Add Primer Brand MCP server

.changeset/heading-usage-guidance.md

@@ -0,0 +1,5 @@
+---
+'@primer/react-brand': patch
+---
+
+Added inert JSDoc annotations to the `Heading` component's `as` and `size` props clarifying that `as` sets only the semantic heading level while `size` controls the visual size.

.changeset/primer-brand-mcp.md

@@ -0,0 +1,22 @@
+---
+'@primer/brand-mcp': minor
+---
+
+Added `@primer/brand-mcp`, a Model Context Protocol (MCP) server that helps AI agents use Primer Brand correctly when building GitHub marketing and landing pages.
+
+It exposes version-aware tools like `primer_brand_component`, `primer_brand_examples`, `primer_brand_tokens`, `primer_brand_asset`, `primer_brand_docs`, and `primer_brand_review`, which read the `@primer/react-brand` package installed in your project and validates generated JSX/CSS against known design system conventions during development (e.g. unknown components, invalid props, hardcoded values, off-brand patterns).
+
+Add it to your MCP client (e.g. Copilot CLI, in `~/.copilot/mcp-config.json`):
+
+```json
+{
+  "mcpServers": {
+    "primer-brand": {
+      "type": "local",
+      "command": "npx",
+      "args": ["@primer/brand-mcp@latest"],
+      "tools": ["*"]
+    }
+  }
+}
+```

.github/workflows/ci.yml

@@ -49,3 +49,6 @@ jobs:
 
       - name: Run unit tests
         run: npm run test
+
+      - name: Run MCP server smoke tests
+        run: npm run smoke --workspace=packages/mcp