agentic-dev/docs/work/2026-05-14-library-evaluation-policy/06-sandcastle-reviewer-prompt/_story.md

id, epic, title, type, status, feature, depends-on, blocks

id	epic	title	type	status	feature	depends-on	blocks
06-sandcastle-reviewer-prompt	2026-05-14-library-evaluation-policy	Sandcastle reviewer prompt — Library-trace check section	technical-story	done	tooling	02-pre-commit-check-script

Goal

Append a "Library-trace check" section to .sandcastle/reviewer.prompt.md instructing the reviewer agent to run node scripts/library-decisions/check.mjs --staged-against <base> before issuing its verdict, and add the --staged-against <base> flag to check.mjs so it can compare against a given base ref rather than only the git index.

Why

The sandcastle reviewer runs in a clean sandbox where git diff --cached may not reflect the full branch diff. The --staged-against <base> flag allows the reviewer to pass the PR's base branch as the comparison point, giving the same check a CI-compatible code path. Without this, the fourth enforcement layer is advisory only — it has no mechanical check to back it up.

Done when

• scripts/library-decisions/check.mjs accepts a --staged-against <base> flag; when present, compares git diff <base>...HEAD -- '**/package.json' instead of git diff --cached.
• check.test.mjs has a new test case: --staged-against main mode with a new feature-tier dep and no trace → exit 1.
• .sandcastle/reviewer.prompt.md contains a "Library-trace check" section (appended, not replacing existing content) instructing the reviewer to run node scripts/library-decisions/check.mjs --staged-against <base-branch> and reject the slice if it exits non-zero.
• pnpm lint && pnpm test && pnpm fallow:audit && pnpm coverage:diff all pass.

In scope

• scripts/library-decisions/check.mjs — add --staged-against flag.
• scripts/library-decisions/check.test.mjs — add test for the new flag.
• .sandcastle/reviewer.prompt.md — append the Library-trace check section.

Out of scope

• Changing the reviewer prompt's existing sections.
• The pre-commit (index-mode) check behavior — already in Story 02.
• CI integration (GitHub Actions) — deferred.

Tasks

• Add --staged-against <base> flag to check.mjs (switches from git diff --cached to git diff <base>...HEAD); add a test covering --staged-against mode (temp git repo fixture, new feature-tier dep, no trace → exit 1); append "Library-trace check" section to .sandcastle/reviewer.prompt.md with the node scripts/library-decisions/check.mjs --staged-against <base> invocation and reject instruction; all gates pass on this single commit.