subagents

Co-authored-by: Gabriel Peal <gpeal@users.noreply.github.com>

codex-rs/core/src/codex.rs

@@ -142,6 +142,14 @@ pub struct CodexSpawnOk {
 }
 
 pub(crate) const INITIAL_SUBMIT_ID: &str = "";
+pub(crate) const SUBMISSION_CHANNEL_CAPACITY: usize = 64;
+
+// Model-formatting limits: clients get full streams; oonly content sent to the model is truncated.
+pub(crate) const MODEL_FORMAT_MAX_BYTES: usize = 10 * 1024; // 10 KiB
+pub(crate) const MODEL_FORMAT_MAX_LINES: usize = 256; // lines
+pub(crate) const MODEL_FORMAT_HEAD_LINES: usize = MODEL_FORMAT_MAX_LINES / 2;
+pub(crate) const MODEL_FORMAT_TAIL_LINES: usize = MODEL_FORMAT_MAX_LINES - MODEL_FORMAT_HEAD_LINES; // 128
+pub(crate) const MODEL_FORMAT_HEAD_BYTES: usize = MODEL_FORMAT_MAX_BYTES / 2;
 
 impl Codex {
     /// Spawn a new [`Codex`] and initialize the session.
@@ -150,7 +158,7 @@ impl Codex {
         auth_manager: Arc<AuthManager>,
         initial_history: Option<Vec<ResponseItem>>,
     ) -> CodexResult<CodexSpawnOk> {
-        let (tx_sub, rx_sub) = async_channel::bounded(64);
+        let (tx_sub, rx_sub) = async_channel::bounded(SUBMISSION_CHANNEL_CAPACITY);
         let (tx_event, rx_event) = async_channel::unbounded();
 
         let user_instructions = get_user_instructions(&config).await;
@@ -255,6 +263,15 @@ pub(crate) struct Session {
     /// Manager for external MCP servers/tools.
     mcp_connection_manager: McpConnectionManager,
 
+    /// Loaded subagent definitions from project and user scope.
+    subagents_registry: crate::subagents::registry::SubagentRegistry,
+
+    /// Auth manager used to spawn nested sessions (e.g., subagents).
+    auth_manager: Arc<AuthManager>,
+
+    /// Base configuration used to derive nested session configs.
+    base_config: Arc<Config>,
+
     /// External notifier command (will be passed as args to exec()). When
     /// `None` this feature is disabled.
     notify: Option<Vec<String>>,
@@ -490,6 +507,30 @@ impl Session {
             model_reasoning_summary,
             session_id,
         );
+        // Build subagent registry paths and load once per session
+        let project_agents_dir = {
+            let mut p = cwd.clone();
+            p.push(".codex");
+            p.push("agents");
+            if p.exists() { Some(p) } else { None }
+        };
+        let user_agents_dir = {
+            let mut p = config.codex_home.clone();
+            p.push("agents");
+            if p.exists() { Some(p) } else { None }
+        };
+        let mut subagents_registry =
+            crate::subagents::registry::SubagentRegistry::new(project_agents_dir, user_agents_dir);
+        subagents_registry.load();
+        // Log discovered subagents for visibility in clients (e.g., TUI) after
+        // SessionConfigured so the first event contract remains intact.
+        post_session_configured_error_events.push(Event {
+            id: INITIAL_SUBMIT_ID.to_string(),
+            msg: EventMsg::BackgroundEvent(BackgroundEventEvent {
+                message: format!("subagents discovered: {:?}", subagents_registry.all_names()),
+            }),
+        });
+
         let turn_context = TurnContext {
             client,
             tools_config: ToolsConfig::new(
@@ -498,6 +539,7 @@ impl Session {
                 sandbox_policy.clone(),
                 config.include_plan_tool,
                 config.include_apply_patch_tool,
+                config.include_subagent_tool,
             ),
             user_instructions,
             base_instructions,
@@ -511,6 +553,9 @@ impl Session {
             session_id,
             tx_event: tx_event.clone(),
             mcp_connection_manager,
+            subagents_registry,
+            auth_manager: auth_manager.clone(),
+            base_config: config.clone(),
             notify,
             state: Mutex::new(state),
             rollout: Mutex::new(rollout_recorder),
@@ -570,6 +615,16 @@ impl Session {
         }
     }
 
+    /// Access auth manager for nested sessions.
+    pub(crate) fn auth_manager(&self) -> Arc<AuthManager> {
+        self.auth_manager.clone()
+    }
+
+    /// Access base config for nested sessions.
+    pub(crate) fn base_config(&self) -> Arc<Config> {
+        self.base_config.clone()
+    }
+
     /// Sends the given event to the client and swallows the send event, if
     /// any, logging it as an error.
     pub(crate) async fn send_event(&self, event: Event) {
@@ -722,15 +777,15 @@ impl Session {
         let ExecToolCallOutput {
             stdout,
             stderr,
+            aggregated_output,
             duration,
             exit_code,
         } = output;
-        // Because stdout and stderr could each be up to 100 KiB, we send
-        // truncated versions.
-        const MAX_STREAM_OUTPUT: usize = 5 * 1024; // 5KiB
-        let stdout = stdout.text.chars().take(MAX_STREAM_OUTPUT).collect();
-        let stderr = stderr.text.chars().take(MAX_STREAM_OUTPUT).collect();
+        // Send full stdout/stderr to clients; do not truncate.
+        let stdout = stdout.text.clone();
+        let stderr = stderr.text.clone();
         let formatted_output = format_exec_output_str(output);
+        let aggregated_output: String = aggregated_output.text.clone();
 
         let msg = if is_apply_patch {
             EventMsg::PatchApplyEnd(PatchApplyEndEvent {
@@ -744,9 +799,10 @@ impl Session {
                 call_id: call_id.to_string(),
                 stdout,
                 stderr,
-                formatted_output,
-                duration: *duration,
+                aggregated_output,
                 exit_code: *exit_code,
+                duration: *duration,
+                formatted_output,
             })
         };
 
@@ -804,6 +860,7 @@ impl Session {
                     exit_code: -1,
                     stdout: StreamOutput::new(String::new()),
                     stderr: StreamOutput::new(get_error_message_ui(e)),
+                    aggregated_output: StreamOutput::new(get_error_message_ui(e)),
                     duration: Duration::default(),
                 };
                 &output_stderr
@@ -1080,6 +1137,7 @@ async fn submission_loop(
                     new_sandbox_policy.clone(),
                     config.include_plan_tool,
                     config.include_apply_patch_tool,
+                    config.include_subagent_tool,
                 );
 
