Add turn error lifecycle contributor (#24916)

Summary
- Add TurnErrorInput and TurnLifecycleContributor::on_turn_error to the
extension API.
- Emit the turn-error lifecycle from core turn error paths, including
usage limit failures.
- Add direct lifecycle coverage for the emitted error facts and stores.

Tests
- just fmt
- git diff --check
- Not run: full tests or clippy (per instructions)

codex-rs/ext/extension-api/src/contributors.rs

@@ -26,6 +26,7 @@ pub use tool_lifecycle::ToolFinishInput;
 pub use tool_lifecycle::ToolLifecycleFuture;
 pub use tool_lifecycle::ToolStartInput;
 pub use turn_lifecycle::TurnAbortInput;
+pub use turn_lifecycle::TurnErrorInput;
 pub use turn_lifecycle::TurnStartInput;
 pub use turn_lifecycle::TurnStopInput;
 
@@ -79,6 +80,9 @@ pub trait TurnLifecycleContributor: Send + Sync {
 
     /// Called after the host aborts a running turn.
     async fn on_turn_abort(&self, _input: TurnAbortInput<'_>) {}
+
+    /// Called when the host observes an error for a running turn.
+    async fn on_turn_error(&self, _input: TurnErrorInput<'_>) {}
 }
 
 /// Contributor for host-owned configuration changes.