Revert the extract-first seal; restore merge-then-extract#796
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frankmcsherry merged 1 commit intoJul 13, 2026
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The extract-first seal (TimelyDataflow#793) folded the returned frontier during the per-chain extract, before cross-chain consolidation, so a kept time whose updates cancel across two un-merged chains was wrongly reported — the batcher held a capability that never discharges, stalling progress. Restore the merge-then-extract seal: all chains merge into one (consolidating equal (data,time), dropping zeros) before extract folds the frontier, so the frontier reflects post-consolidation distinct times. Keeps regression tests (frontier_is_post_consolidation) so the property is guarded if a future seal revisits the extract-first idea. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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Rewrite the release-plz-generated changelogs into the house style: categorized Added/Changed/Removed sections plus a closing summary of the breaking surface. Add the omitted timely 0.31 bump, drop the reverted extract-first seal pair (#793/#796), de-duplicate the HRTB entries, and flag the new Chunk and JoinTactic/ReduceTactic surface as experimental. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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The extract-first seal (#793) folded the returned frontier during the per-chain
extract, before cross-chain consolidation. Two ladder chains that never merged
can carry cancelling updates at the same kept time (an insert and a retract of
one record at a future/delayed time, arriving in different batches); their diffs
net to zero, so that time needs no capability — but per-chain extract inserts it
into the frontier from each chain, and the batcher then holds a capability it
can never discharge (the chains may sit un-merged indefinitely under the
geometric ladder), stalling progress. It affects every MergeBatcher, including
the mainline VecMerger-backed OrdVal/OrdKey batchers.
This restores merge-then-extract: all chains merge into one (consolidating equal
(data, time), dropping zeros) before extract folds the frontier, so the frontier
reflects the post-consolidation set of distinct kept times. Cost is ~14% on the
SCC benchmark — exactly the seal-side win #793 had claimed.
Adds merge_batcher unit tests (frontier_is_post_consolidation) guarding the
property, so a future seal that revisits the extract-first idea can't silently
reintroduce the bug.