feat(blockchain): pre-build proposer block one interval early#445
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MegaRedHand wants to merge 4 commits into
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feat(blockchain): pre-build proposer block one interval early#445MegaRedHand wants to merge 4 commits into
MegaRedHand wants to merge 4 commits into
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Proposers do heavy leanVM work (compact + merge_type_1s_into_type_2, ~2s) synchronously at interval 0 today. This starts that work at the previous slot's interval 4 on spawn_blocking workers (Phase A build, actor-side XMSS sign, Phase B merge), stores the result, and publishes it at interval 0 with a head/justified revalidation; on any mismatch or miss it falls back to the existing synchronous build, so there is no regression. Also fixes a finalization-breaking bug surfaced on devnet: the prebuild captured its head via get_proposal_head, which is not read-only (it ticks the store clock). Called one interval early it advanced the clock prematurely and stalled finalization. Capture the head read-only via store.head() instead.
…actor Replace the two-phase off-thread pre-build (spawn_blocking workers + PrebuildBuilt/PrebuildReady messages + session/cancel machinery) with a single synchronous build on the actor at the previous slot's interval 4. Removing the worker hop eliminates the timing race: the block is fully assembled before the interval-0 tick can consume it, so nearly every proposal is a hit instead of racing the merge against the 800ms window. Shared assemble_signed_block / process_and_publish_block helpers back both the synchronous proposal path and the pre-build. Blocking the actor during the build is acceptable: it has no other consensus-critical duty between interval 4 and the next slot. Devnet (4 nodes, 1 aggregator): finalization healthy (fin lag ~3), ~near-100% prebuild hit rate, zero skipped ticks, zero errors.
…n block_builder Remove the hit/miss/stale pre-build counters (block_building_time and the proposal phase histograms already cover the timing), and move PreparedBlock and prebuilt_block_is_usable from the standalone prebuild module into block_builder alongside PostBlockCheckpoints, which is where the rest of the block-building types live.
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What
Proposers do the heavy leanVM block-building work (attestation compaction + the Type-1 → Type-2 merge, ~1–2s) synchronously at interval 0 today, squeezed into the slot's first interval. This builds the next slot's block one interval early — at the previous slot's interval 4, synchronously on the blockchain actor — and publishes it at interval 0 after a revalidation. On any mismatch or failure it falls back to the existing synchronous build, so there is no regression.
How
prebuild_blockbuilds + signs + merges the full block against the current (read-only) head and stashes it as aPreparedBlock.propose_blockpublishes the prepared block iff it is still valid (prebuilt_block_is_usable: same slot/proposer, parent still the canonical head, and the built justified slot not behind the store's). Otherwise it rebuilds synchronously.assemble_signed_block/process_and_publish_blockhelpers back both the pre-build and the fallback path.sign_block_roottakes&mut self), so the build cannot be moved off-thread without risking OTS-index reuse.Finalization fix (included)
Capturing the pre-build head via
get_proposal_head— which is not read-only, it ticks the store clock — one interval early advanced the clock prematurely and stalled finalization. Fixed by capturing the head read-only viastore.head().Validation (local devnet: 4 ethlambda nodes, 1 aggregator)
Tradeoff
Building synchronously blocks the actor for the build duration at interval 4. This is acceptable: between interval 4 and the next slot the actor has no other consensus-critical duty, and the devnet run showed zero skipped ticks.
Tests
make fmt+cargo clippy -p ethlambda-blockchain --all-targets -- -D warningsclean; lib tests pass, including the newblock_builder::prebuild_testscovering the usability predicate.