CODE-064: path_hl collisions: undetected in the rev lane, per-worktree in kv

Now: OPEN
Sev: LOW
Rep: ///bee
Ask: gritzko
Rev: ///bee#8cb69a0
See: BEE-024
See: LITE-006

Input

Context

index/index.js:128:Wt pathHl is 40 bits and the rev lane never detects a collision: two files on one hashlet share one rev chain and their histories merge (about 0.5% likely per 100k-path repo, and INDEXES.mkd "What is NOT indexed" does not declare it). index/kv.js:314:9B-334 builds its detector from THIS worktree's files only while the lane is shared across linked worktrees (BEE-009), so a cross-worktree collision goes undetected and each sweep reconciles into the other's block, flipping the header wt; INDEXES.mkd's "the sweep holds the COMPLETE path list" is a doc/code discrepancy there. Found in the 2026-09-18 index review.

Goals

State the rev-lane limit in INDEXES.mkd (or detect it off the FSEG row's segment hashes); fold other worktrees' live blocks into the kv detector.

WIP

Design decisions

The kv detector now weighs the LIVE blocks of the other checkouts beside its own path list: a file whose hashlet another living worktree already owns is read DIRECTLY and puts nothing, so the header wt never flips. The first worktree to index a hashlet keeps it; a block whose owner is gone is collected by CODE-063 and the hashlet frees up.
The rev lane is DOCUMENTED, not fixed. FSEG keys the filename (6|fn_hl:40|prnt_hl:20), so its segment hashes cannot be reached from a path_hl; a check off them needs the path_hl stored beside them, i.e. a format change. gritzko decides whether that lane is worth widening.

TODOs

[v] doc: rev-lane collision declared
[v] kv detector sees every worktree's blocks

Blockers and bummers

Rev-lane detection needs a new or widened record, so it is left as the INDEXES.mkd "What is NOT indexed" entry.