Document the site_unreachable MCP error

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

Author: kev1n

mcp-server.mdx

@@ -524,6 +524,7 @@ Tool failures come back as MCP tool errors with a short machine-readable prefix:
 | `provider_rejected_request` | The upstream rejected this request; adjust it before retrying | No |
 | `provider_rate_limited` | The upstream rate-limited the request; retry later | No |
 | `provider_timeout` | Every available route ended in an upstream timeout | No (released) |
+| `site_unreachable` | Every route timed out on this site within the last 24 hours, so the call was refused before it ran; the message says when AnyAPI will try the site again | No |
 | `provider_transport_error` | Every available route ended in a network failure | No (released) |
 | `provider_failure` | Every available route ended in an upstream service failure | No (released) |
 | `malformed_upstream_response` | The upstream response could not be safely normalized | No (released) |