Add PR comments for code coverage reporting

Use github-script action to post coverage percentage and threshold
status as PR comments. Updates existing comment on subsequent pushes
to avoid duplicate comments.

Added: PR comments showing code coverage percentage and threshold status

Author: saturnflyer

.github/workflows/test.yml

@@ -64,6 +64,62 @@ jobs:
           name: coverage-report
           path: coverage/
           retention-days: 30
+      - name: Comment Coverage on PR
+        if: github.event_name == 'pull_request' && always()
+        uses: actions/github-script@v7
+        with:
+          script: |
+            const fs = require('fs');
+
+            if (!fs.existsSync('coverage/.last_run.json')) {
+              console.log('Coverage report not found');
+              return;
+            }
+
+            const coverage = JSON.parse(fs.readFileSync('coverage/.last_run.json', 'utf8'));
+            const coveragePercent = coverage.result.line;
+            const threshold = 50;
+            const meetsThreshold = coveragePercent >= threshold;
+            const emoji = meetsThreshold ? '✅' : '⚠️';
+
+            const comment = `## ${emoji} Code Coverage Report
+
+            **Coverage:** ${coveragePercent}%
+            **Threshold:** ${threshold}%
+
+            ${emoji} Coverage ${meetsThreshold ? 'meets' : 'is below'} minimum threshold
+
+            <sub>📊 [View detailed coverage report in artifacts](${context.payload.repository.html_url}/actions/runs/${context.runId})</sub>`;
+
+            // Find existing coverage comment
+            const { data: comments } = await github.rest.issues.listComments({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              issue_number: context.issue.number,
+            });
+
+            const botComment = comments.find(comment =>
+              comment.user.type === 'Bot' &&
+              comment.body.includes('Code Coverage Report')
+            );
+
+            if (botComment) {
+              // Update existing comment
+              await github.rest.issues.updateComment({
+                owner: context.repo.owner,
+                repo: context.repo.repo,
+                comment_id: botComment.id,
+                body: comment
+              });
+            } else {
+              // Create new comment
+              await github.rest.issues.createComment({
+                owner: context.repo.owner,
+                repo: context.repo.repo,
+                issue_number: context.issue.number,
+                body: comment
+              });
+            }
 
   linter:
     name: Linter