refactor: identify and freeze messages at creation

packages/core/agent-loop/tests/tool-order.spec.ts

@@ -1,3 +1,4 @@
+import { createUserMessage } from '@deepseek-ai/dsh-llm'
 /**
  * Loop-level tool-order determinism: the request/header event — and therefore the frozen
  * request the adapter receives — carries the assembly's canonical tool order (system-prompt's
@@ -58,7 +59,7 @@ async function runTurn(registrationOrder: string[], toolOrder?: SystemPromptConf
   const ctx = await harness(adapter, toolOrder)
   for (const name of registrationOrder) registerNamed(ctx, name)
   const agent = ctx.agentLoop.create(SessionId('a1'), { provider: 'mock', model: 'mock' })
-  agent.followup({ content: [{ type: 'text', text: 'go' }], source: { kind: 'user' } })
+  agent.followup(createUserMessage({ content: [{ type: 'text', text: 'go' }], source: { kind: 'user' } }))
   await waitForIdle(ctx, agent)
   return { ctx, agent, adapter }
 }
@@ -102,7 +103,7 @@ describe('loop-level canonical tool order', () => {
       if (error instanceof Error) errors.push(error)
     })
     const agent = ctx.agentLoop.create(SessionId('a1'), { provider: 'mock', model: 'mock' })
-    agent.followup({ content: [{ type: 'text', text: 'go' }], source: { kind: 'user' } })
+    agent.followup(createUserMessage({ content: [{ type: 'text', text: 'go' }], source: { kind: 'user' } }))
     await waitForIdle(ctx, agent)
     expect(adapter.requests).toHaveLength(0)
     expect(errors.map(e => e.message)).toEqual(['toolOrder lists unregistered tool "ghost"; known tools: alpha'])