fix(bgm): hot-reload game definition edits

Invalidate the virtual bgm module on changes under the games root so
editing a definition reloads the page instead of requiring a manual
refresh.

packages/bgm/src/vite.ts

@@ -16,7 +16,7 @@
  * hot-reloads the app via `addWatchFile`.
  */
 import * as path from 'node:path';
-import type { Plugin } from 'vite';
+import type { ModuleNode, Plugin } from 'vite';
 import { collectPackages, loadDefs } from './collect.js';
 import type { Package, SerializedPackage } from './types.js';
 
@@ -52,6 +52,18 @@ export function bgm(options: BgmOptions): Plugin {
       if (id === PACKAGES) return VIRTUAL_PREFIX + PACKAGES;
       if (id.startsWith(PACKAGE)) return VIRTUAL_PREFIX + id;
     },
+    handleHotUpdate(ctx) {
+      // Re-collect and invalidate the virtual modules when a game definition
+      // changes, so edits hot-reload instead of requiring a manual refresh.
+      if (!ctx.file.startsWith(root)) return;
+      const invalidated: ModuleNode[] = [];
+      const mod = ctx.server.moduleGraph.getModuleById(VIRTUAL_PREFIX + PACKAGES);
+      if (mod) {
+        ctx.server.moduleGraph.invalidateModule(mod);
+        invalidated.push(mod);
+      }
+      return invalidated;
+    },
     load(id) {
       if (!id.startsWith(VIRTUAL_PREFIX)) return;
       const virtual = id.slice(VIRTUAL_PREFIX.length);