forkchoice: simplify store's latest_justified and latest_finalized updates - #194
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Much better this way.
This was referenced Jun 13, 2026
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…ependent max on_block advanced latest_finalized by an independent monotonic max over every imported block's post-state, decoupled from latest_justified and the head. A fork that finalizes a higher slot but then loses head selection left its finalized checkpoint latched in the store, so latest_finalized could sit on a dead branch that is not an ancestor of the head. Validators then derive attestation targets against that phantom finalized while the canonical state transition validates against its own lower finalized, so every advancing target is rejected and finalization freezes. Keep the store's finalized only when it lies on the head's chain (a genuinely finalized checkpoint such as a checkpoint-sync anchor), advancing it to the head state's finalized; otherwise replace it with the head chain's finalized. This restores the consistency the forkchoice store had before leanEthereum#194 and matches the 3sf-mini reference, where the finalized checkpoint travels with the chosen state. Add a regression test: a dead fork finalizes slot 4 then loses to a heavier fork that justifies slot 7 but finalizes only slot 1; the store's finalized must track the head (slot 1), not the dead fork (slot 4).
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🗒️ Description
The fork choice store was relying on looping through the entire historical states to update itself to the latest_justified and latest_finalized checkpoints. This is an overkill and also problematic as the genesis state's latest_justified and latest_finalized block roots are set to 0x00... (the latter might also be an issue, I'll bring up as a separate PR)
Zeam is doing it more elegantly by simply just comparing the latest state's latest_justified and latest_finalized with the fork choice store, and update the store if the state contains higher checkpoints. So I propose bringing this optimization over.
This should not change the behavior of the fork choice so tests are unchanged.
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toxchecks to avoid unnecessary CI fails:uvx tox