test(session): cover preparation disposal directly

packages/core/session/tests/preparation.spec.ts

@@ -0,0 +1,21 @@
+import { describe, expect, it, vi } from 'vitest'
+import { Session, SessionId, SessionPreparation } from '@deepseek-ai/dsh-session'
+
+describe('SessionPreparation', () => {
+  it('retains the exact Session and releases provider state only once', () => {
+    const session = Session.create(SessionId('prepared'))
+    const release = vi.fn()
+    {
+      using preparation = SessionPreparation.create(session, { release })
+      expect(preparation.session).toBe(session)
+      preparation[Symbol.dispose]()
+      expect(release).toHaveBeenCalledOnce()
+    }
+    expect(release).toHaveBeenCalledOnce()
+  })
+
+  it('disposes a preparation without provider state', () => {
+    using preparation = SessionPreparation.create(Session.create(SessionId('unretained')))
+    expect(() => { preparation[Symbol.dispose]() }).not.toThrow()
+  })
+})