Run one stage function. attempt is the attempt runner's (P1b) — present when the stage runs under a retry
policy, a timeoutMs or a run deadline: the scope hands it out ($attempt()) and is fenced to it, and the
race below is against ITS signal (the run's, composed with the attempt's cap). Without one, the race is
against the run's signal, as it always was.
Run one stage function.
attemptis the attempt runner's (P1b) — present when the stage runs under a retry policy, atimeoutMsor a run deadline: the scope hands it out ($attempt()) and is fenced to it, and the race below is against ITS signal (the run's, composed with the attempt's cap). Without one, the race is against the run's signal, as it always was.