scripts/pm/git-history.mjs is the prescribed shallow-history remedy and is named in no instruction file, so a seat asking a churn question has no way to find it #10508

Found while implementing #9902 (PR #10506). Filing rather than widening that PR: the remedy is a governed edit, and governed surfaces are human-merge-only and never a rider on a code PR.

The gap

scripts/pm/git-history.mjs shipped for #9878 as the answer to "how many commits landed in this window" — it proves the window is covered, deepens only when the shallow floor intrudes, and otherwise refuses with an empty stdout so a captured number is empty rather than plausible.

Before PR #10506, grep -rn git-history across the whole repo returned only the file itself: no package.json script, no workflow step, no skill, no AGENTS.md entry. Two consequences, one of which is now closed:

• Its self-test never ran anywhere. Closed by PR fix(pm-tooling): refuse windowed history questions a shallow clone cannot see all of #10506, which runs it in lint.yml.
• Nothing points a seat at it. Still open, and this is the half that produced Three seat-run tools ask windowed history questions with no shallow guard, so each answers plausibly and wrongly in an agent container #9902 in the first place: three tools asked windowed history questions with no guard while the guard sat one directory away. An agent that does not know a tool exists re-derives the wrong answer by hand — which is exactly the failure the tool prevents, and it is silent.

The remedy, which needs a human merge

The two natural homes are both governed surfaces (docs/adr/** + .claude/** + skills/** + AGENTS.md + CLAUDE.md, maintainer 2026-08-18):

• AGENTS.md guard index — one line, in the same shape as the other entries.
• .claude/skills/pm-dispatch/SKILL.md tool table — it already lists scripts/pm/check-governed-merges.mjs, and the PM seat is the heaviest asker of windowed history questions (round reports quote churn counts).

Per check-governed-merges.mjs's own register this is domain:skills territory (SKILL.md: 「skills 相关的应该都归你管」, maintainer 2026-08-18), not domain:devx.

Suggested wording, so the routing seat has something to accept or reject rather than compose:

scripts/pm/git-history.mjs — answer a "how many commits on <ref> in <window>" question, or REFUSE. A shallow clone answers windowed git log/rev-list questions from truncated history at exit 0 with no warning; this proves the window is covered first. historyHorizon() is the read-only predicate for tools that answer their own question.

Related

#9878 (the helper) · #9902 (the three call sites) · PR #10506

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