                 let new_turn_context = TurnContext {
@@ -1158,6 +1216,7 @@ async fn submission_loop(
                             sandbox_policy.clone(),
                             config.include_plan_tool,
                             config.include_apply_patch_tool,
+                            config.include_subagent_tool,
                         ),
                         user_instructions: turn_context.user_instructions.clone(),
                         base_instructions: turn_context.base_instructions.clone(),
@@ -1544,6 +1603,27 @@ async fn run_turn(
         &turn_context.tools_config,
         Some(sess.mcp_connection_manager.list_all_tools()),
     );
+    tracing::trace!("Tools: {tools:?}");
+
+    // Log tool names for visibility in the TUI/debug logs.
+    #[allow(clippy::match_same_arms)]
+    let tool_names: Vec<String> = tools
+        .iter()
+        .map(|t| match t {
+            crate::openai_tools::OpenAiTool::Function(f) => f.name.clone(),
+            crate::openai_tools::OpenAiTool::LocalShell {} => "local_shell".to_string(),
+            crate::openai_tools::OpenAiTool::Freeform(f) => f.name.clone(),
+        })
+        .collect();
+    let _ = sess
+        .tx_event
+        .send(Event {
+            id: sub_id.clone(),
+            msg: EventMsg::BackgroundEvent(BackgroundEventEvent {
+                message: format!("tools available: {:?}", tool_names),
+            }),
+        })
+        .await;
 
     let prompt = Prompt {
         input,
@@ -2063,6 +2143,84 @@ async fn handle_function_call(
             .await
         }
         "update_plan" => handle_update_plan(sess, arguments, sub_id, call_id).await,
+        "subagent_run" => {
+            #[derive(serde::Deserialize)]
+            struct Args {
+                name: String,
+                input: String,
+                #[serde(default)]
+                context: Option<String>,
+            }
+            let args = match serde_json::from_str::<Args>(&arguments) {
+                Ok(a) => a,
+                Err(e) => {
+                    return ResponseInputItem::FunctionCallOutput {
+                        call_id,
+                        output: FunctionCallOutputPayload {
+                            content: format!("failed to parse function arguments: {e}"),
+                            success: Some(false),
+                        },
+                    };
+                }
+            };
+
+            let result = crate::subagents::runner::run(
+                sess,
+                turn_context,
+                &sess.subagents_registry,
+                crate::subagents::runner::RunSubagentArgs {
+                    name: args.name,
+                    input: args.input,
+                    context: args.context,
+                },
+                &sub_id,
+            )
+            .await;
+
+            match result {
+                Ok(message) => ResponseInputItem::FunctionCallOutput {
+                    call_id,
+                    output: FunctionCallOutputPayload {
+                        content: message,
+                        success: Some(true),
+                    },
+                },
+                Err(e) => ResponseInputItem::FunctionCallOutput {
+                    call_id,
+                    output: FunctionCallOutputPayload {
+                        content: format!("subagent failed: {e}"),
+                        success: Some(false),
+                    },
+                },
+            }
+        }
+        "subagent_list" => {
+            #[derive(serde::Serialize)]
+            struct SubagentBrief<'a> {
+                name: &'a str,
+                description: &'a str,
+            }
+            let mut list = Vec::new();
+            for name in sess.subagents_registry.all_names() {
+                if let Some(def) = sess.subagents_registry.get(&name) {
+                    list.push(SubagentBrief {
+                        name: &def.name,
+                        description: &def.description,
+                    });
+                }
+            }
+            let payload = match serde_json::to_string(&list) {
+                Ok(s) => s,
+                Err(e) => format!("failed to serialize subagent list: {e}"),
+            };
+            ResponseInputItem::FunctionCallOutput {
+                call_id,
+                output: FunctionCallOutputPayload {
+                    content: payload,
+                    success: Some(true),
+                },
+            }
+        }
         _ => {
             match sess.mcp_connection_manager.parse_tool_name(&name) {
                 Some((server, tool_name)) => {
@@ -2173,6 +2331,8 @@ fn parse_container_exec_arguments(
     }
 }
 
+// (helper run_one_turn_collect removed as unused)
+
 pub struct ExecInvokeArgs<'a> {
     pub params: ExecParams,
     pub sandbox_type: SandboxType,
@@ -2550,23 +2710,103 @@ async fn handle_sandbox_error(
 
 fn format_exec_output_str(exec_output: &ExecToolCallOutput) -> String {
     let ExecToolCallOutput {
-        exit_code,
-        stdout,
-        stderr,
-        ..
+        aggregated_output, ..
     } = exec_output;
 
-    let is_success = *exit_code == 0;
-    let output = if is_success { stdout } else { stderr };
+    // Head+tail truncation for the model: show the beginning and end with an elision.
+    // Clients still receive full streams; only this formatted summary is capped.
 
-    let mut formatted_output = output.text.clone();
-    if let Some(truncated_after_lines) = output.truncated_after_lines {
-        formatted_output.push_str(&format!(
-            "\n\n[Output truncated after {truncated_after_lines} lines: too many lines or bytes.]",
-        ));
+    let s = aggregated_output.text.as_str();
+    let total_lines = s.lines().count();
+    if s.len() <= MODEL_FORMAT_MAX_BYTES && total_lines <= MODEL_FORMAT_MAX_LINES {
+        return s.to_string();
     }
 
-    formatted_output
+    let lines: Vec<&str> = s.lines().collect();
+    let head_take = MODEL_FORMAT_HEAD_LINES.min(lines.len());
+    let tail_take = MODEL_FORMAT_TAIL_LINES.min(lines.len().saturating_sub(head_take));
+    let omitted = lines.len().saturating_sub(head_take + tail_take);
+
+    // Join head and tail blocks (lines() strips newlines; reinsert them)
+    let head_block = lines
+        .iter()
+        .take(head_take)
+        .cloned()
+        .collect::<Vec<_>>()
+        .join("\n");
+    let tail_block = if tail_take > 0 {
+        lines[lines.len() - tail_take..].join("\n")
+    } else {
+        String::new()
+    };
+    let marker = format!("\n[... omitted {omitted} of {total_lines} lines ...]\n\n");
+
+    // Byte budgets for head/tail around the marker
+    let mut head_budget = MODEL_FORMAT_HEAD_BYTES.min(MODEL_FORMAT_MAX_BYTES);
+    let tail_budget = MODEL_FORMAT_MAX_BYTES.saturating_sub(head_budget + marker.len());
+    if tail_budget == 0 && marker.len() >= MODEL_FORMAT_MAX_BYTES {
+        // Degenerate case: marker alone exceeds budget; return a clipped marker
+        return take_bytes_at_char_boundary(&marker, MODEL_FORMAT_MAX_BYTES).to_string();
+    }
+    if tail_budget == 0 {
+        // Make room for the marker by shrinking head
+        head_budget = MODEL_FORMAT_MAX_BYTES.saturating_sub(marker.len());
+    }
+
+    // Enforce line-count cap by trimming head/tail lines
+    let head_lines_text = head_block;
+    let tail_lines_text = tail_block;
+    // Build final string respecting byte budgets
+    let head_part = take_bytes_at_char_boundary(&head_lines_text, head_budget);
+    let mut result = String::with_capacity(MODEL_FORMAT_MAX_BYTES.min(s.len()));
+    result.push_str(head_part);
+    result.push_str(&marker);
+
+    let remaining = MODEL_FORMAT_MAX_BYTES.saturating_sub(result.len());
+    let tail_budget_final = remaining;
+    let tail_part = take_last_bytes_at_char_boundary(&tail_lines_text, tail_budget_final);
+    result.push_str(tail_part);
+
+    result
+}
+
+// Truncate a &str to a byte budget at a char boundary (prefix)
+#[inline]
+fn take_bytes_at_char_boundary(s: &str, maxb: usize) -> &str {
+    if s.len() <= maxb {
+        return s;
+    }
+    let mut last_ok = 0;
+    for (i, ch) in s.char_indices() {
+        let nb = i + ch.len_utf8();
+        if nb > maxb {
+            break;
+        }
+        last_ok = nb;
+    }
+    &s[..last_ok]
+}
+
+// Take a suffix of a &str within a byte budget at a char boundary
+#[inline]
+fn take_last_bytes_at_char_boundary(s: &str, maxb: usize) -> &str {
+    if s.len() <= maxb {
+        return s;
+    }
+    let mut start = s.len();
+    let mut used = 0usize;
+    for (i, ch) in s.char_indices().rev() {
+        let nb = ch.len_utf8();
+        if used + nb > maxb {
+            break;
+        }
+        start = i;
+        used += nb;
+        if start == 0 {
+            break;
+        }
+    }
+    &s[start..]
 }
 
