CODE-077: blobHistory walks the ODB for what the REV-BLOB span answers in 40 ms

Now: OPEN
Sev: MED
Rep: ///bee
Ask: gritzko
Rev: ///bee#8cb69a0
See: BEE-070
See: BEE-033

Input

Context

index/perma.js:122:Ab,145,157 historyOf/blobHistory/blobsFor and index/hook.js:258:bn do a readCommit plus a tree descent per commit. On ~/src/linux kernel/sched/core.c: blobHistory 8240 ms vs 40 ms for the identical 1940-blob scope off dag.pathRevs' REV-BLOB span; mintRef calls it once per ref, unmemoised, INSIDE git commit. hashlet60 carries the 60 bits mintHashlet needs, so the index is a complete substitute. Found in the 2026-09-18 index review.

Goals

Serve blob history off the REV-BLOB span; memoize per (path, tip) within a mint run.

WIP

Design decisions

The scope is spelled in the index's own 15 hex (a hashlet60 IS an object name), not in full sha1s: the REV-BLOB val carries 60 bits and a 10-char hashlet reaches exactly those, so shaBits reads either spelling and nothing has to be named in full to be weighed. The clash test compares the same 15, so a 60-bit twin now mints an ambiguous hashlet where it used to mint none — no hashlet of any length tells such a pair apart anyway.
blobsFor rides the same span: it sieves the revs and only a MATCH costs a readCommit, so the follow drops from one tree descent per commit to one or two ODB reads.
The memo is keyed (root, tip, path) and capped at 256, swept whole like the CODE-034 caches, so a resident bee http cannot answer off a history that has moved.
Fallback: no REV-BLOB row for the path -> the old ODB walk. That walk takes its COMMIT list from the same REV-CMMT span (view/log.js fileLog), so a tip ahead of the mark truncates both legs alike; the index leg adds no staleness of its own.
Order: the span is rev order, the walk's topological one; the old walk sorted by committer date. On the test/perma fixture the two agree, which is what the repro pins; on linux's kernel/sched/core.c the SET is identical (1940, none missing, none extra) and 275 of the 1940 positions differ. No consumer reads the order — the scope is a membership test — and both mint the same hashlet, aY.

TODOs

[v] bench: mint of a ref into sched/core.c
[v] index-backed blobHistory

Blockers and bummers

None. historyOf stays as the ODB leg's commit list and is the fallback's only reader now.