Persist loaded threads before managed daemon shutdown (#44283)

## Why

Loaded threads, including idle threads whose rollout files are still deferred, need to survive a managed daemon restart. Shutdown must also remain forceable when rollout I/O is blocked.

## What changed

- Add a hidden `--managed-daemon` option for app-server Unix socket transports. After active turns and admitted requests drain, save loaded persistent root threads before exiting.
- Skip ephemeral threads, non-root agent threads, and threads pending unload. Log persistence failures and continue saving other threads.
- Apply shutdown admission checks to thread and turn settings updates, thread deletion, and archiving.
- Keep force signals and daemon shutdown requests responsive during persistence. Return `AppServerExit::Forced` so executables can exit without waiting for runtime teardown.

## Testing

Add integration coverage for resuming active and idle threads after restart, forcing shutdown during active work, and forcing shutdown with a blocked rollout writer. Extend shutdown rejection coverage to deletion and settings updates.

GitOrigin-RevId: 4344e97d39f9f80c5d84c41c17300fd6aa99b4cc

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

@@ -759,6 +759,10 @@ impl MessageProcessor {
         self.thread_processor.thread_created_receiver()
     }
 
+    pub(crate) async fn persist_daemon_threads(&self) {
+        self.thread_processor.persist_daemon_threads().await
+    }
+
     pub(crate) async fn send_initialize_notifications_to_connection(
         &self,
         connection_id: ConnectionId,
@@ -951,7 +955,11 @@ impl MessageProcessor {
             | ClientRequest::ThreadFork { .. }
             | ClientRequest::ThreadResume { .. }
             | ClientRequest::ThreadRollback { .. }
-            | ClientRequest::ThreadRevert { .. } => (Some(self.turn_admission.admit()?), false),
+            | ClientRequest::ThreadRevert { .. }
+            | ClientRequest::ThreadSettingsUpdate { .. }
+            | ClientRequest::TurnSettingsUpdate { .. }
+            | ClientRequest::ThreadDelete { .. }
+            | ClientRequest::ThreadArchive { .. } => (Some(self.turn_admission.admit()?), false),
             ClientRequest::TurnStart { .. }
             | ClientRequest::TurnSteer { .. }
             | ClientRequest::ReviewStart { .. }