ci: upload an inspectable coverage report as a build artifact

.github/workflows/node.js.yml

@@ -24,3 +24,18 @@ jobs:
             - run: npm run format:check
             - run: npm test
             - run: npm run coverage:check
+            # Uploaded from one matrix leg only — the report is identical across them, and
+            # two legs writing the same artifact name is an error. Makes a coverage
+            # regression inspectable from the failing run instead of only reproducible locally.
+            - name: Upload coverage report
+              if: matrix.node-version == '22.x'
+              uses: actions/upload-artifact@v7
+              with:
+                  name: coverage-report
+                  # Only the readable report. `coverage/` also holds c8's raw V8 dump in
+                  # tmp/, which is ~97% of the bytes and inspectable by nothing — 23 MB of
+                  # tmp against a 647 kB report in the worst case here.
+                  path: |
+                      coverage/lcov-report
+                      coverage/lcov.info
+                  retention-days: 14

package.json

@@ -23,6 +23,10 @@
         "coverage:check": "c8 --check-coverage npm test"
     },
     "c8": {
+        "reporter": [
+            "text",
+            "lcov"
+        ],
         "include": [
             "telegrambot/**/*.js"
         ],