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/app-server-protocol/schema/json/v2/GuardianWarningNotification.json

@@ -0,0 +1,19 @@
+{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "properties": {
+    "message": {
+      "description": "Concise guardian warning message for the user.",
+      "type": "string"
+    },
+    "threadId": {
+      "description": "Thread target for the guardian warning.",
+      "type": "string"
+    }
+  },
+  "required": [
+    "message",
+    "threadId"
+  ],
+  "title": "GuardianWarningNotification",
+  "type": "object"
+}