Add interrupted turn recovery (#38303)

## What changed

- Add `RecoverTurnRequest` and `CodexThread::recover_turn_if_idle` to resume an interrupted regular turn with its existing turn ID and updated thread settings.
- Treat recovery separately from automatic idle work so it can resume in Plan mode without injecting an empty user message.
- Reject recovery while another turn is active without applying settings or queuing input.

## Testing

- Cover successful Plan-mode recovery, turn ID preservation, and the absence of an empty user message.
- Cover active-turn rejection and verify that it leaves settings and pending input unchanged.

GitOrigin-RevId: 2376fdc78b5d48b571633981960741ba269ab1ef

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

@@ -120,6 +120,7 @@ use codex_protocol::protocol::RawResponseItemEvent;
 use codex_protocol::protocol::SessionSource;
 use codex_protocol::protocol::SubAgentSource;
 use codex_protocol::protocol::ThreadHistoryMode;
+use codex_protocol::protocol::ThreadSettingsOverrides;
 use codex_protocol::protocol::ThreadSource;
 use codex_protocol::protocol::TurnAbortReason;
 use codex_protocol::protocol::TurnContextItem;
@@ -856,6 +857,27 @@ impl SessionIo {
         reply_rx.await.unwrap_or(Err(CodexErr::InternalAgentDied))
     }
 
+    pub(crate) async fn submit_recover_turn(
+        &self,
+        thread_settings: ThreadSettingsOverrides,
+        trace: Option<W3cTraceContext>,
+        turn_id: String,
+    ) -> CodexResult<TurnInputSubmission> {
+        let (reply_tx, reply_rx) = oneshot::channel();
+        self.submit_with_id(Submission {
+            id: turn_id,
+            op: Op::RecoverTurn {
+                thread_settings,
+                reply: reply_tx,
+            },
+            trace,
+            parent_turn_id: None,
+            root_turn_id: None,
+        })
+        .await?;
+        reply_rx.await.unwrap_or(Err(CodexErr::InternalAgentDied))
+    }
+
     pub(crate) async fn shutdown_and_wait(&self) -> CodexResult<()> {
         let session_loop_termination = self.session_loop_termination.clone();
         match self.submit(Op::Shutdown).await {