Claimed a rebuilt binary would resume on the current data, reasoning from upstream's "not a format change" rather than from this codebase. That claim decides whether adopting the fix costs a rebuild or costs 1.37 TB, so it needed checking. segment_footer.zig writes an 8-byte region header carrying block count and per-bloom size ahead of the per-block blooms, and segment.zig blockBloomBlobs reads both back and indexes by multiplication. Nothing assumes 8,409 or the 4096 capacity anywhere in the read path. A segment sealed with fixed-size blooms records size=8409 and still reads; a right-sized one records its own size and reads identically, so both coexist in one archive. That is the equal-size-region invariant upstream describes, already implemented here. A rebuilt binary resumes on the current 3.8M repositories. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>