sketch for auto suspension

[drsk0]

Purpose

Discuss how to trigger suspension at snapshot. I filled in most of the missing pieces, but would like to be sure, that processSuspensions is doing the right thing.

Changes

_Describe the changes that were needed.

Checklist

• My code follows the style of this project.
• The code compiles without warnings.
• I have performed a self-review of the changes.
• I have documented my code, in particular the intent of the
  hard-to-understand areas.
• (If necessary) I have updated the CHANGELOG.

CLA acceptance

_Remove if not applicable.

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Contributor License Agreement v1.0

• link: https://developers.concordium.com/CLAs/Contributor-License-Agreement-v1.0.pdf

• I accept the above linked CLA.

[td202]

Could combine the boolean flags with a bitmap.

[td202]

This is looking good. I think it would be helpful to refine what the missed block count and primed for suspension actually mean.

• Missed block count: rounds that a validator won but failed to bake a block since the last round that a validator contributed to as a baker or finalizer, since it most recently became a (non-suspended) member of the validator committee.
• Primed for suspension: should be set on a payday when the missed block count exceeds the threshold. Should be cleared when the validator contributes again. At the snapshot epoch, validators that are primed will not be included in the next committee and will be set as suspended (if still an active validator).

If the payday length is 1 epoch, then each payday transition is also the snapshot for the next payday. For this to make sense, we need to determine the set of validators that should get suspended (i.e. the ones that are already marked as primed) before marking any validators as primed. I think this is consistent with the order of operations discussed elsewhere in this review.

[td202]

Suggested change

	(theState9, isSnapshot) <-
	if newEpoch + 1 == newNextPayday
	let isSnapshot = newEpoch + 1 == newNextPayday
	theState9 <-
	if isSnapshot

[td202]

Here, we're calculating the the validators for the next payday, so we should take into account which validators are going to be suspended here and exclude them. (Not just the ones that are already suspended.) I would suggest we should calculate the validators that are going to be suspended (i.e. check which ones are primed) here, exclude them from the calculation in computeBakerStakesAndCapital, and then return this set which is then passed on to processSuspensions to actually suspend them in the epilogue.

[drsk0]

This has been fully implemented now. I'll open two separate PR to bring the changes in. First one is #1264. This are only the new data structures. The second one will contain the implementation.