ci: add code coverage integration

Add go-test-coverage for coverage threshold enforcement. Coverage data
is uploaded as artifacts on main branch and compared against baseline
in PRs using shell script that gracefully handles first run without
baseline. PR comments show coverage percentage.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.gitea/workflows/ci.yaml

@@ -17,6 +17,61 @@ jobs:
       - name: Run tests
         run: go test -race -coverprofile=coverage.txt ./...
 
+      - name: Check coverage
+        uses: vladopajic/go-test-coverage@v2
+        with:
+          config: ./.testcoverage.yml
+
+      # Download baseline coverage from main branch (for PRs)
+      - name: Download baseline coverage
+        if: gitea.event_name == 'pull_request'
+        uses: actions/download-artifact@v3
+        with:
+          name: coverage-baseline
+          path: ./baseline
+        continue-on-error: true
+
+      # Compare coverage against baseline (for PRs)
+      - name: Compare coverage
+        if: gitea.event_name == 'pull_request'
+        run: |
+          CURRENT=$(go tool cover -func=coverage.txt | grep "^total:" | awk '{print $NF}' | tr -d '%')
+          if [ -f ./baseline/coverage.txt ]; then
+            BASE=$(go tool cover -func=./baseline/coverage.txt | grep "^total:" | awk '{print $NF}' | tr -d '%')
+            echo "Base coverage: ${BASE}%"
+            echo "Current coverage: ${CURRENT}%"
+            if [ "$(echo "$CURRENT < $BASE" | bc -l)" -eq 1 ]; then
+              echo "::error::Coverage decreased from ${BASE}% to ${CURRENT}%"
+              exit 1
+            fi
+            echo "Coverage maintained or improved: ${BASE}% -> ${CURRENT}%"
+          else
+            echo "No baseline coverage found, skipping comparison"
+            echo "Current coverage: ${CURRENT}%"
+          fi
+
+      # Upload coverage as baseline (only on main)
+      - name: Upload coverage baseline
+        if: gitea.ref == 'refs/heads/main'
+        uses: actions/upload-artifact@v3
+        with:
+          name: coverage-baseline
+          path: coverage.txt
+          retention-days: 90
+
+      # Post coverage to PR comment
+      - name: Post coverage comment
+        if: gitea.event_name == 'pull_request'
+        env:
+          GITEA_TOKEN: ${{ secrets.GITEA_TOKEN }}
+          GITEA_URL: ${{ gitea.server_url }}
+        run: |
+          COVERAGE=$(go tool cover -func=coverage.txt | grep "^total:" | awk '{print $NF}')
+          curl -X POST "${GITEA_URL}/api/v1/repos/${{ gitea.repository }}/issues/${{ gitea.event.pull_request.number }}/comments" \
+            -H "Authorization: token ${GITEA_TOKEN}" \
+            -H "Content-Type: application/json" \
+            -d "{\"body\": \"## Coverage Report\n\nTotal coverage: **${COVERAGE}**\"}"
+
   vulnerabilities:
     runs-on: ubuntu-latest
     steps:

.testcoverage.yml

@@ -0,0 +1,13 @@
+# Coverage configuration for go-test-coverage
+# https://github.com/vladopajic/go-test-coverage
+
+profile: coverage.txt
+
+threshold:
+  file: 0
+  package: 0
+  total: 0
+
+exclude:
+  paths:
+    - _test\.go$