RspError
Structured representation of an error response returned by the magmaguy.com resource-pack hosting API. Mirrors the JSON shape used by the existing AutoHost.handleErrorResponse(...) flow.
Known error codes include: MISSING_REQUIRED_FILES, FILE_TOO_LARGE, INVALID_FILE_FORMAT, SESSION_NOT_FOUND, SERVER_UNAVAILABLE. The type field carries the broader category (e.g. validation_error).