ci: add pull request validation workflow

.github/copilot-instructions.md

@@ -20,7 +20,7 @@ The extension has no activation code. Changes to a snippet catalog take effect t
 
 ## Commands
 
-There are no npm scripts, automated tests, or lint configuration. There is consequently no single-test command.
+There are no npm scripts, automated tests, or lint configuration. The PR workflow mirrors these local validation commands:
 
 ```bash
 # Install the locked packaging dependency
@@ -33,7 +33,11 @@ node -e "for (const f of ['snippets/snippets.json','snippets/jinja-snippets.json
 npx vsce package
 ```
 
-`npx vsce package` creates a `.vsix` file in the repository root; it is ignored by Git. The release workflow runs this same packaging command with Node.js 20.
+`npx vsce package` creates a `.vsix` file in the repository root; it is ignored by Git. The PR workflow runs the same commands on Node.js 20, and the release workflow uses `npx vsce package` for tag publishes.
+
+## Pull request checks
+
+PRs should keep the snippet catalogs parseable and the package manifest valid. The CI workflow runs `npm ci`, JSON parsing for all three snippet catalogs, and `npx vsce package` on every pull request.
 
 ## Releases
 

.github/workflows/ci.yml

@@ -0,0 +1,27 @@
+name: PR CI
+
+on:
+  pull_request:
+
+jobs:
+  validate:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v7
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v7
+        with:
+          node-version: '20'
+          cache: 'npm'
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Validate snippet catalogs
+        run: node -e "for (const f of ['snippets/snippets.json','snippets/jinja-snippets.json','snippets/django-snippets.json']) JSON.parse(require('fs').readFileSync(f, 'utf8'))"
+
+      - name: Package extension
+        run: npx vsce package

README.md

@@ -171,6 +171,16 @@ Found a bug? Want a new snippet? Contributions are welcome!
 2. **Request Features**: Have an idea? Share it!
 3. **Submit PRs**: Fork, code, and submit a pull request
 
+### Continuous Integration
+
+Every pull request runs a small validation suite on Node.js 20:
+
+1. `npm ci`
+2. Parse all snippet catalogs as JSON
+3. `npx vsce package`
+
+If you want to mirror CI locally before opening a PR, run the same commands from the repository root.
+
 ### Suggesting New Snippets
 
 When requesting a new snippet, please include: