feat(core-eslint): rule no-direct-socket-io

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/core-eslint/base.js

@@ -4,6 +4,7 @@ import tseslint from "typescript-eslint";
 import turboPlugin from "eslint-plugin-turbo";
 import boundaries from "eslint-plugin-boundaries";
 import globals from "globals";
+import noDirectSocketIO from "./rules/no-direct-socket-io.js";
 
 export default [
   { ignores: ["dist/**", "node_modules/**", ".next/**", ".turbo/**", "storybook-static/**"] },
@@ -169,4 +170,13 @@ export default [
       ],
     },
   },
+  // R2 — `socket.io` and `socket.io-client` must not be imported outside
+  // core-realtime/src/ and apps/*/server.ts. Use @repo/core-realtime helpers.
+  {
+    files: ["**/*.{ts,tsx,mjs,cjs,js}"],
+    plugins: { "repo-rules": { rules: { "no-direct-socket-io": noDirectSocketIO } } },
+    rules: {
+      "repo-rules/no-direct-socket-io": "error",
+    },
+  },
 ];