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fix(alpenglow): fault picker whale overshoot & dead-slot hero tx loss - #2
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…ro tx loss Seed 9684: fault picker, not consensus. Pareto draw gave node 0 94.6% of stake. Picker took all 11 small nodes (5.4%), fell short, then "overshoot with one more node" grabbed the only one left: the whale. 100% offline, zero blocks, hero never submitted. Same code on main, so pre-existing. Fix: overshoot only when it lands closer to target than stopping short. New unit tests stake_pct_never_overshoots_with_a_whale, stake_pct_lands_near_target_for_pareto_stakes. Seed 19 (n=12): dead-slot inclusion. Leader kept producing slices for slots already Skip-certified. Hero landed in dead slot 2 after its Skip cert, so skip handler never fired, RPC saw block, stopped retrying. Fix: leader stops producing once Pool has Skip cert for slot; receivers ignore hero in skipped slot. Evidence - Sweep 164 seeds × 19.1% offline: 0 failures (was 5/104 before fixes). - cargo test --workspace green, 18 unit + 4 property tests. - Builtin scenario timings unchanged, wasm rebuilt, 4 Playwright specs pass.
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Summary
Two Alpenglow liveness bugs, both surfaced by the
alpenglow_20pct_offline_is_safe_and_liveproptest at ~19% offline:Target::StakePctovershoot heuristic grabbed the 94.6% whale when the 11 small nodes only summed to 5.4% → 100% offline, zero blocks, hero never submittedwith.abs_diff(goal) < acc.abs_diff(goal))produce_slicewhenpool.is_skipped(slot);on_block_completeno longer treats a block in a skipped slot as "landed"Changes
crates/sim-core/src/scenario.rs— overshoot guard refinement + 2 new unit tests (stake_pct_never_overshoots_with_a_whale,stake_pct_lands_near_target_for_pareto_stakes)crates/sim-core/src/protocol/alpenglow/mod.rs— dead-slot guard inproduce_slice+ skip check inon_block_completeCLAUDE.md— documents both fixes and the picker caveatweb/e2e/screenshots/compare-leader-down.png— regeneratedVerification
cargo test --workspace— 22/22 pass (18 unit + 4 property, incl.alpenglow_20pct_offline_is_safe_and_live)Caveat
The picker can now land below the target when stake is whale-dominated (19% → ~5% realized). Correct per the fix and documented in CLAUDE.md; the proptest liveness bound still holds since realized offline ≤ target.