Errors

Error responses carry a message, a machine-readable code, and sometimes details:

json

{ "error": "Validation error", "code": "VALIDATION_ERROR", "details": {} }

Status	Code	Meaning
400	BAD_REQUEST	The request is malformed or the state does not allow it.
400	VALIDATION_ERROR	The body failed schema validation. details carries the field errors.
401	UNAUTHORIZED	Missing, unknown, revoked or expired key.
403	FORBIDDEN	Authenticated but not allowed, including API keys on session-only endpoints.
404	NOT_FOUND	No such resource, or no access to it. Kosuke does not distinguish the two.
402	CREDIT_LIMIT_REACHED	Out of free credits. details carries usedUsd and limitUsd.
409	JOB_IN_PROGRESS	A job is already running in this session and could not be steered.
409	JOB_STOPPED	The run you targeted was stopped on purpose.
429	TOO_MANY_REQUESTS	Rate limited.
503	SERVICE_UNAVAILABLE	Transient. Retrying the same request is correct.
500	SERVER_ERROR	Unexpected.

A presented but invalid key is terminal. It will not fall through to a session cookie that happens to be on the same request.