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/protocol/src/protocol.rs

@@ -3634,6 +3634,10 @@ pub struct TurnContextItem {
     /// Root turn that owns this turn's attribution, retained across recovery.
     #[serde(default, skip_serializing_if = "Option::is_none")]
     pub root_turn_id: Option<String>,
+    /// Explicit routing for this turn. An empty list clears the thread's direct namespaces.
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    #[ts(optional)]
+    pub direct_only_tool_namespaces: Option<Vec<String>>,
     /// Plugin selection captured for this turn. Absent in older histories.
     #[serde(default, skip_serializing_if = "Option::is_none")]
     #[ts(optional)]
@@ -6594,6 +6598,7 @@ mod tests {
         let item = TurnContextItem {
             turn_id: None,
             root_turn_id: None,
+            direct_only_tool_namespaces: None,
             disabled_plugin_ids: None,
             cwd: test_path_buf("/tmp").abs(),
             approval_policy: AskForApproval::Never,