 /// Exec output is a pre-serialized JSON payload
@@ -2717,6 +2957,7 @@ mod tests {
     use mcp_types::TextContent;
     use pretty_assertions::assert_eq;
     use serde_json::json;
+    use std::time::Duration as StdDuration;
 
     fn text_block(s: &str) -> ContentBlock {
         ContentBlock::TextContent(TextContent {
@@ -2751,6 +2992,82 @@ mod tests {
         assert_eq!(expected, got);
     }
 
+    #[test]
+    fn model_truncation_head_tail_by_lines() {
+        // Build 400 short lines so line-count limit, not byte budget, triggers truncation
+        let lines: Vec<String> = (1..=400).map(|i| format!("line{i}")).collect();
+        let full = lines.join("\n");
+
+        let exec = ExecToolCallOutput {
+            exit_code: 0,
+            stdout: StreamOutput::new(String::new()),
+            stderr: StreamOutput::new(String::new()),
+            aggregated_output: StreamOutput::new(full.clone()),
+            duration: StdDuration::from_secs(1),
+        };
+
+        let out = format_exec_output_str(&exec);
+
+        // Expect elision marker with correct counts
+        let omitted = 400 - MODEL_FORMAT_MAX_LINES; // 144
+        let marker = format!("\n[... omitted {omitted} of 400 lines ...]\n\n");
+        assert!(out.contains(&marker), "missing marker: {out}");
+
+        // Validate head and tail
+        let parts: Vec<&str> = out.split(&marker).collect();
+        assert_eq!(parts.len(), 2, "expected one marker split");
+        let head = parts[0];
+        let tail = parts[1];
+
+        let expected_head: String = (1..=MODEL_FORMAT_HEAD_LINES)
+            .map(|i| format!("line{i}"))
+            .collect::<Vec<_>>()
+            .join("\n");
+        assert!(head.starts_with(&expected_head), "head mismatch");
+
+        let expected_tail: String = ((400 - MODEL_FORMAT_TAIL_LINES + 1)..=400)
+            .map(|i| format!("line{i}"))
+            .collect::<Vec<_>>()
+            .join("\n");
+        assert!(tail.ends_with(&expected_tail), "tail mismatch");
+    }
+
+    #[test]
+    fn model_truncation_respects_byte_budget() {
+        // Construct a large output (about 100kB) so byte budget dominates
+        let big_line = "x".repeat(100);
+        let full = std::iter::repeat_n(big_line.clone(), 1000)
+            .collect::<Vec<_>>()
+            .join("\n");
+
+        let exec = ExecToolCallOutput {
+            exit_code: 0,
+            stdout: StreamOutput::new(String::new()),
+            stderr: StreamOutput::new(String::new()),
+            aggregated_output: StreamOutput::new(full.clone()),
+            duration: StdDuration::from_secs(1),
+        };
+
+        let out = format_exec_output_str(&exec);
+        assert!(out.len() <= MODEL_FORMAT_MAX_BYTES, "exceeds byte budget");
+        assert!(out.contains("omitted"), "should contain elision marker");
+
+        // Ensure head and tail are drawn from the original
+        assert!(full.starts_with(out.chars().take(8).collect::<String>().as_str()));
+        assert!(
+            full.ends_with(
+                out.chars()
+                    .rev()
+                    .take(8)
+                    .collect::<String>()
+                    .chars()
+                    .rev()
+                    .collect::<String>()
+                    .as_str()
+            )
+        );
+    }
+
     #[test]
     fn falls_back_to_content_when_structured_is_null() {
         let ctr = CallToolResult {

codex-rs/core/src/config.rs

@@ -169,6 +169,9 @@ pub struct Config {
     /// model family's default preference.
     pub include_apply_patch_tool: bool,
 
+    /// Include the `subagent.run` tool allowing the model to invoke configured subagents.
+    pub include_subagent_tool: bool,
+
     /// The value for the `originator` header included with Responses API requests.
     pub responses_originator_header: String,
 
@@ -476,6 +479,9 @@ pub struct ConfigToml {
 
     /// If set to `true`, the API key will be signed with the `originator` header.
     pub preferred_auth_method: Option<AuthMode>,
+
+    /// Include the `subagent.run` tool allowing the model to invoke configured subagents.
+    pub include_subagent_tool: Option<bool>,
 }
 
 #[derive(Deserialize, Debug, Clone, PartialEq, Eq)]
@@ -570,6 +576,7 @@ pub struct ConfigOverrides {
     pub base_instructions: Option<String>,
     pub include_plan_tool: Option<bool>,
     pub include_apply_patch_tool: Option<bool>,
+    pub include_subagent_tool: Option<bool>,
     pub disable_response_storage: Option<bool>,
     pub show_raw_agent_reasoning: Option<bool>,
 }
@@ -596,6 +603,7 @@ impl Config {
             base_instructions,
             include_plan_tool,
             include_apply_patch_tool,
+            include_subagent_tool,
             disable_response_storage,
             show_raw_agent_reasoning,
         } = overrides;
@@ -756,6 +764,11 @@ impl Config {
             experimental_resume,
             include_plan_tool: include_plan_tool.unwrap_or(false),
             include_apply_patch_tool: include_apply_patch_tool.unwrap_or(false),
+            include_subagent_tool: config_profile
+                .include_subagent_tool
+                .or(cfg.include_subagent_tool)
+                .or(include_subagent_tool)
+                .unwrap_or(false),
             responses_originator_header,
             preferred_auth_method: cfg.preferred_auth_method.unwrap_or(AuthMode::ChatGPT),
         };
@@ -1122,6 +1135,7 @@ disable_response_storage = true
                 base_instructions: None,
                 include_plan_tool: false,
                 include_apply_patch_tool: false,
+                include_subagent_tool: false,
                 responses_originator_header: "codex_cli_rs".to_string(),
                 preferred_auth_method: AuthMode::ChatGPT,
             },
@@ -1176,6 +1190,7 @@ disable_response_storage = true
             base_instructions: None,
             include_plan_tool: false,
             include_apply_patch_tool: false,
+            include_subagent_tool: false,
             responses_originator_header: "codex_cli_rs".to_string(),
             preferred_auth_method: AuthMode::ChatGPT,
         };
@@ -1245,6 +1260,7 @@ disable_response_storage = true
             base_instructions: None,
             include_plan_tool: false,
             include_apply_patch_tool: false,
+            include_subagent_tool: false,
             responses_originator_header: "codex_cli_rs".to_string(),
             preferred_auth_method: AuthMode::ChatGPT,
         };

codex-rs/core/src/config_profile.rs

@@ -21,4 +21,6 @@ pub struct ConfigProfile {
     pub model_verbosity: Option<Verbosity>,
     pub chatgpt_base_url: Option<String>,
     pub experimental_instructions_file: Option<PathBuf>,
+    /// Include the `subagent.run` tool allowing the model to invoke configured subagents.
+    pub include_subagent_tool: Option<bool>,
 }

codex-rs/core/src/exec.rs

@@ -28,18 +28,17 @@ use crate::spawn::StdioPolicy;
 use crate::spawn::spawn_child_async;
 use serde_bytes::ByteBuf;
 
