[codex] Move thread naming to app server (#21260)

## Why

Thread names are app-server metadata now, backed by the thread store and
sqlite state database. Keeping a core `SetThreadName` op plus a rollout
`thread_name_updated` event made rename persistence live in the wrong
layer and required historical replay support for an event that new
app-server flows should not write.

## What changed

- Removed `Op::SetThreadName` and `EventMsg::ThreadNameUpdated` from the
core protocol and deleted the core handler path that appended rename
events to rollouts.
- Updated app-server `thread/name/set` so both loaded and unloaded
threads write through thread-store metadata and app-server emits
`thread/name/updated` notifications.
- Updated local thread-store name metadata updates to write sqlite title
metadata and the legacy thread-name index without appending rollout
events.
- Removed state extraction and rollout handling for the deleted
thread-name event.

## Validation

- `cargo test -p codex-app-server thread_name_updated_broadcasts`
- `cargo test -p codex-app-server
thread_name_set_is_reflected_in_read_list_and_resume`
- `cargo test -p codex-thread-store
update_thread_metadata_sets_name_on_active_rollout_and_indexes_name`
- `cargo test -p codex-state`
- `cargo check -p codex-mcp-server -p codex-rollout-trace`
- `just fix -p codex-app-server -p codex-thread-store -p codex-state -p
codex-mcp-server -p codex-rollout-trace`

## Docs

No external documentation update is expected for this internal ownership
change.

codex-rs/state/src/extract.rs

@@ -33,9 +33,7 @@ pub fn apply_rollout_item(
 pub fn rollout_item_affects_thread_metadata(item: &RolloutItem) -> bool {
     match item {
         RolloutItem::SessionMeta(_) | RolloutItem::TurnContext(_) => true,
-        RolloutItem::EventMsg(
-            EventMsg::TokenCount(_) | EventMsg::UserMessage(_) | EventMsg::ThreadNameUpdated(_),
-        ) => true,
+        RolloutItem::EventMsg(EventMsg::TokenCount(_) | EventMsg::UserMessage(_)) => true,
         RolloutItem::EventMsg(_) | RolloutItem::ResponseItem(_) | RolloutItem::Compacted(_) => {
             false
         }
@@ -97,13 +95,6 @@ fn apply_event_msg(metadata: &mut ThreadMetadata, event: &EventMsg) {
                 }
             }
         }
-        EventMsg::ThreadNameUpdated(updated) => {
-            if let Some(title) = updated.thread_name.as_deref()
-                && !title.trim().is_empty()
-            {
-                metadata.title = title.trim().to_string();
-            }
-        }
         _ => {}
     }
 }
@@ -159,7 +150,6 @@ mod tests {
     use codex_protocol::protocol::SessionMeta;
     use codex_protocol::protocol::SessionMetaLine;
     use codex_protocol::protocol::SessionSource;
-    use codex_protocol::protocol::ThreadNameUpdatedEvent;
     use codex_protocol::protocol::TurnContextItem;
     use codex_protocol::protocol::USER_MESSAGE_BEGIN;
     use codex_protocol::protocol::UserMessageEvent;
@@ -205,25 +195,6 @@ mod tests {
         assert_eq!(metadata.title, "actual user request");
     }
 
-    #[test]
-    fn thread_name_update_replaces_title_without_changing_first_user_message() {
-        let mut metadata = metadata_for_test();
-        metadata.title = "actual user request".to_string();
-        metadata.first_user_message = Some("actual user request".to_string());
-        let item = RolloutItem::EventMsg(EventMsg::ThreadNameUpdated(ThreadNameUpdatedEvent {
-            thread_id: metadata.id,
-            thread_name: Some("saved-session".to_string()),
-        }));
-
-        apply_rollout_item(&mut metadata, &item, "test-provider");
-
-        assert_eq!(
-            metadata.first_user_message.as_deref(),
-            Some("actual user request")
-        );
-        assert_eq!(metadata.title, "saved-session");
-    }
-
     #[test]
     fn event_msg_image_only_user_message_sets_image_placeholder_preview() {
         let mut metadata = metadata_for_test();