---
id: 02-pre-commit-check-script
epic: 2026-05-14-library-evaluation-policy
title: Pre-commit check script for library trace presence
type: technical-story
status: done
feature: scripts
depends-on: [01-trace-schema-foundation]
blocks: [06-sandcastle-reviewer-prompt]
---

## Goal

Write `scripts/library-decisions/check.mjs` — the script that walks staged `package.json` diffs, derives the tier of each affected package, and fails the commit when a new runtime dependency in a feature- or core-tier package has no sibling approved trace staged. Wire it into `.husky/pre-commit` as step 4.

## Why

Human and agent reviewers cannot reliably check trace presence during code review. The pre-commit hook is the last mechanical gate before a dep reaches the repo; it runs unconditionally, composes with `--no-verify` protection already in the bash-guard hook, and gives the committer immediate actionable feedback.

## Done when

- `scripts/library-decisions/check.mjs` exists and: (1) reads `git diff --cached --name-only -- '**/package.json'`; (2) for each staged `package.json`, derives tier from path (`apps/*` → app, `packages/core-*` → core, `packages/*` → feature); (3) for each newly added line in `dependencies` (not `devDependencies` / `peerDependencies`), checks that `docs/library-decisions/*-<name>.md` is also staged with `decision: approved`; (4) exits 1 with a per-package error report + pointer to the skill when any check fails; (5) app-tier and devdep additions exit 0 silently.
- `.husky/pre-commit` invokes `node scripts/library-decisions/check.mjs` after the existing state-sync guard.
- `scripts/library-decisions/check.test.mjs` covers (using a temp git repo fixture): new feature-tier dep without trace → exit 1; new feature-tier dep with approved trace staged → exit 0; new feature-tier dep with rejected-decision trace staged → exit 1; new app-tier dep → exit 0; new devdep → exit 0; multi-file diff with mixed pass/fail → exit 1 with per-package report; `peerDependencies`-only change → exit 0.
- `pnpm typecheck && pnpm lint && pnpm test && pnpm conformance && pnpm fallow:audit && pnpm coverage:diff` all pass.

## In scope

- `scripts/library-decisions/check.mjs` — the check script (imports `schema.mjs` from Story 01 for trace validation).
- `scripts/library-decisions/check.test.mjs` — integration tests using a temp git repo fixture (mirror pattern from `scripts/work/state-sync-guard.mjs` tests).
- `.husky/pre-commit` — one added line.

## Out of scope

- Sandcastle reviewer prompt integration — Story 06.
- `--staged-against <base>` flag for CI/sandcastle use — added in Story 06 when the reviewer prompt is written.
- `pnpm libs check` ergonomic wrapper — deferred per PRD.

## Tasks

- [x] Write `scripts/library-decisions/check.mjs` (imports schema from Story 01; parses `git diff --cached` output; tier derivation from path; staged-trace presence + `decision: approved` check; exit-1 report with skill pointer); wire into `.husky/pre-commit`; write `check.test.mjs` integration tests with temp git repo fixture covering all 7 cases from Done when; all gates pass on this single commit.
