feat(core-realtime): scaffold realtime optional core

Generator-emitted scaffold (pnpm turbo gen core-package realtime) plus
the story-00-precedent coverage repairs (coverage provider devDep,
symbols.ts exclude + tested allowlist mirror) and three minimal tests
covering generator-emitted realtime code the template suite misses.
Squash of 31d85e0 + review-fix cf11b38.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016j8z4VHjedXDTjEDNg7qHK

packages/core-eslint/base.js

@@ -8,6 +8,8 @@ import conformancePlugin from "./plugin.js";
 import path from "node:path";
 import { fileURLToPath } from "node:url";
 // <gen:realtime-rules-imports>
+import noDirectSocketIO from "./rules/no-direct-socket-io.js";
+import noRealtimeHandlerReexport from "./rules/no-realtime-handler-reexport.js";
 
 const __dirname = path.dirname(fileURLToPath(import.meta.url));
 const repoRoot = path.resolve(__dirname, "..", "..");
@@ -82,6 +84,8 @@ export default [
         { type: "tooling", pattern: "packages/core-testing" },
         { type: "core-composition", pattern: "packages/core-api" },
         { type: "core-composition", pattern: "packages/core-cms" },
+        { type: "core", pattern: "packages/core-realtime", mode: "folder" },
+
         { type: "core", pattern: "packages/core-*" },
         { type: "feature", pattern: "packages/!(core-*)" },
       ],
@@ -245,4 +249,19 @@ export default [
   // no-realtime-handler-reexport) are added here when @repo/core-realtime is
   // scaffolded via `pnpm turbo gen core-package realtime`.
   // <gen:realtime-rules>
+  {
+    files: ["**/*.{ts,tsx,mjs,cjs,js}"],
+    plugins: {
+      "repo-rules": {
+        rules: {
+          "no-direct-socket-io": noDirectSocketIO,
+          "no-realtime-handler-reexport": noRealtimeHandlerReexport,
+        },
+      },
+    },
+    rules: {
+      "repo-rules/no-direct-socket-io": "error",
+      "repo-rules/no-realtime-handler-reexport": "error",
+    },
+  },
 ];