-// Maximum we send for each stream, which is either:
-// - 10KiB OR
-// - 256 lines
-const MAX_STREAM_OUTPUT: usize = 10 * 1024;
-const MAX_STREAM_OUTPUT_LINES: usize = 256;
-
 const DEFAULT_TIMEOUT_MS: u64 = 10_000;
 
 // Hardcode these since it does not seem worth including the libc crate just
 // for these.
 const SIGKILL_CODE: i32 = 9;
 const TIMEOUT_CODE: i32 = 64;
+const EXIT_CODE_SIGNAL_BASE: i32 = 128; // conventional shell: 128 + signal
+
+// I/O buffer sizing
+const READ_CHUNK_SIZE: usize = 8192; // bytes per read
+const AGGREGATE_BUFFER_INITIAL_CAPACITY: usize = 8 * 1024; // 8 KiB
 
 #[derive(Debug, Clone)]
 pub struct ExecParams {
@@ -153,6 +152,7 @@ pub async fn process_exec_tool_call(
                 exit_code,
                 stdout,
                 stderr,
+                aggregated_output: raw_output.aggregated_output.from_utf8_lossy(),
                 duration,
             })
         }
@@ -189,10 +189,11 @@ pub struct StreamOutput<T> {
     pub truncated_after_lines: Option<u32>,
 }
 #[derive(Debug)]
-pub struct RawExecToolCallOutput {
+struct RawExecToolCallOutput {
     pub exit_status: ExitStatus,
     pub stdout: StreamOutput<Vec<u8>>,
     pub stderr: StreamOutput<Vec<u8>>,
+    pub aggregated_output: StreamOutput<Vec<u8>>,
 }
 
 impl StreamOutput<String> {
@@ -213,11 +214,17 @@ impl StreamOutput<Vec<u8>> {
     }
 }
 
+#[inline]
+fn append_all(dst: &mut Vec<u8>, src: &[u8]) {
+    dst.extend_from_slice(src);
+}
+
 #[derive(Debug)]
 pub struct ExecToolCallOutput {
     pub exit_code: i32,
     pub stdout: StreamOutput<String>,
     pub stderr: StreamOutput<String>,
+    pub aggregated_output: StreamOutput<String>,
     pub duration: Duration,
 }
 
@@ -253,7 +260,7 @@ async fn exec(
 
 /// Consumes the output of a child process, truncating it so it is suitable for
 /// use as the output of a `shell` tool call. Also enforces specified timeout.
-pub(crate) async fn consume_truncated_output(
+async fn consume_truncated_output(
     mut child: Child,
     timeout: Duration,
     stdout_stream: Option<StdoutStream>,
@@ -273,19 +280,19 @@ pub(crate) async fn consume_truncated_output(
         ))
     })?;
 
+    let (agg_tx, agg_rx) = async_channel::unbounded::<Vec<u8>>();
+
     let stdout_handle = tokio::spawn(read_capped(
         BufReader::new(stdout_reader),
-        MAX_STREAM_OUTPUT,
-        MAX_STREAM_OUTPUT_LINES,
         stdout_stream.clone(),
         false,
+        Some(agg_tx.clone()),
     ));
     let stderr_handle = tokio::spawn(read_capped(
         BufReader::new(stderr_reader),
-        MAX_STREAM_OUTPUT,
-        MAX_STREAM_OUTPUT_LINES,
         stdout_stream.clone(),
         true,
+        Some(agg_tx.clone()),
     ));
 
     let exit_status = tokio::select! {
@@ -297,38 +304,48 @@ pub(crate) async fn consume_truncated_output(
                     // timeout
                     child.start_kill()?;
                     // Debatable whether `child.wait().await` should be called here.
-                    synthetic_exit_status(128 + TIMEOUT_CODE)
+                    synthetic_exit_status(EXIT_CODE_SIGNAL_BASE + TIMEOUT_CODE)
                 }
             }
         }
         _ = tokio::signal::ctrl_c() => {
             child.start_kill()?;
-            synthetic_exit_status(128 + SIGKILL_CODE)
+            synthetic_exit_status(EXIT_CODE_SIGNAL_BASE + SIGKILL_CODE)
         }
     };
 
     let stdout = stdout_handle.await??;
     let stderr = stderr_handle.await??;
 
+    drop(agg_tx);
+
+    let mut combined_buf = Vec::with_capacity(AGGREGATE_BUFFER_INITIAL_CAPACITY);
+    while let Ok(chunk) = agg_rx.recv().await {
+        append_all(&mut combined_buf, &chunk);
+    }
+    let aggregated_output = StreamOutput {
+        text: combined_buf,
+        truncated_after_lines: None,
+    };
+
     Ok(RawExecToolCallOutput {
         exit_status,
         stdout,
         stderr,
+        aggregated_output,
     })
 }
 
 async fn read_capped<R: AsyncRead + Unpin + Send + 'static>(
     mut reader: R,
-    max_output: usize,
-    max_lines: usize,
     stream: Option<StdoutStream>,
     is_stderr: bool,
+    aggregate_tx: Option<Sender<Vec<u8>>>,
 ) -> io::Result<StreamOutput<Vec<u8>>> {
-    let mut buf = Vec::with_capacity(max_output.min(8 * 1024));
-    let mut tmp = [0u8; 8192];
+    let mut buf = Vec::with_capacity(AGGREGATE_BUFFER_INITIAL_CAPACITY);
+    let mut tmp = [0u8; READ_CHUNK_SIZE];
 
-    let mut remaining_bytes = max_output;
-    let mut remaining_lines = max_lines;
+    // No caps: append all bytes
 
     loop {
         let n = reader.read(&mut tmp).await?;
@@ -355,33 +372,17 @@ async fn read_capped<R: AsyncRead + Unpin + Send + 'static>(
             let _ = stream.tx_event.send(event).await;
         }
 
-        // Copy into the buffer only while we still have byte and line budget.
-        if remaining_bytes > 0 && remaining_lines > 0 {
-            let mut copy_len = 0;
-            for &b in &tmp[..n] {
-                if remaining_bytes == 0 || remaining_lines == 0 {
-                    break;
-                }
-                copy_len += 1;
-                remaining_bytes -= 1;
-                if b == b'\n' {
-                    remaining_lines -= 1;
-                }
-            }
-            buf.extend_from_slice(&tmp[..copy_len]);
+        if let Some(tx) = &aggregate_tx {
+            let _ = tx.send(tmp[..n].to_vec()).await;
         }
-        // Continue reading to EOF to avoid back-pressure, but discard once caps are hit.
-    }
 
