refactor: identify and freeze messages at creation

packages/subagent/subagent-spawn/tests/spawn.e2e.ts

@@ -1,3 +1,4 @@
+import { createUserMessage } from '@deepseek-ai/dsh-llm'
 import { mkdtemp, readFile, rm } from 'node:fs/promises'
 import { tmpdir } from 'node:os'
 import { join } from 'node:path'
@@ -24,10 +25,11 @@ describe.skipIf(!process.env.DEEPSEEK_API_KEY)('spawn backend with-key smoke', (
     ctx = await spawnHarness(workdir)
     const parent = ctx.agentLoop.create(SessionId('e2e-parent'), { provider: 'deepseek', model: 'deepseek-v4-flash' })
 
-    parent.followup({ content: [{ type: 'text', text:
+    parent.followup(createUserMessage({
+      content: [{ type: 'text', text:
       'Use the subagent tool to delegate this exact task: "Use the bash tool to write the text '
       + 'SUBAGENT_WAS_HERE into a file named proof.txt in the current directory." '
-      + 'After the subagent finishes, tell me it is done.' }], source: { kind: 'user' } })
+      + 'After the subagent finishes, tell me it is done.' }], source: { kind: 'user' } }))
     await waitForIdle(ctx, parent)
 
     // Assert the filesystem effect independently of the model response.

packages/subagent/subagent-spawn/tests/subagent-spawn.spec.ts

@@ -1,3 +1,4 @@
+import { createUserMessage } from '@deepseek-ai/dsh-llm'
 import { describe, expect, it } from 'vitest'
 import { Context, symbols, type EffectMeta } from 'cordis'
 import Loader from '@cordisjs/plugin-loader'
@@ -106,7 +107,7 @@ describe('dsh-subagent-spawn', () => {
   it('a fresh child does NOT inherit the parent conversation (its log starts empty before the prompt)', async () => {
     // Drive the parent through one real turn so it has history, THEN spawn.
     const { ctx, parent } = await setup([textResponse('parent turn'), textResponse('child sees nothing')])
-    parent.followup({ content: [{ type: 'text', text: 'parent prompt' }], source: { kind: 'user' } })
+    parent.followup(createUserMessage({ content: [{ type: 'text', text: 'parent prompt' }], source: { kind: 'user' } }))
     await parent.whenIdle()
     const parentEventCount = parent.session.events.length
     expect(parentEventCount).toBeGreaterThan(0)
@@ -383,7 +384,7 @@ describe('dsh-subagent-spawn', () => {
         textResponse('parent answer'),
         textResponse('child answer'),
       ])
-      parent.followup({ content: [{ type: 'text', text: 'hi' }], source: { kind: 'user' } })
+      parent.followup(createUserMessage({ content: [{ type: 'text', text: 'hi' }], source: { kind: 'user' } }))
       await parent.whenIdle()
 
       const run = await start(ctx, 'spawn', {