Address code review: add round-trip decode assertion, expand content validation tests

Agent-Logs-Url: https://github.com/objectstack-ai/spec/sessions/fc1d7caa-ef41-4b0b-9ce4-267c262596b4

Co-authored-by: xuyushun441-sys <255036401+xuyushun441-sys@users.noreply.github.com>

Author: Copilot

packages/services/service-ai/src/__tests__/ai-service.test.ts

@@ -623,12 +623,26 @@ describe('AI Routes', () => {
     const routes = buildAIRoutes(service, service.conversationService, silentLogger);
     const chatRoute = routes.find(r => r.path === '/api/v1/ai/chat')!;
 
+    // Numeric content should be rejected
     const response = await chatRoute.handler({
       body: { messages: [{ role: 'user', content: 123 }] },
     });
-
     expect(response.status).toBe(400);
     expect((response.body as any).error).toContain('content');
+
+    // Object content (not an array) should be rejected
+    const response2 = await chatRoute.handler({
+      body: { messages: [{ role: 'user', content: { nested: true } }] },
+    });
+    expect(response2.status).toBe(400);
+    expect((response2.body as any).error).toContain('content');
+
+    // Boolean content should be rejected
+    const response3 = await chatRoute.handler({
+      body: { messages: [{ role: 'user', content: true }] },
+    });
+    expect(response3.status).toBe(400);
+    expect((response3.body as any).error).toContain('content');
   });
 
   it('POST /api/v1/ai/conversations/:id/messages should return 400 for invalid role', async () => {

packages/services/service-ai/src/__tests__/vercel-stream-encoder.test.ts

@@ -19,6 +19,10 @@ describe('encodeStreamPart', () => {
     const frame = encodeStreamPart(part);
     expect(frame).toBe(`0:${JSON.stringify('say "hi"\nnewline')}\n`);
     expect(frame.startsWith('0:')).toBe(true);
+
+    // Verify round-trip: decode the frame payload back to the original text
+    const decoded = JSON.parse(frame.slice(2).trim());
+    expect(decoded).toBe('say "hi"\nnewline');
   });
 
   it('should encode tool-call as "9:" frame', () => {