-    let truncated = remaining_lines == 0 || remaining_bytes == 0;
+        append_all(&mut buf, &tmp[..n]);
+        // Continue reading to EOF to avoid back-pressure
+    }
 
     Ok(StreamOutput {
         text: buf,
-        truncated_after_lines: if truncated {
-            Some((max_lines - remaining_lines) as u32)
-        } else {
-            None
-        },
+        truncated_after_lines: None,
     })
 }
 

codex-rs/core/src/lib.rs

@@ -62,3 +62,4 @@ pub use codex_protocol::protocol;
 // Re-export protocol config enums to ensure call sites can use the same types
 // as those in the protocol crate when constructing protocol messages.
 pub use codex_protocol::config_types as protocol_config_types;
+pub mod subagents;

codex-rs/core/src/openai_tools.rs

@@ -63,6 +63,7 @@ pub struct ToolsConfig {
     pub shell_type: ConfigShellToolType,
     pub plan_tool: bool,
     pub apply_patch_tool_type: Option<ApplyPatchToolType>,
+    pub subagent_tool: bool,
 }
 
 impl ToolsConfig {
@@ -72,6 +73,7 @@ impl ToolsConfig {
         sandbox_policy: SandboxPolicy,
         include_plan_tool: bool,
         include_apply_patch_tool: bool,
+        include_subagent_tool: bool,
     ) -> Self {
         let mut shell_type = if model_family.uses_local_shell_tool {
             ConfigShellToolType::LocalShell
@@ -100,6 +102,7 @@ impl ToolsConfig {
             shell_type,
             plan_tool: include_plan_tool,
             apply_patch_tool_type,
+            subagent_tool: include_subagent_tool,
         }
     }
 }
@@ -509,6 +512,12 @@ pub(crate) fn get_openai_tools(
         }
     }
 
+    if config.subagent_tool {
+        tracing::trace!("Adding subagent tool");
+        tools.push(crate::subagents::SUBAGENT_TOOL.clone());
+        tools.push(crate::subagents::SUBAGENT_LIST_TOOL.clone());
+    }
+
     if let Some(mcp_tools) = mcp_tools {
         for (name, tool) in mcp_tools {
             match mcp_tool_to_openai_tool(name.clone(), tool.clone()) {
@@ -520,6 +529,7 @@ pub(crate) fn get_openai_tools(
         }
     }
 
+    tracing::trace!("Tools: {tools:?}");
     tools
 }
 
@@ -564,6 +574,7 @@ mod tests {
             SandboxPolicy::ReadOnly,
             true,
             false,
+            false,
         );
         let tools = get_openai_tools(&config, Some(HashMap::new()));
 
@@ -579,6 +590,7 @@ mod tests {
             SandboxPolicy::ReadOnly,
             true,
             false,
+            false,
         );
         let tools = get_openai_tools(&config, Some(HashMap::new()));
 
@@ -594,6 +606,7 @@ mod tests {
             SandboxPolicy::ReadOnly,
             false,
             false,
+            false,
         );
         let tools = get_openai_tools(
             &config,
@@ -688,6 +701,7 @@ mod tests {
             SandboxPolicy::ReadOnly,
             false,
             false,
+            false,
         );
 
         let tools = get_openai_tools(
@@ -744,6 +758,7 @@ mod tests {
             SandboxPolicy::ReadOnly,
             false,
             false,
+            false,
         );
 
         let tools = get_openai_tools(
@@ -795,6 +810,7 @@ mod tests {
             SandboxPolicy::ReadOnly,
             false,
             false,
+            false,
         );
 
         let tools = get_openai_tools(
@@ -849,6 +865,7 @@ mod tests {
             SandboxPolicy::ReadOnly,
             false,
             false,
+            false,
         );
 
         let tools = get_openai_tools(

codex-rs/core/src/subagents/definition.rs

@@ -0,0 +1,32 @@
+use serde::Deserialize;
+use std::fs;
+use std::path::Path;
+
+#[derive(Debug, Clone, Deserialize)]
+pub struct SubagentDefinition {
+    pub name: String,
+    pub description: String,
+    /// Base instructions for this subagent.
+    pub instructions: String,
+    /// When not set, inherits the parent agent's tool set. When set to an
+    /// empty list, no tools are available to the subagent.
+    #[serde(default)]
+    pub tools: Option<Vec<String>>, // None => inherit; Some(vec) => allow-list
+}
+
+impl SubagentDefinition {
+    pub fn from_json_str(s: &str) -> Result<Self, serde_json::Error> {
+        serde_json::from_str::<Self>(s)
+    }
+
+    pub fn from_file(path: &Path) -> std::io::Result<Self> {
+        let contents = fs::read_to_string(path)?;
+        // Surface JSON parsing error with file context
+        serde_json::from_str::<Self>(&contents).map_err(|e| {
+            std::io::Error::new(
+                std::io::ErrorKind::InvalidData,
+                format!("invalid subagent JSON at {}: {e}", path.display()),
+            )
+        })
+    }
+}

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

@@ -0,0 +1,6 @@
+pub mod definition;
+pub mod registry;
+pub mod runner;
+pub mod tool;
+
+pub(crate) use tool::{SUBAGENT_LIST_TOOL, SUBAGENT_TOOL};

codex-rs/core/src/subagents/registry.rs

@@ -0,0 +1,92 @@
+use super::definition::SubagentDefinition;
+use std::collections::HashMap;
+use std::fs;
+use std::path::Path;
+use std::path::PathBuf;
+
+#[derive(Debug, Default, Clone)]
+pub struct SubagentRegistry {
+    /// Directory under the project (cwd/.codex/agents).
+    project_dir: Option<PathBuf>,
+    /// Directory under CODEX_HOME (~/.codex/agents).
+    user_dir: Option<PathBuf>,
+    /// Merged map: project definitions override user ones.
+    map: HashMap<String, SubagentDefinition>,
+}
+
+impl SubagentRegistry {
+    pub fn new(project_dir: Option<PathBuf>, user_dir: Option<PathBuf>) -> Self {
+        Self {
+            project_dir,
+            user_dir,
+            map: HashMap::new(),
+        }
+    }
+
+    /// Loads JSON files from user_dir then project_dir (project wins on conflict).
+    pub fn load(&mut self) {
+        let mut map: HashMap<String, SubagentDefinition> = HashMap::new();
+
+        // Load user definitions first
+        if let Some(dir) = &self.user_dir {
+            Self::load_from_dir_into(dir, &mut map);
+        }
+        // Then load project definitions which override on conflicts
+        if let Some(dir) = &self.project_dir {
+            Self::load_from_dir_into(dir, &mut map);
+        }
+
+        // Ensure a simple built‑in test subagent exists to validate wiring end‑to‑end.
+        // Users can override this by providing their own definition named "hello".
+        if !map.contains_key("hello") {
+            map.insert(
+                "hello".to_string(),
+                SubagentDefinition {
+                    name: "hello".to_string(),
+                    description: "Built‑in test subagent that replies with a greeting".to_string(),
+                    // Keep instructions narrow so models reliably output the intended text.
+                    instructions:
+                        "Reply with exactly this text and nothing else: Hello from subagent"
+                            .to_string(),
+                    // Disallow tool usage for the hello subagent.
+                    tools: Some(Vec::new()),
+                },
+            );
+        }
+
+        self.map = map;
+    }
+
+    pub fn get(&self, name: &str) -> Option<&SubagentDefinition> {
+        self.map.get(name)
+    }
+
+    pub fn all_names(&self) -> Vec<String> {
+        self.map.keys().cloned().collect()
+    }
+
+    fn load_from_dir_into(dir: &Path, out: &mut HashMap<String, SubagentDefinition>) {
+        let Ok(iter) = fs::read_dir(dir) else {
+            return;
+        };
+        for entry in iter.flatten() {
+            let path = entry.path();
+            if path.is_file()
+                && path
+                    .extension()
+                    .and_then(|e| e.to_str())
+                    .map(|e| e.eq_ignore_ascii_case("json"))
+                    .unwrap_or(false)
+            {
+                match SubagentDefinition::from_file(&path) {
+                    Ok(def) => {
+                        out.insert(def.name.clone(), def);
+                    }
+                    Err(e) => {
+                        tracing::warn!("Failed to load subagent from {}: {}", path.display(), e);
+                    }
+                }
+            }
+        }
+    }
+}

