Follow-up to the bug fixed in:
- https://github.com/sigp/lighthouse/pull/8121
This fixes the root cause of that bug, which was introduced by me in:
- https://github.com/sigp/lighthouse/pull/8101
Lion identified the issue here:
- https://github.com/sigp/lighthouse/pull/8101#discussion_r2382710356
In the methods that compute the proposer shuffling decision root, ensure we don't use lookahead for the Fulu fork epoch itself. This is accomplished by checking if Fulu is enabled at `epoch - 1`, i.e. if `epoch > fulu_fork_epoch`.
I haven't updated the methods that _compute_ shufflings to use these new corrected bounds (e.g. `BeaconState::compute_proposer_indices`), although we could make this change in future. The `get_beacon_proposer_indices` method already gracefully handles the Fulu boundary case by using the `proposer_lookahead` field (if initialised).
Co-Authored-By: Michael Sproul <michael@sigmaprime.io>
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