BE-017 HIGH: io.mmap-and-never-unmap leak class regresses across 4 sites (JS-031 redux)

Four read paths io.mmap a file and never unmap it — the exact leak class JS-031 purged from classify, reappearing in the resident loop where mappings accumulate until the process exits (region exhaustion on a big-tree diff or repeated blame):

shared/util/ignore.js:155 — readFileText mmaps every .gitignore on the walk, never unmaps.
views/diff/diff.js:313 — whole-tree diff mmaps EVERY wt file, never unmaps.
shared/gitmodules.js:16 — .gitmodules read mmaps per call, never unmaps (also hand-concats the path instead of pathlib.join).
views/why/why.js:25 — readWtFile mmaps per blame, leaks one mapping each in the resident loop.

From the 2026-07-07 be/ review (BE/REVIEW), all CONFIRMED. Method Issues.

Input

Context

jab has no deterministic unmap primitive today (JAB buf.cpp:124 — io.book/close/trim documented but unimplemented); the leak is that the mapping is held for the run with no release point even where one should exist. Reads that only need bytes should route through shared/wtread.js (the ONE reg-file read) which owns the lifecycle.
JS-031 already established the fix pattern in classify — these sites missed the sweep or landed after.

Goals

Each site reads via a lifecycle-owning helper (wtread) or explicitly releases its mapping; no mapping outlives the read in the resident loop.
gitmodules path built with pathlib.join.

Constraints

Repro-first where measurable: a resident-loop blame/diff loop asserting bounded mappings (or a mapping-count probe). May depend on a jab unmap primitive — coordinate with JAB (buf.cpp:124); if none, size/scope the reads to bound the leak.

WIP

Design decisions

(pending — route through wtread vs explicit unmap; gated on the jab unmap primitive)

TODOs

Route the 4 sites through a lifecycle-owning read; gitmodules pathlib.join.
Bounded-mapping check; suite green.

Blockers and bummers

Deterministic unmap may not exist in jab yet (JAB buf.cpp:124) — the real fix may need that primitive first.

Outcome

(pending)