app-server: Emit thread archive/unarchive notifications (#12030)

* Add v2 server notifications `thread/archived` and `thread/unarchived`
with a `threadId` payload.
* Wire new events into `thread/archive` and `thread/unarchive` success
paths.
* Update app-server protocol/schema/docs accordingly.

Testing:
- Updated archive/unarchive end-to-end tests to verify both
notifications are emitted with the expected thread id payload.

codex-rs/app-server/tests/suite/v2/thread_unarchive.rs

@@ -10,11 +10,13 @@ use codex_app_server_protocol::ThreadStartParams;
 use codex_app_server_protocol::ThreadStartResponse;
 use codex_app_server_protocol::ThreadUnarchiveParams;
 use codex_app_server_protocol::ThreadUnarchiveResponse;
+use codex_app_server_protocol::ThreadUnarchivedNotification;
 use codex_app_server_protocol::TurnStartParams;
 use codex_app_server_protocol::TurnStartResponse;
 use codex_app_server_protocol::UserInput;
 use codex_core::find_archived_thread_path_by_id_str;
 use codex_core::find_thread_path_by_id_str;
+use pretty_assertions::assert_eq;
 use std::fs::FileTimes;
 use std::fs::OpenOptions;
 use std::path::Path;
@@ -120,6 +122,17 @@ async fn thread_unarchive_moves_rollout_back_into_sessions_directory() -> Result
     let ThreadUnarchiveResponse {
         thread: unarchived_thread,
     } = to_response::<ThreadUnarchiveResponse>(unarchive_resp)?;
+    let unarchive_notification = timeout(
+        DEFAULT_READ_TIMEOUT,
+        mcp.read_stream_until_notification_message("thread/unarchived"),
+    )
+    .await??;
+    let unarchived_notification: ThreadUnarchivedNotification = serde_json::from_value(
+        unarchive_notification
+            .params
+            .expect("thread/unarchived notification params"),
+    )?;
+    assert_eq!(unarchived_notification.thread_id, thread.id);
     assert!(
         unarchived_thread.updated_at > old_timestamp,
         "expected updated_at to be bumped on unarchive"