Ask for effects on a task

The assignee asks for one or more effects (reply, forward, label, snooze, resolve, note, request). The delegation's level decides the kinds allowed and the grants cap them: inside the grants at guarded_send or operate (and the inward kinds at triage) the effects run at once with their receipts; at draft they wait for the owner's approval; a failed grant escalates to the owner; a kind the level does not allow is refused. The owner's own request runs at once. The same idempotency key answers the first plan again. Requires assistant:write.