ci: comment test coverage

.github/workflows/test-coverage.yml

@@ -0,0 +1,68 @@
+name: Test Coverage
+
+on:
+  pull_request:
+    branches: [ main ]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: '20'
+          cache: 'npm'
+
+      - name: Install dependencies
+        run: npm install
+
+      - name: Run tests with coverage
+        run: |
+          npm run test:coverage > coverage-output.txt 2>&1
+
+      - name: Upload coverage report
+        uses: actions/upload-artifact@v4
+        with:
+          name: coverage-report
+          path: coverage-output.txt
+          retention-days: 1
+
+  comment:
+    runs-on: ubuntu-latest
+    needs: test
+    permissions:
+      pull-requests: write
+
+    steps:
+      - name: Download coverage report
+        uses: actions/download-artifact@v4
+        with:
+          name: coverage-report
+
+      - name: Read coverage report
+        id: coverage
+        run: |
+          echo "COVERAGE_REPORT<<EOF" >> $GITHUB_OUTPUT
+          cat coverage-output.txt >> $GITHUB_OUTPUT
+          echo "EOF" >> $GITHUB_OUTPUT
+
+      - name: Post coverage comment
+        uses: peter-evans/create-or-update-comment@v5
+        with:
+          issue-number: ${{ github.event.pull_request.number }}
+          body: |
+            ## Test Coverage Report
+
+            ```
+            ${{ steps.coverage.outputs.COVERAGE_REPORT }}
+            ```
+
+            ---
+            *Coverage report generated by GitHub Actions*