codex: move unloaded thread writes into store (#18361)

- Migrates unloaded `thread/name/set` and `thread/memoryModeSet`
app-server writes behind the generic
`ThreadStore::update_thread_metadata` API rather than adding one-off
store methods for setting thread name or memory mode.
- Implements the local ThreadStore metadata patch path for thread name
and memory mode, including rollout append, legacy name index updates,
SessionMeta validation/update, SQLite reconciliation, and re-reading the
stored thread.
- Adds focused local thread-store unit coverage plus app-server
integration coverage for the migrated unloaded write paths.

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

@@ -7,7 +7,6 @@ use crate::ListThreadsParams;
 use crate::LoadThreadHistoryParams;
 use crate::ReadThreadParams;
 use crate::ResumeThreadRecorderParams;
-use crate::SetThreadNameParams;
 use crate::StoredThread;
 use crate::StoredThreadHistory;
 use crate::ThreadPage;
@@ -45,9 +44,6 @@ pub trait ThreadStore: Send + Sync {
     /// Lists stored threads matching the supplied filters.
     async fn list_threads(&self, params: ListThreadsParams) -> ThreadStoreResult<ThreadPage>;
 
-    /// Sets a user-facing thread name.
-    async fn set_thread_name(&self, params: SetThreadNameParams) -> ThreadStoreResult<()>;
-
     /// Applies a mutable metadata patch and returns the updated thread.
     async fn update_thread_metadata(
         &self,