validate API contracts in CI

.gitea/workflows/ci.yaml

@@ -9,4 +9,19 @@ jobs:
     runs-on: debian-latest
     steps:
       - uses: actions/checkout@v4
-      - run: test -f README.md && test -f AGENTS.md && test -f docs/versioning.md
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 22
+      - name: Validate repository documentation
+        run: test -f README.md && test -f AGENTS.md && test -f docs/versioning.md
+      - name: Validate JSON contracts and fixtures
+        run: |
+          node --input-type=module <<'NODE'
+          import { readdir, readFile } from 'node:fs/promises';
+          for (const directory of ['contracts/v1', 'fixtures/v1']) {
+            for (const name of await readdir(directory)) {
+              if (!name.endsWith('.json')) continue;
+              JSON.parse(await readFile(`${directory}/${name}`, 'utf8'));
+            }
+          }
+          NODE