Allow searching persisted attached threads (#60574)

## Why

Title and content searches exclude attached threads, preventing clients from finding their saved conversations alongside ordinary threads.

## What changed

- Add `includeAttachedThreads` to `thread/list` and `thread/search`. For `thread/list`, require a non-empty `searchTerm` and preserve the usual provider and source filters.
- Expose `attachedToThreadId` on thread responses to identify the owning parent independently of fork and subagent lineage.
- Support inclusive searches through SQLite and filesystem fallback, repairing missing database entries with saved thread names during title searches.

## Testing

Add regression coverage for opt-in title and content searches, attached-parent metadata after restart, default search filters, filesystem searches without SQLite, and discovery and repair of unindexed title matches.

GitOrigin-RevId: ac12ec3c730ad7f1722bdf8e21600d17f12017f0

codex-rs/exec/src/lib.rs

@@ -2007,6 +2007,7 @@ async fn resolve_resume_thread_id(
                 ClientRequest::ThreadList {
                     request_id: RequestId::Integer(0),
                     params: ThreadListParams {
+                        include_attached_threads: false,
                         current_account_only: true,
                         excluded_thread_ids: None,
                         attached_to_thread_id: None,
@@ -2096,6 +2097,7 @@ async fn resolve_resume_thread_id(
             ClientRequest::ThreadList {
                 request_id: RequestId::Integer(0),
                 params: ThreadListParams {
+                    include_attached_threads: false,
                     current_account_only: false,
                     excluded_thread_ids: None,
                     attached_to_thread_id: None,

codex-rs/exec/src/lib_tests.rs

@@ -358,6 +358,7 @@ fn turn_items_for_thread_returns_matching_turn_items() {
         extra: None,
         session_id: "thread-1".to_string(),
         forked_from_id: None,
+        attached_to_thread_id: None,
         parent_thread_id: None,
         preview: String::new(),
         ephemeral: false,
@@ -871,6 +872,7 @@ fn sample_thread_start_response() -> ThreadStartResponse {
             extra: None,
             session_id: "67e55044-10b1-426f-9247-bb680e5fe0c7".to_string(),
             forked_from_id: None,
+            attached_to_thread_id: None,
             parent_thread_id: None,
             preview: String::new(),
             ephemeral: false,