fix(runtime-vapor): update app instance on root hmr reload

packages/runtime-vapor/__tests__/hmr.spec.ts

@@ -216,6 +216,44 @@ describe('hot module replacement', () => {
     expect(root.innerHTML).toBe(`<div>app-injected</div>`)
   })
 
+  test('reload root vapor component should update app instance for unmount', async () => {
+    const root = document.createElement('div')
+    const appId = 'test-root-reload-app-unmount'
+    const oldUnmountSpy = vi.fn()
+    const newUnmountSpy = vi.fn()
+
+    const App = defineVaporComponent({
+      __hmrId: appId,
+      setup() {
+        onUnmounted(oldUnmountSpy)
+      },
+      render: () => template(`<div>old</div>`)(),
+    })
+    createRecord(appId, App as any)
+
+    const app = createVaporApp(App)
+    app.mount(root)
+    expect(root.innerHTML).toBe(`<div>old</div>`)
+
+    reload(appId, {
+      __vapor: true,
+      __hmrId: appId,
+      setup() {
+        onUnmounted(newUnmountSpy)
+      },
+      render: () => template(`<div>new</div>`)(),
+    })
+
+    await nextTick()
+    expect(root.innerHTML).toBe(`<div>new</div>`)
+    expect(oldUnmountSpy).toHaveBeenCalledTimes(1)
+
+    app.unmount()
+    await nextTick()
+    expect(root.innerHTML).toBe(``)
+    expect(newUnmountSpy).toHaveBeenCalledTimes(1)
+  })
+
   test('failed rerender restores current instance and warning context', () => {
     const root = document.createElement('div')
     const id = 'test-rerender-restore-context'

packages/runtime-vapor/src/hmr.ts

@@ -65,6 +65,13 @@ export function hmrReload(
   }
   mountComponent(newInstance, parent, anchor)
 
+  if (!parentInstance) {
+    const app = instance.appContext.app
+    if (app && app._instance === instance) {
+      app._instance = newInstance
+    }
+  }
+
   updateParentBlockOnHmrReload(parentInstance, instance, newInstance)
   updateParentTeleportOnHmrReload(instance, newInstance)
 }