Add GitHub Actions test workflow running on every PR against Node 18 and 20

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Description

Create .github/workflows/test.yml that runs npm test on Node 18 and Node 20 for every pull_request and push to main. Must use the mock layer exclusively — no GitHub token required. Report test results as a PR check.

Acceptance Criteria

• Add GitHub Actions test workflow running on every PR against Node 18 and 20

Milestone Context

Milestone	v6 — Local Testing & Simulation Framework
Phase	Phase 50: CI Integration & Coverage
GSD Route	quick
Phase Position	Phase 4 of 4 in milestone

Milestone Goal

Offline test suite with mock GitHub API and fake GSD agents to validate MGW orchestration logic without requiring live GitHub tokens or active Claude API calls.

Phase Goal

Wire the test suite into CI, enforce coverage thresholds, and add a local test helper so contributors can run the full suite in one step.

Dependencies

write-scenario-tests-for-mgwsync-drift-detection

Scope Hints

• Estimated route: quick
• Labels: testing,ci

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MGW · work-started · 2026-03-06T10:50:22Z
Milestone: v6 — Local Testing & Simulation Framework | Phase 50: CI Integration & Coverage

Work Started

Issue	#256 — Add GitHub Actions test workflow running on every PR against Node 18 and 20
Route	plan-phase
Phase	50 — CI Integration & Coverage
Position	10 of 11

Pipeline executing autonomously...

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MGW · pr-ready · 2026-03-06T10:55:30Z
Milestone: v6 — Local Testing & Simulation Framework | Phase 50: CI Integration & Coverage

PR Ready

PR #267 — #267

Added .github/workflows/test.yml — dedicated CI workflow running npm test on Node 18 and 20 for every PR and push to main. No GitHub token required.

Testing procedures posted on the PR.
This issue will auto-close when the PR is merged.

Pipeline Summary

Stage	Status
Triage	✓
Planning	✓
Execution	✓
PR Creation	✓

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MGW · pr-ready · 2026-03-06T11:00:45Z
Milestone: v6 — Local Testing & Simulation Framework | Phase 50: CI Integration & Coverage

PR Ready

PR #267 — #267

Milestone Progress (10/11 complete)

#	Issue	Status	PR
247	Create lib/mock-github.cjs	✓ Done	#258
248	Create lib/mock-gsd-agent.cjs	✓ Done	#259
249	Add vitest test runner	✓ Done	#260
250	Integration tests: validate_and_load	✓ Done	#261
251	Tests: checkpoint read/write	✓ Done	#262
252	Pipeline stage transition tests	✓ Done	#263
253	Scenario tests: mgw:project	✓ Done	#264
254	Scenario tests: mgw:milestone	✓ Done	#265
255	Scenario tests: mgw:sync	✓ Done	#266
256	GitHub Actions test workflow	✓ Done	#267
257	Vitest coverage reporting	○ Pending	—