Move message history out of core (#21278)

## Why

Message history was implemented inside `codex-core` and surfaced through
core protocol ops and `SessionConfiguredEvent` fields even though the
current consumer is TUI-local prompt recall. That made core own UI
history persistence and exposed `history_log_id` / `history_entry_count`
through surfaces that app-server and other clients do not need.

This change moves message history persistence out of core and keeps the
recall plumbing local to the TUI.

## What changed

- Added a new `codex-message-history` crate for appending, looking up,
trimming, and reading metadata from `history.jsonl`.
- Removed core protocol history ops/events: `AddToHistory`,
`GetHistoryEntryRequest`, and `GetHistoryEntryResponse`.
- Removed `history_log_id` and `history_entry_count` from
`SessionConfiguredEvent` and updated exec/MCP/test fixtures accordingly.
- Updated the TUI to dispatch local app events for message-history
append/lookup and keep its persistent-history metadata in TUI session
state.

## Validation

- `cargo test -p codex-message-history -p codex-protocol`
- `cargo test -p codex-exec event_processor_with_json_output`
- `cargo test -p codex-mcp-server outgoing_message`
- `cargo test -p codex-tui`
- `just fix -p codex-message-history -p codex-protocol -p codex-core -p
codex-tui -p codex-exec -p codex-mcp-server`

codex-rs/protocol/src/lib.rs

@@ -16,7 +16,6 @@ pub mod exec_output;
 pub mod items;
 pub mod mcp;
 pub mod memory_citation;
-pub mod message_history;
 pub mod models;
 pub mod network_policy;
 pub mod num_format;

codex-rs/protocol/src/message_history.rs

@@ -1,11 +0,0 @@
-use schemars::JsonSchema;
-use serde::Deserialize;
-use serde::Serialize;
-use ts_rs::TS;
-
-#[derive(Serialize, Deserialize, Debug, Clone, JsonSchema, TS)]
-pub struct HistoryEntry {
-    pub conversation_id: String,
-    pub ts: u64,
-    pub text: String,
-}

codex-rs/protocol/src/protocol.rs

@@ -34,7 +34,6 @@ use crate::mcp::Resource as McpResource;
 use crate::mcp::ResourceTemplate as McpResourceTemplate;
 use crate::mcp::Tool as McpTool;
 use crate::memory_citation::MemoryCitation;
-use crate::message_history::HistoryEntry;
 use crate::models::ActivePermissionProfile;
 use crate::models::BaseInstructions;
 use crate::models::ContentItem;
@@ -723,18 +722,6 @@ pub enum Op {
         response: DynamicToolResponse,
     },
 
-    /// Append an entry to the persistent cross-session message history.
-    ///
-    /// Note the entry is not guaranteed to be logged if the user has
-    /// history disabled, it matches the list of "sensitive" patterns, etc.
-    AddToHistory {
-        /// The message text to be stored.
-        text: String,
-    },
-
-    /// Request a single history entry identified by `log_id` + `offset`.
-    GetHistoryEntryRequest { offset: usize, log_id: u64 },
-
     /// Request the list of MCP tools available across all configured servers.
     /// Reply is delivered via `EventMsg::McpListToolsResponse`.
     ListMcpTools,
@@ -875,8 +862,6 @@ impl Op {
             Self::UserInputAnswer { .. } => "user_input_answer",
             Self::RequestPermissionsResponse { .. } => "request_permissions_response",
             Self::DynamicToolResponse { .. } => "dynamic_tool_response",
-            Self::AddToHistory { .. } => "add_to_history",
-            Self::GetHistoryEntryRequest { .. } => "get_history_entry_request",
             Self::ListMcpTools => "list_mcp_tools",
             Self::RefreshMcpServers { .. } => "refresh_mcp_servers",
             Self::ReloadUserConfig => "reload_user_config",
@@ -1421,9 +1406,6 @@ pub enum EventMsg {
 
     TurnDiff(TurnDiffEvent),
 
-    /// Response to GetHistoryEntryRequest.
-    GetHistoryEntryResponse(GetHistoryEntryResponseEvent),
-
     /// List of MCP tools available to the agent.
     McpListToolsResponse(McpListToolsResponseEvent),
 
@@ -3265,15 +3247,6 @@ pub struct TurnDiffEvent {
     pub unified_diff: String,
 }
 
-#[derive(Debug, Clone, Deserialize, Serialize, JsonSchema, TS)]
-pub struct GetHistoryEntryResponseEvent {
-    pub offset: usize,
-    pub log_id: u64,
-    /// The entry at the requested offset, if available and parseable.
-    #[serde(skip_serializing_if = "Option::is_none")]
-    pub entry: Option<HistoryEntry>,
-}
-
 #[derive(Debug, Clone, Deserialize, Serialize, JsonSchema, TS)]
 pub struct McpListToolsResponseEvent {
     /// Fully qualified tool name -> tool definition.
@@ -3503,12 +3476,6 @@ pub struct SessionConfiguredEvent {
     #[serde(skip_serializing_if = "Option::is_none")]
     pub reasoning_effort: Option<ReasoningEffortConfig>,
 
-    /// Identifier of the history log file (inode on Unix, 0 otherwise).
-    pub history_log_id: u64,
-
-    /// Current number of entries in the history log.
-    pub history_entry_count: usize,
-
     /// Optional initial messages (as events) for resumed sessions.
     /// When present, UIs can use these to seed the history.
     #[serde(skip_serializing_if = "Option::is_none")]
@@ -3554,8 +3521,6 @@ impl<'de> Deserialize<'de> for SessionConfiguredEvent {
             active_permission_profile: Option<ActivePermissionProfile>,
             cwd: AbsolutePathBuf,
             reasoning_effort: Option<ReasoningEffortConfig>,
-            history_log_id: u64,
-            history_entry_count: usize,
             initial_messages: Option<Vec<EventMsg>>,
             network_proxy: Option<SessionNetworkProxyRuntime>,
             rollout_path: Option<PathBuf>,
@@ -3588,8 +3553,6 @@ impl<'de> Deserialize<'de> for SessionConfiguredEvent {
             active_permission_profile: wire.active_permission_profile,
             cwd: wire.cwd,
             reasoning_effort: wire.reasoning_effort,
-            history_log_id: wire.history_log_id,
-            history_entry_count: wire.history_entry_count,
             initial_messages: wire.initial_messages,
             network_proxy: wire.network_proxy,
             rollout_path: wire.rollout_path,
@@ -5319,8 +5282,6 @@ mod tests {
                 active_permission_profile: None,
                 cwd: test_path_buf("/home/user/project").abs(),
                 reasoning_effort: Some(ReasoningEffortConfig::default()),
-                history_log_id: 0,
-                history_entry_count: 0,
                 initial_messages: None,
                 network_proxy: None,
                 rollout_path: Some(rollout_file.path().to_path_buf()),
@@ -5340,8 +5301,6 @@ mod tests {
                 "permission_profile": permission_profile,
                 "cwd": test_path_buf("/home/user/project"),
                 "reasoning_effort": "medium",
-                "history_log_id": 0,
-                "history_entry_count": 0,
                 "rollout_path": format!("{}", rollout_file.path().display()),
             }
         });
@@ -5362,8 +5321,6 @@ mod tests {
                 "type": "read-only"
             },
             "cwd": cwd,
-            "history_log_id": 0,
-            "history_entry_count": 0,
         });
 
         let event: SessionConfiguredEvent = serde_json::from_value(value)?;