API error format and codes

Check the HTTP status and error body when an API request fails. Authentication and authorization failures return 401.

Error envelope

{"code":401,"message":"Not authenticated","result":"error"}

Field	Meaning
`code`	Numeric response code
`result`	Error marker where included by the response wrapper
`message`	Human-readable explanation
`errors`	Validation-dependent details
`error_details`	Additional validation details, including bad values where provided
`bad_fields`	Resource-authorization-dependent field details

Optional details vary by operation. Do not assume every error contains every field.

Code	Meaning and action
400	Invalid arguments or rejected configuration; correct the reported fields
401	Authentication or permission denied; check credential, context, expiry and grants
404	Resource or authorized parent is unavailable; check the resource and context
409	Conflict, including domain or configuration conflicts; inspect the operation's message
412	Version precondition failed; read, reconcile and retry with the current version
500	Server error; retry as appropriate and contact your account manager if it persists
503	Operation temporarily unavailable; inspect the error message before retrying

These codes are operation-dependent. See versions and concurrency. Do not substitute 403 for the API's 401 authentication response.

TODO(verify): Confirm whether a stable machine-readable error identifier exists beyond numeric code and operation-specific validation details.