feat(auto-review) short-circuit (#18890)

## Summary
Short circuit the convo if auto-review hits too many denials

## Testing
- [x] Added unit tests

---------

Co-authored-by: Codex <noreply@openai.com>

codex-rs/protocol/src/protocol.rs

@@ -1441,6 +1441,9 @@ pub enum EventMsg {
     /// indicates the turn continued but the user should still be notified.
     Warning(WarningEvent),
 
+    /// Warning issued by the guardian automatic approval reviewer.
+    GuardianWarning(WarningEvent),
+
     /// Realtime conversation lifecycle start event.
     RealtimeConversationStarted(RealtimeConversationStartedEvent),