forge: block after launch so the process cannot exit; log launch outcome

app.py

@@ -121,6 +121,15 @@ if __name__ == "__main__":
     # That Node proxy is what dies here (log: "Running on local URL ... with SSR (Node
     # proxy -> Python :7861)" then "Stopping Node.js server..."). Serving straight from
     # Python removes the extra process entirely.
-    demo.launch(server_name="0.0.0.0",
-                server_port=int(os.environ.get("PORT", 7860)),
-                ssr_mode=False)
+    print("launching (ssr_mode=False)...", flush=True)
+    try:
+        demo.launch(server_name="0.0.0.0",
+                    server_port=int(os.environ.get("PORT", 7860)),
+                    ssr_mode=False)
+    except BaseException as exc:
+        print("launch raised %s: %r" % (type(exc).__name__, exc), flush=True)
+    # If launch() returns instead of blocking, the interpreter exits and takes the
+    # server with it (observed: "Running on local URL" then BaseEventLoop.__del__
+    # noise, i.e. shutdown). Block so the process cannot end.
+    print("launch returned; blocking main thread", flush=True)
+    threading.Event().wait()