优化聊天框输入聚焦逻辑，增强网络错误处理

src/lib/chatStream.test.ts

@@ -97,4 +97,18 @@ describe("streamCopilotChat", () => {
       { type: "error", message: "Login expired. Please sign in again.", detail: undefined },
     ]);
   });
+
+  it("emits network error when fetch throws", async () => {
+    apiFetch.mockRejectedValue(new TypeError("Failed to fetch"));
+
+    const events: Array<{ type: string; message?: string; detail?: string }> = [];
+    await streamCopilotChat({
+      message: "hi",
+      onEvent: (event) => events.push(event),
+    });
+
+    expect(events).toEqual([
+      { type: "error", message: "network request failed", detail: "Failed to fetch" },
+    ]);
+  });
 });