fix: preserve reasoning in short-term memory replay

src/core/agent-reasoning-memory.test.ts

@@ -0,0 +1,32 @@
+import { describe, expect, it } from 'vitest';
+import { toModelMessages } from './agent.js';
+
+describe('assistant reasoning is preserved in replayed short-term memory', () => {
+  it('replays assistant reasoning alongside assistant text when available', () => {
+    const messages = toModelMessages([
+      { id: 'user-1', role: 'user', content: 'hello', timestamp: 1 },
+      { id: 'assistant-1', role: 'assistant', content: 'world', reasoning: 'think-step', timestamp: 2 },
+    ]);
+
+    expect(messages).toEqual([
+      { role: 'user', content: 'hello' },
+      {
+        role: 'assistant',
+        content: [
+          { type: 'reasoning', text: 'think-step' },
+          { type: 'text', text: 'world' },
+        ],
+      },
+    ]);
+  });
+
+  it('keeps assistant messages as plain text when no reasoning exists', () => {
+    const messages = toModelMessages([
+      { id: 'assistant-1', role: 'assistant', content: 'plain reply', timestamp: 1 },
+    ]);
+
+    expect(messages).toEqual([
+      { role: 'assistant', content: 'plain reply' },
+    ]);
+  });
+});