codex-rs/core/src/subagents/runner.rs

@@ -0,0 +1,142 @@
+use crate::codex::Codex;
+use crate::error::Result as CodexResult;
+
+use super::definition::SubagentDefinition;
+use super::registry::SubagentRegistry;
+
+/// Arguments expected for the `subagent.run` tool.
+#[derive(serde::Deserialize)]
+pub struct RunSubagentArgs {
+    pub name: String,
+    pub input: String,
+    #[serde(default)]
+    pub context: Option<String>,
+}
+
+/// Run a subagent in a nested Codex session and return the final message.
+pub(crate) async fn run(
+    sess: &crate::codex::Session,
+    turn_context: &crate::codex::TurnContext,
+    registry: &SubagentRegistry,
+    args: RunSubagentArgs,
+    _parent_sub_id: &str,
+) -> CodexResult<String> {
+    let def: &SubagentDefinition = registry.get(&args.name).ok_or_else(|| {
+        crate::error::CodexErr::Stream(format!("unknown subagent: {}", args.name), None)
+    })?;
+
+    let mut nested_cfg = (*sess.base_config()).clone();
+    nested_cfg.base_instructions = Some(def.instructions.clone());
+    nested_cfg.user_instructions = None;
+    nested_cfg.approval_policy = turn_context.approval_policy;
+    nested_cfg.sandbox_policy = turn_context.sandbox_policy.clone();
+    nested_cfg.cwd = turn_context.cwd.clone();
+    nested_cfg.include_subagent_tool = false;
+
+    let nested = Codex::spawn(nested_cfg, sess.auth_manager(), None).await?;
+    let nested_codex = nested.codex;
+
+    let subagent_id = uuid::Uuid::new_v4().to_string();
+    forward_begin(sess, _parent_sub_id, &subagent_id, &def.name).await;
+
+    let text = match args.context {
+        Some(ctx) if !ctx.trim().is_empty() => format!("{ctx}\n\n{input}", input = args.input),
+        _ => args.input,
+    };
+
+    nested_codex
+        .submit(crate::protocol::Op::UserInput {
+            items: vec![crate::protocol::InputItem::Text { text }],
+        })
+        .await
+        .map_err(|e| {
+            crate::error::CodexErr::Stream(format!("failed to submit to subagent: {e}"), None)
+        })?;
+
+    let mut last_message: Option<String> = None;
+    loop {
+        let ev = nested_codex.next_event().await?;
+        match ev.msg.clone() {
+            crate::protocol::EventMsg::AgentMessage(m) => {
+                last_message = Some(m.message);
+            }
+            crate::protocol::EventMsg::TaskComplete(t) => {
+                let _ = nested_codex.submit(crate::protocol::Op::Shutdown).await;
+                forward_forwarded(sess, _parent_sub_id, &subagent_id, &def.name, ev.msg).await;
+                forward_end(
+                    sess,
+                    _parent_sub_id,
+                    &subagent_id,
+                    &def.name,
+                    true,
+                    t.last_agent_message.clone(),
+                )
+                .await;
+                return Ok(t
+                    .last_agent_message
+                    .unwrap_or_else(|| last_message.unwrap_or_default()));
+            }
+            _ => {}
+        }
+        forward_forwarded(sess, _parent_sub_id, &subagent_id, &def.name, ev.msg).await;
+    }
+}
+
+async fn forward_begin(
+    sess: &crate::codex::Session,
+    parent_sub_id: &str,
+    subagent_id: &str,
+    name: &str,
+) {
+    sess
+        .send_event(crate::protocol::Event {
+            id: parent_sub_id.to_string(),
+            msg: crate::protocol::EventMsg::SubagentBegin(crate::protocol::SubagentBeginEvent {
+                subagent_id: subagent_id.to_string(),
+                name: name.to_string(),
+            }),
+        })
+        .await;
+}
+
+async fn forward_forwarded(
+    sess: &crate::codex::Session,
+    parent_sub_id: &str,
+    subagent_id: &str,
+    name: &str,
+    msg: crate::protocol::EventMsg,
+) {
+    sess
+        .send_event(crate::protocol::Event {
+            id: parent_sub_id.to_string(),
+            msg: crate::protocol::EventMsg::SubagentForwarded(
+                crate::protocol::SubagentForwardedEvent {
+                    subagent_id: subagent_id.to_string(),
+                    name: name.to_string(),
+                    event: Box::new(msg),
+                },
+            ),
+        })
+        .await;
+}
+
+async fn forward_end(
+    sess: &crate::codex::Session,
+    parent_sub_id: &str,
+    subagent_id: &str,
+    name: &str,
+    success: bool,
+    last_agent_message: Option<String>,
+) {
+    sess
+        .send_event(crate::protocol::Event {
+            id: parent_sub_id.to_string(),
+            msg: crate::protocol::EventMsg::SubagentEnd(crate::protocol::SubagentEndEvent {
+                subagent_id: subagent_id.to_string(),
+                name: name.to_string(),
+                success,
+                last_agent_message,
+            }),
+        })
+        .await;
+}

codex-rs/core/src/subagents/tool.rs

@@ -0,0 +1,54 @@
+use std::collections::BTreeMap;
+use std::sync::LazyLock;
+
+use crate::openai_tools::JsonSchema;
+use crate::openai_tools::OpenAiTool;
+use crate::openai_tools::ResponsesApiTool;
+
+pub(crate) static SUBAGENT_TOOL: LazyLock<OpenAiTool> = LazyLock::new(|| {
+    let mut properties = BTreeMap::new();
+    properties.insert(
+        "name".to_string(),
+        JsonSchema::String {
+            description: Some("Registered subagent name".to_string()),
+        },
+    );
+    properties.insert(
+        "input".to_string(),
+        JsonSchema::String {
+            description: Some("Task or instruction for the subagent".to_string()),
+        },
+    );
+    properties.insert(
+        "context".to_string(),
+        JsonSchema::String {
+            description: Some("Optional extra context to aid the task".to_string()),
+        },
+    );
+
+    OpenAiTool::Function(ResponsesApiTool {
+        name: "subagent_run".to_string(),
+        description: "Invoke a named subagent with isolated context and return its result"
+            .to_string(),
+        strict: false,
+        parameters: JsonSchema::Object {
+            properties,
+            required: Some(vec!["name".to_string(), "input".to_string()]),
+            additional_properties: Some(false),
+        },
+    })
+});
+
+pub(crate) static SUBAGENT_LIST_TOOL: LazyLock<OpenAiTool> = LazyLock::new(|| {
+    let properties = BTreeMap::new();
+    OpenAiTool::Function(ResponsesApiTool {
+        name: "subagent_list".to_string(),
+        description: "List available subagents (name and description). Call before subagent_run if unsure.".to_string(),
+        strict: false,
+        parameters: JsonSchema::Object {
+            properties,
+            required: None,
+            additional_properties: Some(false),
+        },
+    })
+});

codex-rs/core/tests/exec.rs

@@ -70,12 +70,12 @@ async fn truncates_output_lines() {
 
     let output = run_test_cmd(tmp, cmd).await.unwrap();
 
