| `AGENT_SESSION_RUN_LIMIT_EXCEEDED` | 409 | Session already reached max run count (start + 1 follow-up) | Show run-limit message and require starting a new session |
| `AGENT_RUNTIME_MODE_INVALID` | 422 | Missing or invalid `forwardedProps.runtime_mode` in run request | Show invalid-request message and retry from current page |
| `AGENT_DIVINATION_PAYLOAD_REQUIRED` | 422 | Missing required `forwardedProps.divinationPayload` in run request | Prompt user to restart casting flow and resubmit |
| `AGENT_SESSION_ID_INVALID` | 422 | Invalid session/thread id format | Show invalid-session message and force refresh history |
| `AGENT_SESSION_NOT_FOUND` | 404 | Session does not exist (including follow-up on non-existing thread) | Show session-not-found message and refresh history |
| `AGENT_AUDIO_UNSUPPORTED_FORMAT` | 400 | Audio format is not accepted by transcribe endpoint | Show format hint and ask user to retry with wav audio |
| `AGENT_AUDIO_TOO_LARGE` | 400 | Audio file exceeds transcribe size limit | Show size-limit message and ask user to shorten audio |
| `AGENT_AUDIO_EMPTY` | 400 | Uploaded audio payload is empty | Show retry hint and keep input unchanged |
| `AGENT_ASR_UNAVAILABLE` | 502 | Upstream ASR service unavailable | Show retry message and allow fallback to text input |