What it means
frozen; plain GET on the agent WebSocket path.
How to handle it
Connect to the agent WebSocket endpoint with a WebSocket client that performs the HTTP upgrade.
Wire contract
| Code | upgrade_required |
|---|---|
| Class | invalid_request |
| HTTP status | 426 |
| Meta keys | None |
| Raised | Yes |
The response uses the standard {"error": {…}} envelope. Branch on error.code, not the human-readable message. Preserve request_id when reporting a failure.