AttemptPlan

What an attempt at a queue entry does to its thread (Stage 5 rule 4, design 4.55), decided after RunQueue.recordAttempt recorded the attempt's RunId and before the attempt touches the thread:

• Start: none of the entry's runs committed - its input was never admitted, an earlier attempt having died before its first commit - so the attempt admits it: run (or the typed agent's run) for a start, resume for a resume.
• Recover: the attempt recovers the thread - its entry's admitted run is the thread's latest and incomplete (Running), so a worker died mid-run; or the entry is a queued recover, whose attempts recover the thread until one of them commits (the owner's explicit transfer of the thread's recovery to the queue).
• Close: the entry's input was admitted and the thread has moved on - its run reached rest, or the thread moved on through a direct recover, which applied the input once - so the attempt closes the entry with outcome, running nothing. That includes an admitted entry (QueueEntry.admitted) whose checkpoints the lookup no longer finds: a direct run's blocked turn retracted them (Commit.retractTurn), so the input must not run again.