fix(invariants): replay histories and pack companions

packages/todo/tool-todo/tests/invariant.spec.ts

@@ -1,12 +1,13 @@
 import { describe, expect, it } from 'vitest'
 import { Context } from 'cordis'
-import type { Session, SessionEvent } from '@deepseek-ai/dsh-session'
+import SessionStore, { type Session, type SessionEvent } from '@deepseek-ai/dsh-session'
 import * as TodoInvariant from '@deepseek-ai/dsh-tool-todo/invariant'
 import InvariantService from '@deepseek-ai/dsh-invariants'
 
 async function setup(): Promise<Context> {
   const ctx = new Context()
-  await ctx.plugin(InvariantService)
+  await ctx.plugin(SessionStore)
+  await ctx.plugin(InvariantService, { enabled: true })
   await ctx.plugin(TodoInvariant)
   return ctx
 }
@@ -50,4 +51,18 @@ describe('todo snapshot invariants', () => {
       })
     }).not.toThrow()
   })
+
+  it('rejects an invalid existing snapshot on late registration', async () => {
+    const ctx = new Context()
+    await ctx.plugin(SessionStore)
+    ctx.sessions.create().append('todo/write', {
+      todos: [
+        { content: 'duplicate', status: 'pending' },
+        { content: 'duplicate', status: 'completed' },
+      ],
+    })
+    await ctx.plugin(InvariantService, { enabled: true })
+
+    await expect(ctx.plugin(TodoInvariant).then(() => undefined)).rejects.toThrow(/repeats content "duplicate"/)
+  })
 })