-    let expected_output = (1..=256)
+    let expected_output = (1..=300)
         .map(|i| format!("{i}\n"))
         .collect::<Vec<_>>()
         .join("");
     assert_eq!(output.stdout.text, expected_output);
-    assert_eq!(output.stdout.truncated_after_lines, Some(256));
+    assert_eq!(output.stdout.truncated_after_lines, None);
 }
 
 /// Command succeeds with exit code 0 normally
@@ -91,8 +91,8 @@ async fn truncates_output_bytes() {
 
     let output = run_test_cmd(tmp, cmd).await.unwrap();
 
-    assert_eq!(output.stdout.text.len(), 10240);
-    assert_eq!(output.stdout.truncated_after_lines, Some(10));
+    assert!(output.stdout.text.len() >= 15000);
+    assert_eq!(output.stdout.truncated_after_lines, None);
 }
 
 /// Command not found returns exit code 127, this is not considered a sandbox error

codex-rs/core/tests/exec_stream_events.rs

@@ -139,3 +139,34 @@ async fn test_exec_stderr_stream_events_echo() {
     }
     assert_eq!(String::from_utf8_lossy(&err), "oops\n");
 }
+
+#[tokio::test]
+async fn test_aggregated_output_interleaves_in_order() {
+    // Spawn a shell that alternates stdout and stderr with sleeps to enforce order.
+    let cmd = vec![
+        "/bin/sh".to_string(),
+        "-c".to_string(),
+        "printf 'O1\\n'; sleep 0.01; printf 'E1\\n' 1>&2; sleep 0.01; printf 'O2\\n'; sleep 0.01; printf 'E2\\n' 1>&2".to_string(),
+    ];
+
+    let params = ExecParams {
+        command: cmd,
+        cwd: std::env::current_dir().unwrap_or_else(|_| PathBuf::from(".")),
+        timeout_ms: Some(5_000),
+        env: HashMap::new(),
+        with_escalated_permissions: None,
+        justification: None,
+    };
+
+    let policy = SandboxPolicy::new_read_only_policy();
+
+    let result = process_exec_tool_call(params, SandboxType::None, &policy, &None, None)
+        .await
+        .expect("process_exec_tool_call");
+
+    assert_eq!(result.exit_code, 0);
+    assert_eq!(result.stdout.text, "O1\nO2\n");
+    assert_eq!(result.stderr.text, "E1\nE2\n");
+    assert_eq!(result.aggregated_output.text, "O1\nE1\nO2\nE2\n");
+    assert_eq!(result.aggregated_output.truncated_after_lines, None);
+}

codex-rs/exec/src/event_processor_with_human_output.rs

@@ -168,6 +168,15 @@ impl EventProcessor for EventProcessorWithHumanOutput {
     fn process_event(&mut self, event: Event) -> CodexStatus {
         let Event { id: _, msg } = event;
         match msg {
+            EventMsg::SubagentBegin(_) => {
+                // Ignore in human output for now.
+            }
+            EventMsg::SubagentForwarded(_) => {
+                // Ignore; TUI will render forwarded events.
+            }
+            EventMsg::SubagentEnd(_) => {
+                // Ignore in human output for now.
+            }
             EventMsg::Error(ErrorEvent { message }) => {
                 let prefix = "ERROR:".style(self.red);
                 ts_println!(self, "{prefix} {message}");
@@ -287,8 +296,7 @@ impl EventProcessor for EventProcessorWithHumanOutput {
             EventMsg::ExecCommandOutputDelta(_) => {}
             EventMsg::ExecCommandEnd(ExecCommandEndEvent {
                 call_id,
-                stdout,
-                stderr,
+                aggregated_output,
                 duration,
                 exit_code,
                 ..
@@ -304,8 +312,7 @@ impl EventProcessor for EventProcessorWithHumanOutput {
                     ("".to_string(), format!("exec('{call_id}')"))
                 };
 
-                let output = if exit_code == 0 { stdout } else { stderr };
-                let truncated_output = output
+                let truncated_output = aggregated_output
                     .lines()
                     .take(MAX_OUTPUT_LINES_FOR_EXEC_TOOL_CALL)
                     .collect::<Vec<_>>()

codex-rs/exec/src/event_processor_with_json_output.rs

@@ -41,6 +41,12 @@ impl EventProcessor for EventProcessorWithJsonOutput {
 
     fn process_event(&mut self, event: Event) -> CodexStatus {
         match event.msg {
+            EventMsg::SubagentBegin(_)
+            | EventMsg::SubagentForwarded(_)
+            | EventMsg::SubagentEnd(_) => {
+                // Ignored for JSON output in exec for now.
+                CodexStatus::Running
+            }
             EventMsg::AgentMessageDelta(_) | EventMsg::AgentReasoningDelta(_) => {
                 // Suppress streaming events in JSON mode.
                 CodexStatus::Running

codex-rs/exec/src/lib.rs

@@ -146,6 +146,7 @@ pub async fn run_main(cli: Cli, codex_linux_sandbox_exe: Option<PathBuf>) -> any
         model_provider,
         codex_linux_sandbox_exe,
         base_instructions: None,
+        include_subagent_tool: None,
         include_plan_tool: None,
         include_apply_patch_tool: None,
         disable_response_storage: oss.then_some(true),

codex-rs/mcp-server/src/codex_message_processor.rs

@@ -736,6 +736,7 @@ fn derive_config_from_params(
         base_instructions,
         include_plan_tool,
         include_apply_patch_tool,
+        include_subagent_tool: None,
         disable_response_storage: None,
         show_raw_agent_reasoning: None,
     };

codex-rs/mcp-server/src/codex_tool_config.rs

@@ -161,6 +161,7 @@ impl CodexToolCallParam {
             base_instructions,
             include_plan_tool,
             include_apply_patch_tool: None,
+            include_subagent_tool: None,
             disable_response_storage: None,
             show_raw_agent_reasoning: None,
         };

codex-rs/mcp-server/src/codex_tool_runner.rs

@@ -174,6 +174,11 @@ async fn run_codex_tool_session_inner(
                     .await;
 
                 match event.msg {
+                    EventMsg::SubagentBegin(_)
+                    | EventMsg::SubagentForwarded(_)
+                    | EventMsg::SubagentEnd(_) => {
+                        // Ignore subagent orchestration for MCP echoing.
+                    }
                     EventMsg::ExecApprovalRequest(ExecApprovalRequestEvent {
                         command,
                         cwd,

codex-rs/protocol/src/protocol.rs

@@ -478,6 +478,14 @@ pub enum EventMsg {
     ShutdownComplete,
 
     ConversationHistory(ConversationHistoryResponseEvent),
+
+    // --- Subagent orchestration events ---
+    /// Emitted when a subagent starts.
+    SubagentBegin(SubagentBeginEvent),
+    /// Forwards a nested event produced by a running subagent.
+    SubagentForwarded(SubagentForwardedEvent),
+    /// Emitted when a subagent finishes.
+    SubagentEnd(SubagentEndEvent),
 }
 
