ReadonlyreasonAn optional machine-readable reason, rendered into the response body alongside the message. DECLARED HERE rather than sniffed structurally at the mapper so the channel is part of the contract a subclass opts into, and so the mapper needs no import of any subclass to render it (see the header for why that import must not exist).
Readonlycode: "IDEMPOTENT_START_PENDING"ReadonlypendingSince: numberEpoch ms of the claim, so a caller can reason about how long.
ReadonlyrunId: stringReadonlystatusThe response status. 4xx/5xx only — see doErrorResponse.
The key's run is executing right now. 503 for the same reason every operator-transient refusal in this package is: the condition is real, it is nobody's mistake, and it clears on its own — so a client that honours retry semantics converges instead of giving up.