SIMD-0080: Allow commission decrease at any time during an epoch

proposals/0080-allow_commission_decrease_at_any_time.md

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+---
+simd: '0080'
+title: Allow Commission Decrease at Any Time
+authors:
+  - Bryan Ischo ([email protected])
+category: Standard
+type: Core
+status: Draft
+created: 2023-10-26
+feature: TBD
+---
+
+## Summary
+
+The commission_updates_only_allowed_in_first_half_of_epoch feature disallows
+commission decrease in the second half of epoch. Given that the purpose of this
+feature was to prevent 'rug pulls' which are accomplished by increasing
+commission at the end of epoch and then decreasing commission at the beginning
+of next epoch, disallowing decreases during the second half of epoch is
+unnecessary.
+
+A feature gate must be added to support this SIMD as all validators' vote
+programs must treat commission change instructions the same or else consensus
+will diverge.
+
+## Motivation
+
+Some validator operators may need to decrease commission in order to satisfy
+their own operational criteria.  Speaking personally, when I have an operator
+error that results in reduced stake account rewards for the epoch, I reduce
+commission to 0% to ensure that stake accounts are not disadvantaged by my
+actions. Not being allowed to do this in the second half of an epoch is a real
+problem for me.
+
+Allowing commission changes during the second half of epochs also enables
+"reverse rug pulls" where a validator has commission set to 100% during the
+majority of an epoch but reduces it to 0% across the epoch boundary.  It's not
+clear why some validator operators choose to do this, but it does not seem
+harmful, and there does appear to be motivation for some validators to do this
+as it's been done numerous times in the past.
+
+## Alternatives Considered
+
+No alternatives were considered.
+
+## New Terminology
+
+Reverse Rug Pull: Setting commission to 100% for most of an epoch, and to 0%
+only across epoch boundaries.  This has the effect of discouraging third party
+stake to a validator while still charging 0% commission.  This is not considered
+to be a technique harmful to stakers.
+
+## Detailed Design
+
+A feature will be added which will enable set-commission logic to first check
+whether the proposed commission change is a decrease, and if so, do not invoke
+the "only allow commission change in first half of epoch" rule.
+
+In order to facilitate testing, all of the functionality for handling the
+set-commission vote program instruction will be moved into the vote state module
+instead of being half in the vote instruction processing logic and half in the
+vote state module.  All of the functionality being in the vote state module will
+allow a new test which tests just commission updates at various points within an
+epoch to be written.
+
+## Impact
+
+Validators will now be able to decrease commission at any time in the epoch, but
+only increase commission in the first half of epochs (because of the
+commission_updates_only_allowed_in_first_half_of_epoch feature already
+implemented).
+
+## Security Considerations
+
+None
+
+## Drawbacks
+
+It may cause additional confusion to validators who might not understand why
+some types of commission changes succeed only in the first half of epochs while
+others succeed always.
+
+## Backwards Compatibility
+
+This feature requires a feature gate because software which includes the
+implementation will allow certain set-commission transactions to succeed where
+software without the implementation would fail those transactions.  Thus all
+validators must be updated to the new functionality at an epoch boundary so that
+all validators agree on the result of executing those transactions.