A 503 busy says whether the cell could not confirm the request or could not complete it
Before, every 503 busy from /v1/sandboxes read "The cell could not confirm this in time; it may or may not have been applied.", whatever the cause. That message now comes only when the cell's log or a timeout is the reason. Any other cause, such as a sandbox's disk or its guest not answering, returns "The cell could not complete this right now; it may or may not have been applied." The status, the busy code and details.reason are unchanged. Retry with the same Idempotency-Key.