test(shared): property tests + scoped StrykerJS mutation testing (#417, #418)

.github/workflows/mutation.yml

@@ -0,0 +1,74 @@
+name: Mutation Testing
+
+on:
+  pull_request:
+    branches: [main]
+  schedule:
+    - cron: '0 6 * * *'
+
+concurrency:
+  group: mutation-${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+permissions:
+  contents: read
+
+jobs:
+  incremental:
+    name: Incremental (per-PR, report-only)
+    if: github.event_name == 'pull_request'
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v7
+
+      - uses: actions/setup-node@v6
+        with:
+          node-version: 22
+          cache: npm
+
+      - run: npm ci
+
+      - name: Restore Stryker incremental report
+        uses: actions/cache@v4
+        with:
+          path: packages/shared/reports/stryker-incremental.json
+          key: stryker-incremental-${{ github.run_id }}
+          restore-keys: stryker-incremental-
+
+      - name: Run mutation testing (incremental)
+        working-directory: packages/shared
+        run: npm run mutation
+
+      - name: Upload mutation report
+        if: always()
+        uses: actions/upload-artifact@v4
+        with:
+          name: mutation-report-pr
+          path: packages/shared/reports/mutation/
+
+  nightly:
+    name: Nightly (full scope, report)
+    if: github.event_name == 'schedule'
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v7
+
+      - uses: actions/setup-node@v6
+        with:
+          node-version: 22
+          cache: npm
+
+      - run: npm ci
+
+      - name: Run mutation testing (full scope)
+        working-directory: packages/shared
+        run: npm run mutation
+
+      - name: Upload mutation report
+        if: always()
+        uses: actions/upload-artifact@v4
+        with:
+          name: mutation-report-nightly
+          path: packages/shared/reports/mutation/

.gitignore

@@ -33,6 +33,11 @@ Thumbs.db
 # Coverage
 coverage/
 
+# Mutation testing (StrykerJS)
+.stryker-tmp/
+packages/shared/.stryker-tmp/
+packages/shared/reports/
+
 # Playwright smoke (apps/web/e2e)
 apps/web/e2e/.auth/
 apps/web/e2e/.report/