fix(feedback): address backend review gaps

packages/feedback/message-feedback/tests/invariant.spec.ts

@@ -0,0 +1,23 @@
+import { describe, expect, it } from 'vitest'
+import InvariantService from '@deepseek-ai/dsh-invariants'
+import * as MessageFeedbackInvariant from '../src/invariant.ts'
+import { setupHarness } from './helpers.ts'
+
+describe('message-feedback invariant companion', () => {
+  it('removes its registry contribution when its fiber is disposed (HMR safety)', async () => {
+    const harness = await setupHarness()
+    try {
+      await harness.ctx.plugin(InvariantService)
+      const fiber = await harness.ctx.plugin(MessageFeedbackInvariant)
+
+      expect(() => {
+        harness.ctx.invariants.register('@deepseek-ai/dsh-message-feedback', () => {})
+      }).toThrow(/already registered/u)
+
+      await fiber.dispose()
+      await expect(harness.ctx.plugin(MessageFeedbackInvariant).await()).resolves.toBeDefined()
+    } finally {
+      await harness.dispose()
+    }
+  })
+})