Allow per-turn overrides for direct-only tool namespaces (#59481)

## What changed

- Add `direct_only_tool_namespaces` to `TurnStartOptions`. Omission inherits the thread configuration; an empty list clears direct-only routing for that turn. Steering ignores the option.
- Persist explicit overrides in turn context and restore them when recovering an interrupted turn, including turns started by standalone tool output.
- Keep subsequent turns and spawned or resumed child agents on the thread's routing defaults.

## Testing

Add coverage for routing changes across turns in Responses and Responses Lite, recovery without carrying overrides into subsequent turns, and child-agent inheritance.

GitOrigin-RevId: cea1a997424572d4cd372cd15b098626904c6796

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

@@ -1141,6 +1141,7 @@ mod tests {
             RolloutItem::TurnContext(TurnContextItem {
                 turn_id: Some("turn-1".to_string()),
                 root_turn_id: None,
+                direct_only_tool_namespaces: None,
                 disabled_plugin_ids: None,
                 cwd: serde_json::from_value(serde_json::json!(cwd)).expect("absolute cwd"),
                 approval_policy,

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

@@ -742,6 +742,7 @@ fn turn_context(root: &Path, turn_id: &str) -> RolloutItem {
     RolloutItem::TurnContext(TurnContextItem {
         turn_id: Some(turn_id.to_string()),
         root_turn_id: None,
+        direct_only_tool_namespaces: None,
         disabled_plugin_ids: None,
         cwd: serde_json::from_value(serde_json::json!(root)).expect("absolute cwd"),
         approval_policy: AskForApproval::Never,

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

@@ -2217,6 +2217,7 @@ async fn migration_compacts_subagent_prefix_and_does_not_project_it() {
             RolloutItem::TurnContext(TurnContextItem {
                 turn_id: Some("child-turn".to_string()),
                 root_turn_id: None,
+                direct_only_tool_namespaces: None,
                 disabled_plugin_ids: None,
                 cwd: serde_json::from_value(json!(home.path())).expect("absolute cwd"),
                 approval_policy: AskForApproval::Never,