 // Individual event payload types matching each `EventMsg` variant.
@@ -501,6 +509,28 @@ pub struct TokenUsage {
     pub total_tokens: u64,
 }
 
+#[derive(Debug, Clone, Deserialize, Serialize)]
+pub struct SubagentBeginEvent {
+    pub subagent_id: String,
+    pub name: String,
+}
+
+#[derive(Debug, Clone, Deserialize, Serialize)]
+pub struct SubagentEndEvent {
+    pub subagent_id: String,
+    pub name: String,
+    pub success: bool,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub last_agent_message: Option<String>,
+}
+
+#[derive(Debug, Clone, Deserialize, Serialize)]
+pub struct SubagentForwardedEvent {
+    pub subagent_id: String,
+    pub name: String,
+    pub event: Box<EventMsg>,
+}
+
 impl TokenUsage {
     pub fn is_zero(&self) -> bool {
         self.total_tokens == 0
@@ -685,6 +715,9 @@ pub struct ExecCommandEndEvent {
     pub stdout: String,
     /// Captured stderr
     pub stderr: String,
+    /// Captured aggregated output
+    #[serde(default)]
+    pub aggregated_output: String,
     /// The command's exit code.
     pub exit_code: i32,
     /// The duration of the command execution.

codex-rs/tui/src/chatwidget.rs

@@ -836,8 +836,39 @@ impl ChatWidget {
             EventMsg::ShutdownComplete => self.on_shutdown_complete(),
             EventMsg::TurnDiff(TurnDiffEvent { unified_diff }) => self.on_turn_diff(unified_diff),
             EventMsg::BackgroundEvent(BackgroundEventEvent { message }) => {
+                // Also show background logs in the transcript for visibility.
+                self.add_to_history(history_cell::new_log_line(message.clone()));
                 self.on_background_event(message)
             }
+            EventMsg::SubagentBegin(ev) => {
+                let msg = format!("subagent begin: {} ({})", ev.name, ev.subagent_id);
+                self.add_to_history(history_cell::new_log_line(msg));
+            }
+            EventMsg::SubagentForwarded(ev) => {
+                // Summarize forwarded event type; include message text when it is AgentMessage.
+                match *ev.event {
+                    EventMsg::AgentMessage(AgentMessageEvent { message }) => {
+                        let msg = format!("subagent {}: {}", ev.name, message);
+                        self.add_to_history(history_cell::new_log_line(msg));
+                    }
+                    EventMsg::AgentMessageDelta(AgentMessageDeltaEvent { ref delta }) => {
+                        let msg = format!("subagent {}: {}", ev.name, delta);
+                        self.add_to_history(history_cell::new_log_line(msg));
+                    }
+                    ref other => {
+                        let msg = format!("subagent {} forwarded: {:?}", ev.name, other);
+                        self.add_to_history(history_cell::new_log_line(msg));
+                    }
+                }
+            }
+            EventMsg::SubagentEnd(ev) => {
+                let summary = ev.last_agent_message.as_deref().unwrap_or("");
+                let msg = format!(
+                    "subagent end: {} ({}) success={} {}",
+                    ev.name, ev.subagent_id, ev.success, summary
+                );
+                self.add_to_history(history_cell::new_log_line(msg));
+            }
             EventMsg::StreamError(StreamErrorEvent { message }) => self.on_stream_error(message),
             EventMsg::ConversationHistory(_) => {}
         }

codex-rs/tui/src/chatwidget/tests.rs

@@ -263,6 +263,7 @@ fn exec_history_cell_shows_working_then_completed() {
             call_id: "call-1".into(),
             stdout: "done".into(),
             stderr: String::new(),
+            aggregated_output: "done".into(),
             exit_code: 0,
             duration: std::time::Duration::from_millis(5),
             formatted_output: "done".into(),
@@ -313,6 +314,7 @@ fn exec_history_cell_shows_working_then_failed() {
             call_id: "call-2".into(),
             stdout: String::new(),
             stderr: "error".into(),
+            aggregated_output: "error".into(),
             exit_code: 2,
             duration: std::time::Duration::from_millis(7),
             formatted_output: "".into(),
@@ -361,6 +363,7 @@ fn exec_history_extends_previous_when_consecutive() {
             call_id: "call-a".into(),
             stdout: "one".into(),
             stderr: String::new(),
+            aggregated_output: "one".into(),
             exit_code: 0,
             duration: std::time::Duration::from_millis(5),
             formatted_output: "one".into(),
@@ -390,6 +393,7 @@ fn exec_history_extends_previous_when_consecutive() {
             call_id: "call-b".into(),
             stdout: "two".into(),
             stderr: String::new(),
+            aggregated_output: "two".into(),
             exit_code: 0,
             duration: std::time::Duration::from_millis(5),
             formatted_output: "two".into(),

codex-rs/tui/src/history_cell.rs

@@ -750,6 +750,12 @@ pub(crate) fn new_status_output(
     PlainHistoryCell { lines }
 }
 
+/// Simple one-line log entry (dim) to surface traces and diagnostics in the transcript.
+pub(crate) fn new_log_line(message: String) -> TranscriptOnlyHistoryCell {
+    let lines: Vec<Line<'static>> = vec![Line::from(""), Line::from(message).dim()];
+    TranscriptOnlyHistoryCell { lines }
+}
+
 /// Render a summary of configured MCP servers from the current `Config`.
 pub(crate) fn empty_mcp_output() -> PlainHistoryCell {
     let lines: Vec<Line<'static>> = vec![

codex-rs/tui/src/lib.rs

@@ -124,6 +124,7 @@ pub async fn run_main(
         config_profile: cli.config_profile.clone(),
         codex_linux_sandbox_exe,
         base_instructions: None,
+        include_subagent_tool: None,
         include_plan_tool: Some(true),
         include_apply_patch_tool: None,
         disable_response_storage: cli.oss.then_some(true),

codex-rs/tui/tests/fixtures/ideal-binary-response.txt

@@ -9,7 +9,7 @@ codex
 I’m going to scan the workspace and Cargo manifests to see build profiles and
 dependencies that impact binary size. Then I’ll summarize the main causes.
 
->_
+_
   ✓ ls -la
   └ total 6696
     drwxr-xr-x@ 39 easong  staff     1248 Aug  9 08:49 .
@@ -205,4 +205,4 @@ assertions—outputs are much larger than cargo build --release.
 
 If you want, I can outline targeted trims (e.g., strip = "debuginfo", opt-level
 = "z", panic abort, tighter tokio/reqwest features) and estimate impact per
-binary.
+binary.