A job that fails because its machine ran out of disk says so in its reason

When a job's machine runs out of disk, the error is often never written to the job's log, because the log is on the same full disk. Such a job's reason was the log's last error, for example error: build failed, waiting for other jobs to finish.... The job's log now ends with a line that says the machine ran out of disk (error: No space left on device: ...), and its reason names that line.