feishu extension: tighten reply target fallback semantics

(cherry picked from commit f85ec610f267020b66713c09e648ec004b2e26f1)

extensions/feishu/src/outbound.test.ts

@@ -155,6 +155,26 @@ describe("feishuOutbound.sendText local-image auto-convert", () => {
       }),
     );
   });
+
+  it("falls back to threadId when replyToId is empty on sendText", async () => {
+    await sendText({
+      cfg: {} as any,
+      to: "chat_1",
+      text: "hello",
+      replyToId: " ",
+      threadId: "om_thread_2",
+      accountId: "main",
+    } as any);
+
+    expect(sendMessageFeishuMock).toHaveBeenCalledWith(
+      expect.objectContaining({
+        to: "chat_1",
+        text: "hello",
+        replyToMessageId: "om_thread_2",
+        accountId: "main",
+      }),
+    );
+  });
 });
 
 describe("feishuOutbound.sendText replyToId forwarding", () => {
@@ -327,5 +347,13 @@ describe("feishuOutbound.sendMedia renderMode", () => {
         accountId: "main",
       }),
     );
+    expect(sendMessageFeishuMock).toHaveBeenCalledWith(
+      expect.objectContaining({
+        to: "chat_1",
+        text: "caption",
+        replyToMessageId: "om_thread_1",
+        accountId: "main",
+      }),
+    );
   });
 });