debug: remove queue=False and add pre-dispatch print

app.py

@@ -351,13 +351,19 @@ with gr.Blocks(delete_cache=(43200, 43200), theme=custom_theme) as demo:
         outputs=[is_samimage, single_sam_image_example, single_image_example],
     )
 
+    def _preprocess_image_dispatch(img, rmbg):
+        import sys, os
+        print(f"[ZGPU] upload handler ENTER pid={os.getpid()}", flush=True)
+        sys.stdout.flush()
+        out = preprocess_image_fn(img, rmbg, _enable_pre_resize_default)
+        print("[ZGPU] upload handler RETURN", flush=True)
+        sys.stdout.flush()
+        return out
+
     image_prompt.upload(
-        lambda img, rmbg: preprocess_image_fn(
-            img, rmbg, _enable_pre_resize_default
-        ),
+        _preprocess_image_dispatch,
         inputs=[image_prompt, rmbg_tag],
         outputs=[image_prompt, raw_image_cache],
-        queue=False,
     ).success(
         active_btn_by_content,
         inputs=image_prompt,