Clone, Serialize, Deserialize, PartialEq)]
+#[serde(untagged)]
+pub enum AdditionalProperties {
+    Boolean(bool),
+    Schema(Box<JsonSchema>),
+}
+
+impl From<bool> for AdditionalProperties {
+    fn from(b: bool) -> Self {
+        Self::Boolean(b)
+    }
+}
+
+impl From<JsonSchema> for AdditionalProperties {
+    fn from(s: JsonSchema) -> Self {
+        Self::Schema(Box::new(s))
+    }
+}
+
+/// Parse a tool `input_schema` or return an error for invalid schema.
+pub fn parse_tool_input_schema(input_schema: &JsonValue) -> Result<JsonSchema, serde_json::Error> {
+    let mut input_schema = input_schema.clone();
+    sanitize_json_schema(&mut input_schema);
+    serde_json::from_value::<JsonSchema>(input_schema)
+}
+
+/// Sanitize a JSON Schema (as `serde_json::Value`) so it can fit our limited
+/// `JsonSchema` enum. This function:
+/// - Ensures every schema object has a "type". If missing, infers it from
+///   common keywords (`properties` => object, `items` => array, `enum`/`const`/`format` => string)
+///   and otherwise defaults to "string".
+/// - Fills required child fields (e.g. array items, object properties) with
+///   permissive defaults when absent.
+fn sanitize_json_schema(value: &mut JsonValue) {
+    match value {
+        JsonValue::Bool(_) => {
+            // JSON Schema boolean form: true/false. Coerce to an accept-all string.
+            *value = json!({ "type": "string" });
+        }
+        JsonValue::Array(arr) => {
+            for v in arr.iter_mut() {
+                sanitize_json_schema(v);
+            }
+        }
+        JsonValue::Object(map) => {
+            if let Some(props) = map.get_mut("properties")
+                && let Some(props_map) = props.as_object_mut()
+            {
+                for (_k, v) in props_map.iter_mut() {
+                    sanitize_json_schema(v);
+                }
+            }
+            if let Some(items) = map.get_mut("items") {
+                sanitize_json_schema(items);
+            }
+            for combiner in ["oneOf", "anyOf", "allOf", "prefixItems"] {
+                if let Some(v) = map.get_mut(combiner) {
+                    sanitize_json_schema(v);
+                }
+            }
+
+            let mut ty = map.get("type").and_then(|v| v.as_str()).map(str::to_string);
+
+            if ty.is_none()
+                && let Some(JsonValue::Array(types)) = map.get("type")
+            {
+                for t in types {
+                    if let Some(tt) = t.as_str()
+                        && matches!(
+                            tt,
+                            "object" | "array" | "string" | "number" | "integer" | "boolean"
+                        )
+                    {
+                        ty = Some(tt.to_string());
+                        break;
+                    }
+                }
+            }
+
+            if ty.is_none() {
+                if map.contains_key("properties")
+                    || map.contains_key("required")
+                    || map.contains_key("additionalProperties")
+                {
+                    ty = Some("object".to_string());
+                } else if map.contains_key("items") || map.contains_key("prefixItems") {
+                    ty = Some("array".to_string());
+                } else if map.contains_key("enum")
+                    || map.contains_key("const")
+                    || map.contains_key("format")
+                {
+                    ty = Some("string".to_string());
+                } else if map.contains_key("minimum")
+                    || map.contains_key("maximum")
+                    || map.contains_key("exclusiveMinimum")
+                    || map.contains_key("exclusiveMaximum")
+                    || map.contains_key("multipleOf")
+                {
+                    ty = Some("number".to_string());
+                }
+            }
+
+            let ty = ty.unwrap_or_else(|| "string".to_string());
+            map.insert("type".to_string(), JsonValue::String(ty.clone()));
+
+            if ty == "object" {
+                if !map.contains_key("properties") {
+                    map.insert(
+                        "properties".to_string(),
+                        JsonValue::Object(serde_json::Map::new()),
+                    );
+                }
+                if let Some(ap) = map.get_mut("additionalProperties") {
+                    let is_bool = matches!(ap, JsonValue::Bool(_));
+                    if !is_bool {
+                        sanitize_json_schema(ap);
+                    }
+                }
+            }
+
+            if ty == "array" && !map.contains_key("items") {
+                map.insert("items".to_string(), json!({ "type": "string" }));
+            }
+        }
+        JsonValue::Null | JsonValue::Number(_) | JsonValue::String(_) => {}
+    }
+}