Migrate fork and resume reads to thread store (#18900)

- Route cold thread/resume and thread/fork source loading through
ThreadStore reads instead of direct rollout path operations
- Keep lookups that explicitly specify a rollout-path using the local
thread store methods but return an invalid-request error for remote
ThreadStore configurations
- Add some additional unit tests for code path coverage

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

@@ -7,6 +7,7 @@ use crate::ArchiveThreadParams;
 use crate::CreateThreadParams;
 use crate::ListThreadsParams;
 use crate::LoadThreadHistoryParams;
+use crate::ReadThreadByRolloutPathParams;
 use crate::ReadThreadParams;
 use crate::ResumeThreadParams;
 use crate::StoredThread;
@@ -18,8 +19,7 @@ use crate::UpdateThreadMetadataParams;
 /// Storage-neutral thread persistence boundary.
 #[async_trait]
 pub trait ThreadStore: Any + Send + Sync {
-    /// Return this store as [`Any`] so callers at API boundaries can reject requests that only
-    /// make sense for a concrete store implementation.
+    /// Return this store as [`Any`] for implementation-owned escape hatches.
     fn as_any(&self) -> &dyn Any;
 
     /// Creates a new live thread.
@@ -56,6 +56,14 @@ pub trait ThreadStore: Any + Send + Sync {
     /// Reads a thread summary and optionally its persisted history.
     async fn read_thread(&self, params: ReadThreadParams) -> ThreadStoreResult<StoredThread>;
 
+    /// Reads a rollout-backed thread by path when the store supports path-addressed lookups.
+    ///
+    /// Deprecated: new callers should use [`ThreadStore::read_thread`] instead.
+    async fn read_thread_by_rollout_path(
+        &self,
+        params: ReadThreadByRolloutPathParams,
+    ) -> ThreadStoreResult<StoredThread>;
+
     /// Lists stored threads matching the supplied filters.
     async fn list_threads(&self, params: ListThreadsParams) -> ThreadStoreResult<ThreadPage>;