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/app-server-protocol/src/protocol/common.rs

@@ -3347,6 +3347,7 @@ mod tests {
                     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: "first prompt".to_string(),
                     ephemeral: true,
@@ -3406,6 +3407,7 @@ mod tests {
                         "extra": null,
                         "sessionId": "67e55044-10b1-426f-9247-bb680e5fe0c7",
                         "forkedFromId": null,
+                        "attachedToThreadId": null,
                         "parentThreadId": null,
                         "preview": "first prompt",
                         "ephemeral": true,

codex-rs/app-server-protocol/src/protocol/v2/tests.rs

@@ -304,6 +304,7 @@ fn thread_resume_response_round_trips_initial_turns_page() {
             extra: None,
             session_id: "thr_123".to_string(),
             forked_from_id: None,
+            attached_to_thread_id: None,
             parent_thread_id: None,
             preview: String::new(),
             ephemeral: false,

codex-rs/app-server-protocol/src/protocol/v2/thread.rs

@@ -1435,6 +1435,10 @@ pub struct ThreadSectionDeleteResponse {}
 #[serde(rename_all = "camelCase")]
 #[ts(export_to = "v2/")]
 pub struct ThreadListParams {
+    /// Include persistent threads attached to a parent when searching by title.
+    #[experimental("thread/list.includeAttachedThreads")]
+    #[serde(default, skip_serializing_if = "std::ops::Not::not")]
+    pub include_attached_threads: bool,
     /// Show local history visible to the current ChatGPT account. Defaults to false.
     #[serde(default, skip_serializing_if = "std::ops::Not::not")]
     pub current_account_only: bool,
@@ -1526,6 +1530,9 @@ pub struct ThreadListParams {
 #[serde(rename_all = "camelCase")]
 #[ts(export_to = "v2/")]
 pub struct ThreadSearchParams {
+    /// Include persistent threads attached to a parent in search results.
+    #[serde(default, skip_serializing_if = "std::ops::Not::not")]
+    pub include_attached_threads: bool,
     /// Show local history visible to the current ChatGPT account. Defaults to false.
     #[serde(default, skip_serializing_if = "std::ops::Not::not")]
     pub current_account_only: bool,

codex-rs/app-server-protocol/src/protocol/v2/thread_data.rs

@@ -218,6 +218,9 @@ pub struct Thread {
     pub session_id: String,
     /// Source thread id when this thread was created by forking another thread.
     pub forked_from_id: Option<String>,
+    /// Parent that owns this persisted attached thread, independent of fork or spawn lineage.
+    #[experimental("thread.attachedToThreadId")]
+    pub attached_to_thread_id: Option<String>,
     /// The ID of the parent thread. This will only be set if this thread is a subagent.
     pub parent_thread_id: Option<String>,
     /// Usually the first user message in the thread, if available.
@@ -305,6 +308,7 @@ struct ThreadCompatibility {
     extra: Option<ThreadExtra>,
     session_id: String,
     forked_from_id: Option<String>,
+    attached_to_thread_id: Option<String>,
     parent_thread_id: Option<String>,
     preview: String,
     ephemeral: bool,
@@ -350,6 +354,7 @@ impl<'de> Deserialize<'de> for Thread {
             extra: thread.extra,
             session_id: thread.session_id,
             forked_from_id: thread.forked_from_id,
+            attached_to_thread_id: thread.attached_to_thread_id,
             parent_thread_id: thread.parent_thread_id,
             preview: thread.preview,
             ephemeral: thread.ephemeral,