Adds the day-to-day cookbook for the 4-layer coverage architecture
(ADR-020) and threads it into the discovery path:
docs/guides/coverage.md (new):
- 4 layers at a glance + when each fires
- Single-source-of-truth pattern (feature.manifest.ts coverage:
section) and the three readers (vitest, assertFeatureConformance,
coverage:diff)
- Daily workflow: pnpm test --coverage -> aggregate -> diff
- How to read a failure (stderr human + stdout JSON examples)
- How to fix uncovered slices (TDD walkthrough)
- The full allowlist (test files, configs, docs, scripts, dev
tooling, per-feature excludes)
- Adjusting bands (manifest-first, when to override vitest)
- CI behavior (two workflows: validate + coverage-snapshot)
- Reading the committed trend via git log -- coverage/summary.json
- Mutation testing primer (L3, opt-in, scope, lands in next story)
- Troubleshooting
CLAUDE.md Read First gets the new guide pinned between audit and
template-tiers, with the L0-L3 layer summary inline so agents see the
shape at a glance.
Feature generator updates (turbo/generators/templates/feature/):
- feature.manifest.ts.hbs: new `coverage:` block at <gen:coverage>
anchor scaffolded with the documented defaults + mutationTargets
- vitest.config.ts.hbs: now uses vitestThresholdsFromBands(
DEFAULT_COVERAGE_BANDS) instead of the duplicated literal — new
features ship conformance-compliant by default
Next features generated via `pnpm turbo gen feature` are coverage-
aware from the first commit: bands declared in manifest, vitest
config consumes the helper, no duplication to drift.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Danijel Martinek
f4254aae48