perf(ci): move full mutation sweeps off the release path

Keep fresh coverage and both real mutation preflights required in every CI tier. Run complete canonical sweeps daily or manually in isolated jobs with distinct reports, retained failure diagnostics, and explicit report-presence checks.

Preserve regression inventories, release qualification and mutation settings; remove the superseded duplicate gate test. Related: #3281.

.github/workflows/ci.yml

@@ -267,14 +267,10 @@ jobs:
       - name: Run reverse tools tests with coverage
         run: npm run test:coverage:reverse-tools
       - name: Preflight both reverse tools mutation configurations
-        if: needs.changes.outputs.tier == 'fast'
         run: |
           node scripts/prepare-reverse-tools-mutation.mjs
           npx --no-install stryker run stryker.config.mjs --dryRunOnly
           npx --no-install stryker run stryker.semantics.config.mjs --dryRunOnly
-      - name: Report complete reverse tools mutation results
-        if: needs.changes.outputs.tier == 'full'
-        run: npm run test:mutation:reverse-tools
       - name: Retain available reverse tools diagnostics
         if: ${{ !cancelled() }}
         uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4.6.2

.github/workflows/mutation.yml

@@ -0,0 +1,62 @@
+name: Mutation sweep
+
+on:
+  schedule:
+    - cron: "47 4 * * *"
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+concurrency:
+  group: mutation-${{ github.ref }}
+  cancel-in-progress: false
+
+env:
+  HUSKY: "0"
+
+jobs:
+  mutation:
+    name: Mutation sweep (${{ matrix.suite }})
+    runs-on: ubuntu-latest
+    timeout-minutes: 60
+    strategy:
+      fail-fast: false
+      max-parallel: 2
+      matrix:
+        include:
+          - suite: reverse-tools
+            config: stryker.config.mjs
+          - suite: reverse-tools-semantics
+            config: stryker.semantics.config.mjs
+    steps:
+      - uses: actions/checkout@11d5960a326750d5838078e36cf38b85af677262 # v4.4.0
+      - uses: actions/setup-node@49933ea5288caeca8642d1e84afbd3f7d6820020 # v4.4.0
+        with:
+          node-version-file: .nvmrc
+      - name: Cache npm package downloads
+        uses: ./.github/actions/npm-cache
+      - run: npm ci
+      - run: npm run test:prepare
+      - name: Run the complete configuration
+        env:
+          MUTATION_CONFIG: ${{ matrix.config }}
+        run: |
+          node scripts/prepare-reverse-tools-mutation.mjs
+          npx --no-install stryker run "${MUTATION_CONFIG}"
+      - name: Require both reports from the completed sweep
+        env:
+          REPORT_BASE: reports/mutation/${{ matrix.suite }}
+        run: |
+          test -s "${REPORT_BASE}.json"
+          test -s "${REPORT_BASE}.html"
+      - name: Retain available mutation diagnostics
+        if: ${{ !cancelled() }}
+        uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4.6.2
+        with:
+          name: mutation-${{ matrix.suite }}-${{ github.run_attempt }}
+          path: |
+            reports/mutation/${{ matrix.suite }}.json
+            reports/mutation/${{ matrix.suite }}.html
+          if-no-files-found: warn
+          retention-days: 7