[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/app-server/tests/suite/v2/thread_name_websocket.rs

@@ -22,11 +22,7 @@ use codex_app_server_protocol::ThreadResumeResponse;
 use codex_app_server_protocol::ThreadSetNameParams;
 use codex_app_server_protocol::ThreadSetNameResponse;
 use codex_core::find_thread_name_by_id;
-use codex_core::find_thread_path_by_id_str;
 use codex_protocol::ThreadId;
-use codex_protocol::protocol::EventMsg;
-use codex_protocol::protocol::RolloutItem;
-use codex_protocol::protocol::RolloutLine;
 use pretty_assertions::assert_eq;
 use std::path::Path;
 use tempfile::TempDir;
@@ -85,10 +81,6 @@ async fn thread_name_updated_broadcasts_for_loaded_threads() -> Result<()> {
             read_notification_for_method(&mut ws2, "thread/name/updated").await?;
         assert_thread_name_updated(ws2_notification, &conversation_id, renamed)?;
         assert_legacy_thread_name(codex_home.path(), &conversation_id, renamed).await?;
-        assert_eq!(
-            thread_name_update_rollout_count(codex_home.path(), &conversation_id).await?,
-            1
-        );
 
         assert_no_message(&mut ws1, Duration::from_millis(250)).await?;
         assert_no_message(&mut ws2, Duration::from_millis(250)).await?;
@@ -141,10 +133,6 @@ async fn thread_name_updated_broadcasts_for_not_loaded_threads() -> Result<()> {
             read_notification_for_method(&mut ws2, "thread/name/updated").await?;
         assert_thread_name_updated(ws2_notification, &conversation_id, renamed)?;
         assert_legacy_thread_name(codex_home.path(), &conversation_id, renamed).await?;
-        assert_eq!(
-            thread_name_update_rollout_count(codex_home.path(), &conversation_id).await?,
-            1
-        );
 
         assert_no_message(&mut ws1, Duration::from_millis(250)).await?;
         assert_no_message(&mut ws2, Duration::from_millis(250)).await?;
@@ -206,24 +194,3 @@ async fn assert_legacy_thread_name(
     );
     Ok(())
 }
-
-async fn thread_name_update_rollout_count(
-    codex_home: &Path,
-    conversation_id: &str,
-) -> Result<usize> {
-    let rollout_path =
-        find_thread_path_by_id_str(codex_home, conversation_id, /*state_db_ctx*/ None)
-            .await?
-            .context("rollout path")?;
-    let contents = tokio::fs::read_to_string(rollout_path).await?;
-    Ok(contents
-        .lines()
-        .filter_map(|line| serde_json::from_str::<RolloutLine>(line).ok())
-        .filter(|line| {
-            matches!(
-                line.item,
-                RolloutItem::EventMsg(EventMsg::ThreadNameUpdated(_))
-            )
-        })
-        .count())
-}