Fields read as error codes.
Message when there is neither a payload message nor a fallback.
Fields read as an HTTP status, first match wins.
Provider name in messages built from a bare code, such as "Codex error (500)".
OptionalnestedFields of a nested error object, read after the top-level ones.
Codes, besides the shared ones, that mean a rate limit, missing authentication or not found.
Codes, besides HTTP 503, that make a generic structured error retryable.
Message pattern that turns a not-found error into SESSION_INVALID.
Classifies a message when the payload carries no structured code.
Where and how one backend reports structured errors.