Fix build error

app.py

@@ -6,7 +6,8 @@ from typing import Any, Dict, List, Optional
 
 from fastapi.responses import FileResponse, HTMLResponse, JSONResponse
 from fastapi.staticfiles import StaticFiles
-from gradio import Server
+from gradio import Blocks, Server
+from gradio.events import api as gradio_api
 
 from backend.config import (
     APP_TITLE,
@@ -215,6 +216,17 @@ async def serve_generated_file(session_id: str, kind: str, filename: str):
 app.mount("/static", StaticFiles(directory=str(FRONTEND_DIR)), name="frontend-static")
 
 
+def _build_demo() -> Blocks:
+    # Expose the launched Blocks at module scope so Gradio hot reload can find it.
+    with Blocks(mode="server") as demo:
+        for fn, api_kwargs in app._deferred_apis:
+            gradio_api(fn=fn, **api_kwargs)
+    return demo
+
+
+demo = _build_demo()
+
+
 def _port_is_available(port: int, host: str = "127.0.0.1") -> bool:
     with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as sock:
         sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
@@ -237,4 +249,4 @@ def _choose_server_port(preferred: int = 7860, attempts: int = 10) -> int:
 if __name__ == "__main__":
     server_port = _choose_server_port()
     print(f"Starting {APP_TITLE} on port {server_port}")
-    app.launch(server_name="0.0.0.0", server_port=server_port)
+    demo.launch(_app=app, server_name="0.0.0.0", server_port=server_port)

tests/test_app_startup.py

@@ -0,0 +1,15 @@
+import importlib
+import sys
+
+import gradio as gr
+
+
+def test_app_module_exposes_top_level_server_demo() -> None:
+    sys.modules.pop("app", None)
+
+    module = importlib.import_module("app")
+
+    assert isinstance(module.app, gr.Server)
+    assert hasattr(module, "demo")
+    assert isinstance(module.demo, gr.Blocks)
+    assert module.demo.mode == "server"