Unify thread metadata updates above store (#22236)

- make ThreadStore::update_thread_metadata accept a broad range of
metadata patches
- keep ThreadStore::append_items as raw canonical history append (no
metadata side effects)
- in the local store, write these metadata updates to a combination of
sqlite and rollout jsonl files for backwards-compat. It special cases
which fields need to go into jsonl vs sqlite vs whatever, confining the
awkwardness to just this implementation
- in remote stores we can simply persist the metadata directly to a
database, no special casing required.
- move the "implicit metadata updates triggered by appending rollout
items" from the RolloutRecorder (which is local-threadstore-specific) to
the LiveThread layer above the ThreadStore, inside of a private helper
utility called ThreadMetadataSync. LiveThread calls ThreadStore
append_items and update_metadata separately.
- Add a generic update metadata method to ThreadManager that works on
both live threads and "cold" threads
- Call that ThreadManager method from app server code, so app server
doesn't need to worry about whether the thread is live or not

codex-rs/thread-store/src/local/read_thread.rs

@@ -273,7 +273,8 @@ async fn stored_thread_from_sqlite_metadata(
         None => find_thread_name_by_id(store.config.codex_home.as_path(), &metadata.id)
             .await
             .ok()
-            .flatten(),
+            .flatten()
+            .filter(|title| !title.trim().is_empty()),
     };
     let session_meta = read_session_meta_line(metadata.rollout_path.as_path())
         .await