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Clamp LibNum to Number to stop forkable stalling permanently - #81
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sduchesneau merged 1 commit intoOct 9, 2026
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A reader bug can announce a block's LIB num higher than its own num (sol-devnet incident: block 774 with LibNum 775). BlockInCurrentChain resolves LIB by walking parent links by number only, so a too-high LibNum makes it return a ref pairing an unrelated block ID with that num; MoveLIB stores it, and every later ReversibleSegment walk then bails out before ever reaching the stored ID, silently freezing the forkable's head forever while it keeps linking incoming blocks. Clamp the block's LibNum down to its own Number on entry and log an error, mirroring utils.ClampLibNum in firehose-core (streamingfast/firehose-core#284) for symmetry across both defenses.
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Oct 9, 2026
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I 100% agree with this fix
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Summary
BlockInCurrentChainresolves a LIB purely by walking parent links by number, so a too-high LIB num makes it return a ref pairing an unrelated block ID with that num.MoveLIBstores that mismatched ref, and every laterReversibleSegmentwalk then bails out as soon as it sees a real block num below that fake LIB num — without ever reaching the stored ID — silently freezing the forkable's head forever while it keeps linking incoming blocks (healthz stays green, nothing is ever emitted again).Forkable.ProcessBlocknow clamps a block'sLibNumdown to its ownNumberon entry (logs an error), instead of trying to special-case every LIB consumer downstream.block_num/block_id/original_lib_num) and test shape matchutils.ClampLibNumin firehose-core (Clamp invalid lib_num in the console reader path, always on firehose-core#284), the reader-side guard for the same invariant, for symmetry across both defenses.