Power: Process batch proof verifications before deferred cron events

[wadealexc]

From OnEpochTickEnd:

specs-actors/actors/builtin/power/power_actor.go

Lines 200 to 201 in 0f9f59a

	a.processDeferredCronEvents(rt)
	a.processBatchProofVerifies(rt)

This would also involve some changes to the Miner actor. For example, precommit expiry bound could remove the additional "+1":

specs-actors/actors/builtin/miner/miner_actor.go

Lines 516 to 520 in 0f9f59a

	// The +1 here is critical for the batch verification of proofs. Without it, if a proof arrived exactly on the
	// due epoch, ProveCommitSector would accept it, then the expiry event would remove it, and then
	// ConfirmSectorProofsValid would fail to find it.
	expiryBound := rt.CurrEpoch() + msd + 1
	enrollCronEvent(rt, expiryBound, &cronPayload)

[wadealexc]

ConfirmSectorProofsValid reschedules expirations for replaced sectors to the end of their next deadline window:

specs-actors/actors/builtin/miner/miner_actor.go

Lines 662 to 665 in 8735710

	// Schedule expiration for replaced sectors to the end of their next deadline window.
	// They can't be removed right now because we want to challenge them immediately before termination.
	err = st.RescheduleSectorExpirations(store, rt.CurrEpoch(), info.SectorSize, replaceSectors)
	builtin.RequireNoErr(rt, err, exitcode.ErrIllegalState, "failed to replace sector expirations")

If the sector to be replaced is in a deadline whose Close epoch is CurrEpoch + 1, the new expiration chosen is equal to CurrEpoch:

specs-actors/actors/builtin/miner/miner_state.go

Lines 442 to 444 in 8735710

	if err = deadlineSectors.ForEach(func(dlIdx uint64, pm PartitionSectorMap) error {
	dlInfo := NewDeadlineInfo(st.ProvingPeriodStart, dlIdx, currEpoch).NextNotElapsed()
	newExpiration := dlInfo.Last()

Because the power actor processes batch proof verification after deferred cron events, the handleProvingPeriod cron event won't catch this expiry immediately:

specs-actors/actors/builtin/miner/miner_actor.go

Lines 1579 to 1581 in 8735710

	// Expire sectors that are due, either for on-time expiration or "early" faulty-for-too-long.
	expired, err := deadline.PopExpiredSectors(store, dlInfo.Last(), quant)
	builtin.RequireNoErr(rt, err, exitcode.ErrIllegalState, "failed to load expired sectors")

If I understand correctly, this means that the miner won't lose power for the replaced sector until the next day.

[anorth]

FYI @acruikshank an example of something for which we need a scenario test.