Main Sequence AI Provider Errors

The Main Sequence AI assistant transport consumes model-provider failures through the standard assistant UI message-stream error frame:

{"type": "error", "errorText": "provider-supplied failure message"}

errorText is the canonical user-facing field and takes precedence over the legacy error, message, and error_detail fallbacks. The transport reports that value through its normal error callback so chat surfaces display the reason returned by the provider.

Command Center does not map particular providers, HTTP status codes, billing states, authentication failures, or rate-limit variants to custom messages. The Agent runtime owns extraction of the provider message and must not include the raw provider response body in this frame. When errorText is absent, Command Center retains a generic runtime-error fallback.