fix(agent-runtime): set isResume based on thread message history (#419)

## Summary

- 修复 `ensureThread` 中 `isResume` 的判断逻辑：当传入 `threadId` 但 thread
中没有历史消息时（如通过 `createThread` 刚创建的空 thread），`isResume` 应为 `false`
- 通过 `store.getThread()` 检查 `thread.messages.length > 0` 来决定 `isResume`
的值
- 更新测试用例，覆盖空 thread 和有历史消息的 thread 两种场景

## Test plan

- [x] 原有测试 "should set isResume=false when no threadId provided" 通过
- [x] 修改测试 "should set isResume=false when threadId provided but thread
has no messages" 通过
- [x] 新增测试 "should set isResume=true when threadId provided and thread
has messages" 通过
- [x] 全部 104 个测试通过

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: jerryliang64

core/agent-runtime/src/AgentRuntime.ts

@@ -80,7 +80,9 @@ export class AgentRuntime {
 
   private async ensureThread(input: CreateRunInput): Promise<{ threadId: string; input: CreateRunInput }> {
     if (input.threadId) {
-      return { threadId: input.threadId, input: { ...input, isResume: true } };
+      const thread = await this.store.getThread(input.threadId);
+      const isResume = thread.messages.length > 0;
+      return { threadId: input.threadId, input: { ...input, isResume } };
     }
     const thread = await this.store.createThread();
     return { threadId: thread.id, input: { ...input, threadId: thread.id, isResume: false } };

core/agent-runtime/test/AgentRuntime.test.ts

@@ -249,7 +249,7 @@ describe('test/AgentRuntime.test.ts', () => {
       assert.equal(capturedInput!.isResume, false);
     });
 
-    it('should set isResume=true when threadId provided', async () => {
+    it('should set isResume=false when threadId provided but thread has no messages', async () => {
       let capturedInput: CreateRunInput | undefined;
       executor.execRun = async function* (input: CreateRunInput): AsyncGenerator<AgentStreamMessage> {
         capturedInput = input;
@@ -261,6 +261,26 @@ describe('test/AgentRuntime.test.ts', () => {
         threadId: thread.id,
         input: { messages: [{ role: 'user', content: 'Hi' }] },
       });
+      assert.equal(capturedInput!.isResume, false);
+    });
+
+    it('should set isResume=true when threadId provided and thread has messages', async () => {
+      let capturedInput: CreateRunInput | undefined;
+      executor.execRun = async function* (input: CreateRunInput): AsyncGenerator<AgentStreamMessage> {
+        capturedInput = input;
+        yield { message: { role: MessageRole.Assistant, content: [{ type: 'text', text: 'hi' }] } };
+      };
+
+      // First run creates thread with messages
+      const result = await runtime.syncRun({
+        input: { messages: [{ role: 'user', content: 'Hi' }] },
+      });
+
+      // Second run on the same thread — now it has history
+      await runtime.syncRun({
+        threadId: result.threadId,
+        input: { messages: [{ role: 'user', content: 'Hello again' }] },
+      });
       assert.equal(capturedInput!.isResume, true);
     });