How to know the code works without manually reviewing every agent-produced diff.

Pillar — Quality

How to know the code works without manually reviewing every agent-produced diff.

Status

◐ Scoped, not yet detailed.

Concern	Universal principle	Concrete pattern
Test pyramid	Unit > integration > E2E; cover the boundary contracts heavily	Vitest unit + Playwright E2E + contract-level params/result parse tests
Coverage target	>90% per shipped package, measured against statements	Per-package coverage threshold in CI; per-package, not whole-repo
Mutation testing	Beats coverage as a quality signal once unit suite is good	Stryker / mutation tool on stable utilities first
Hermetic tests	Component-level vitest preferred over live-app E2E	Reproduce + lock bugs via in-process tests, not Playwright
Verify-first close	Before reproducing an issue, check if it's already fixed	Default `gh issue view \<n\>` at session start
File-size gate	See architecture pillar	Baseline shrink-only
Lint gates	No `any`, no `console.log`, no default exports, no nested ternaries, no raw HTML	ESLint rule pack + per-file overrides
Quality-gates script	One `pnpm check:quality-gates` for fast structural checks	Parallel: lint + typecheck + secrets + size + intl + tokens
Sanity script	One `pnpm sanity` for cross-cutting rule audit	Generates `docs/audit/sanity-report.md`; CI fails on regressions
Pre-push hook	Runs structural gates + ADR/RFC checks; not full tests	Husky `pre-push`; tests on CI
Concurrency safety	Agents merge PRs against fast-moving main	Stash-verify red, rebase, retry; never `--theirs`/`--ours` blindly

Tests are part of the diff. No "tests next PR".
Coverage is per package, not aggregate. Aggregate hides which package is bad.
Hermetic over E2E for bug repro. Component tests fail in 2s; Playwright fails in 60s and lies more.
Gates produce actionable messages. "Lint failed" is not actionable. "src/x.ts:42 — no any in boundary file; use unknown and parse." is.
Pre-push is the safety net, not the proof. Run check:all before a release.

Doc	Read when
`universal.md`	First read; the 9 non-negotiables
`test-pyramid.md`	Test-tier distribution + escalation
`quality-gates-pattern.md`	Structural gate suite + orchestrator
`pre-push-pattern.md`	Three-tier hook split
`sanity-pattern.md`	Cross-cutting audit
`mutation-testing-pattern.md`	Beyond coverage
`observability-pattern.md`	Metrics / logs / traces / SLOs
`performance-budgets-pattern.md`	Bundle / latency / resource budgets
`chaos-engineering-pattern.md`	Controlled fault injection
`ci-cd-pipeline-pattern.md`	Commit → prod pipeline; caching; deploy patterns; DB migrations
`alerting-runbooks-pattern.md`	SLO burn-rate alerts; runbook 5-section template; tuning loop
`cost-optimization-pattern.md`	FinOps; per-tenant attribution; right-sizing; commitments + spot
`contract-testing-pattern.md`	Pact + schema-first; consumer-driven contracts; broker; can-i-deploy
`product-analytics-experimentation-pattern.md`	Event tracking; funnels + cohorts; A/B experiments; holdouts