Mutation testing (nightly) #2

	name: Mutation testing (nightly)

	# Stryker mutation testing on traces.js. Runs nightly because a full
	# pass is ~2-15 minutes depending on cache state; that's too slow for
	# per-PR gating. Per-PR confidence comes from `npm run test:coverage`
	# (c8 gate) — mutation testing complements coverage with kill ratio.
	#
	# Workflow:
	# - Scheduled at 03:00 UTC (off-peak)
	# - Manual trigger via Actions → "Mutation testing (nightly)" → Run
	# - Artifacts uploaded on every run (success or failure) so the
	# HTML report and incremental cache are inspectable post-run.
	#
	# Tightening cadence: see docs/qa-strategy.md § Mutation Testing.

	on:
	schedule:
	- cron: '0 3 * * *' # 03:00 UTC nightly
	workflow_dispatch: {}

	env:
	FORCE_JAVASCRIPT_ACTIONS_TO_NODE24: 'true'

	jobs:
	mutation:
	runs-on: ubuntu-latest
	timeout-minutes: 45
	steps:
	- uses: actions/checkout@v4
	with:
	fetch-depth: 0 # incremental run needs git history
	- uses: actions/setup-node@v4
	with:
	node-version: '20'
	cache: 'npm'
	- run: npm ci
	- name: Run Stryker
	run: npm run mutation
	- name: Save Stryker incremental cache
	if: always()
	uses: actions/cache/save@v4
	with:
	path: reports/stryker-incremental.json
	key: stryker-incremental-main
	- name: Upload mutation report
	if: always()
	uses: actions/upload-artifact@v4
	with:
	name: mutation-report
	path: reports/mutation/
	retention-days: 30

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