ci(#17): code coverage measurement + ratchet gate (baseline 57.31%)

[Cadacious]

Implements #17 — code coverage measurement + a hardened ratchet gate in build.ps1.

Baseline

57.31% overall (1199 tests), measured from the real suite via Pester JaCoCo — up from 33.2%. coverage-baseline.json holds overall + a 16-module per-module map.

How it works (Gate 3, opt-in -Coverage / -CodeCoverage)

• Overall ratchet: fails if measured overall drops more than a 0.30pt tolerance below baseline (~15x the measured ~0.02pt jitter).
• Per-module floors (enforced, not decorative): every module in the baseline is checked on every run; a module dropping >0.30pt below its own baseline fails and is named — even if overall stays within tolerance (so one module's gain can't mask another's collapse).
• Anti-tamper absolute floor (50%): a measured overall or a committed baseline.overall below 50% fails as gutted/tampered, so the baseline can't be edited down to defeat the gate.
• Desync guards: a new module absent from the baseline is WARNed (with the value to add); a baseline module that vanished fails with guidance.
• On a >1pt rise, prints a ratchet: baseline can be raised hint (never auto-raises). Reuses the single Invoke-Pester run (+~14s for instrumentation). CI uploads coverage.xml; CONTRIBUTING documents the per-module raise process.

Proof

Per-module gate: raised VSSManager's baseline → build failed naming it while overall passed. Absolute floor: baseline.overall=5 → failed "implausible/tampered". Plain ./build.ps1 stays BUILD OK with the gate skipped.

Closes #17.

🤖 Generated with Claude Code

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ℹ️ Review info

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📥 Commits

Reviewing files that changed from the base of the PR and between 73ebdb8 and 67eb241.

📒 Files selected for processing (5)

• .github/CONTRIBUTING.md
• .github/workflows/ci.yml
• .gitignore
• build.ps1
• coverage-baseline.json

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch ci/17-coverage-gate

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[Copilot]

Pull request overview

Adds opt-in code coverage measurement and a “ratchet” gate to the PowerShell build entrypoint so CI enforces that overall coverage does not regress beyond a small tolerance, while also publishing the JaCoCo coverage report as a CI artifact.

Changes:

• Introduces a committed coverage-baseline.json (overall + per-module baseline map) used by the coverage ratchet gate.
• Extends build.ps1 with a -Coverage switch to enable Pester JaCoCo collection and enforce the baseline/tolerance gate.
• Updates CI to run coverage mode and upload coverage.xml, and documents the workflow in CONTRIBUTING.

Reviewed changes

Copilot reviewed 4 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
coverage-baseline.json	Adds the committed baseline (overall + per-module) used by the coverage ratchet gate.
build.ps1	Adds opt-in Pester JaCoCo coverage collection and a baseline/tolerance “ratchet” failure gate.
.gitignore	Ensures coverage outputs stay ignored while explicitly tracking coverage-baseline.json.
.github/workflows/ci.yml	Runs build.ps1 with coverage enabled and uploads coverage.xml as an artifact.
.github/CONTRIBUTING.md	Documents how the coverage gate works and how to raise the baseline deliberately.

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Pull request overview

Copilot reviewed 4 out of 5 changed files in this pull request and generated 1 comment.