084 — Quality Metrics {Testing}

Purpose

Define, collect, and enforce quantitative quality thresholds across the entire stack. Every metric has a target, a measurement tool, and a CI enforcement gate. [EXPLICIT]

Physics — 3 Immutable Laws

1. Law of Measurement: What is not measured degrades. Every quality dimension has a numeric target tracked over time. [EXPLICIT]
2. Law of Thresholds: Metrics without enforced thresholds are vanity metrics. Every metric has a pass/fail gate in CI. [EXPLICIT]
3. Law of Trends: Absolute values matter less than direction. A metric moving in the wrong direction for 3 consecutive sprints triggers intervention. [EXPLICIT]

Protocol

Phase 1 — Metric Collection

1. Code coverage: vitest --coverage or jest --coverage → lcov report. [EXPLICIT]
2. Cyclomatic complexity: eslint-plugin-complexity with max 15 per function. [EXPLICIT]
3. Duplication: jscpd with threshold < 5% duplication. [EXPLICIT]
4. Lighthouse: lighthouse-ci for Performance, Accessibility, Best Practices, SEO. [EXPLICIT]
5. Bundle size: size-limit or bundlesize with per-route budgets. [EXPLICIT]
6. Firestore I/O: Cloud Monitoring dashboard tracking read/write/delete counts per day. [EXPLICIT]

Phase 2 — Dashboard & Reporting

1. Aggregate metrics in CI summary (GitHub Actions job summary). [EXPLICIT]
2. Track trends in spreadsheet or dashboard (weekly snapshot). [EXPLICIT]
3. Flag regressions as PR comments via danger.js or custom action. [EXPLICIT]

I/O

Input	Output
Source code	Coverage report (lcov, HTML)
ESLint config	Complexity report per function
Built bundle	Bundle size report (per-chunk)
Deployed URL	Lighthouse JSON + HTML report
Firebase project	Firestore read/write daily counts

Quality Gates — 5 Checks

1. Coverage >= 80% lines, branches, functions, statements. [EXPLICIT]
2. Cyclomatic complexity <= 15 per function — no exceptions. [EXPLICIT]
3. Code duplication < 5% across codebase. [EXPLICIT]
4. Lighthouse scores: Performance >= 90, Accessibility >= 95, Best Practices >= 90, SEO >= 90. [EXPLICIT]
5. Bundle size < 250KB initial load (gzipped) — per-route budgets enforced. [EXPLICIT]

Edge Cases

• Monorepo projects: Measure metrics per package, not aggregate only.
• Third-party code: Exclude node_modules and generated files from duplication/complexity.
• Lighthouse variance: Run 3x and take median to reduce noise.
• Firestore spikes: Set billing alert at 50K reads/day. Investigate any 3x spike.

Self-Correction Triggers

• Any metric below threshold for 2 consecutive PRs → block merge until fixed.
• Lighthouse performance drops below 80 → performance audit sprint (skill 096).
• Bundle size exceeds budget → run bundle analysis (skill 099).
• Firestore reads spike 3x → review queries, add caching (skill 100).

Usage

Example invocations:

• "/quality-metrics" — Run the full quality metrics workflow
• "quality metrics on this project" — Apply to current context

Assumptions & Limits

• Assumes access to project artifacts (code, docs, configs) [EXPLICIT]
• Requires English-language output unless otherwise specified [EXPLICIT]
• Does not replace domain expert judgment for final decisions [EXPLICIT]