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/core/src/session/handlers.rs

@@ -460,53 +460,6 @@ pub async fn dynamic_tool_response(sess: &Arc<Session>, id: String, response: Dy
     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(
-                codex_protocol::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);
@@ -910,14 +863,6 @@ pub(super) async fn submission_loop(
                     dynamic_tool_response(&sess, id, response).await;
                     false
                 }
-                Op::AddToHistory { text } => {
-                    add_to_history(&sess, &config, text).await;
-                    false
-                }
-                Op::GetHistoryEntryRequest { offset, log_id } => {
-                    get_history_entry_request(&sess, &config, sub.id.clone(), offset, log_id).await;
-                    false
-                }
                 Op::ListMcpTools => {
                     list_mcp_tools(&sess, &config, sub.id.clone()).await;
                     false

codex-rs/core/src/session/session.rs

@@ -470,19 +470,6 @@ impl Session {
         ));
         let state_db_ctx = if config.ephemeral { None } else { state_db };
 
-        let is_subagent = session_configuration.session_source.is_non_root_agent();
-        let history_meta_fut = async {
-            if is_subagent {
-                (0, 0)
-            } else {
-                crate::message_history::history_metadata(&config).await
-            }
-        }
-        .instrument(info_span!(
-            "session_init.history_metadata",
-            otel.name = "session_init.history_metadata",
-            session_init.is_subagent = is_subagent,
-        ));
         let auth_manager_clone = Arc::clone(&auth_manager);
         let config_for_mcp = Arc::clone(&config);
         let mcp_manager_for_mcp = Arc::clone(&mcp_manager);
@@ -505,11 +492,8 @@ impl Session {
         ));
 
         // Join all independent futures.
-        let (
-            thread_persistence_result,
-            (history_log_id, history_entry_count),
-            (auth, mcp_servers, auth_statuses),
-        ) = tokio::join!(thread_persistence_fut, history_meta_fut, auth_and_mcp_fut);
+        let (thread_persistence_result, (auth, mcp_servers, auth_statuses)) =
+            tokio::join!(thread_persistence_fut, auth_and_mcp_fut);
 
         let mut live_thread_init =
             LiveThreadInitGuard::new(thread_persistence_result.map_err(|e| {
@@ -920,8 +904,6 @@ impl Session {
                     active_permission_profile: session_configuration.active_permission_profile(),
                     cwd: session_configuration.cwd.clone(),
                     reasoning_effort: session_configuration.collaboration_mode.reasoning_effort(),
-                    history_log_id,
-                    history_entry_count,
                     initial_messages,
                     network_proxy: session_network_proxy.filter(|_| {
                         Self::managed_network_proxy_active_for_permission_profile(

codex-rs/core/src/session/turn.rs

@@ -1509,7 +1509,6 @@ pub(super) fn realtime_text_for_event(msg: &EventMsg) -> Option<String> {
         | EventMsg::DeprecationNotice(_)
         | EventMsg::StreamError(_)
         | EventMsg::TurnDiff(_)
-        | EventMsg::GetHistoryEntryResponse(_)
         | EventMsg::McpListToolsResponse(_)
         | EventMsg::RealtimeConversationListVoicesResponse(_)
         | EventMsg::SkillsUpdateAvailable