Run full pipeline in a single GPU call

Fold preprocessing into generate() so one button click triggers one
@spaces.GPU acquisition instead of two (one on image change, one on
generate). The preprocessed preview now updates after generation.

app.py

@@ -86,23 +86,17 @@ def _viewer_iframe(ply_path: Path) -> str:
 # ----------------------------------------------------------------------------
 
 @spaces.GPU
-def on_image_change(image):
-    """Run preprocessing as soon as the input changes — gives the user instant
-    feedback on the matte/crop without waiting for the full generation."""
-    if image is None:
-        return None
-    return PIPE.preprocess_image(image)
-
-
-@spaces.GPU
-def generate(prepared, seed: int, steps: int, guidance_scale: float,
+def generate(image, seed: int, steps: int, guidance_scale: float,
              num_gaussians: int, output_format: str,
              progress=gr.Progress(track_tqdm=True)):
-    if prepared is None:
-        raise gr.Error("Please upload an image and wait for preprocessing to finish.")
+    """Run the full pipeline (preprocess + encode + sample + decode) in a
+    single GPU acquisition."""
+    if image is None:
+        raise gr.Error("Please upload an image first.")
 
     progress(0, desc="Generating...")
     t0 = time.time()
+    prepared = PIPE.preprocess_image(image)
     gen = torch.Generator(device=PIPE._device).manual_seed(int(seed))
     cond = PIPE.encode_image(prepared, generator=gen)
     out  = PIPE.sample_latent(cond, steps=int(steps),
@@ -127,7 +121,7 @@ def generate(prepared, seed: int, steps: int, guidance_scale: float,
 
     info = (f"{gaussian.get_xyz.shape[0]:,} gaussians  ·  "
             f"generation: {gen_dt:.1f}s  ·  saved: {download_path.name}")
-    return _viewer_iframe(ply_path), gr.update(value=str(download_path), interactive=True), info
+    return prepared, _viewer_iframe(ply_path), gr.update(value=str(download_path), interactive=True), info
 
 
 # ----------------------------------------------------------------------------
@@ -176,16 +170,10 @@ with gr.Blocks(title="TripoSplat") as demo:
             viewer_out = gr.HTML(value=PLACEHOLDER_HTML, label="Spark.js viewer")
             file_out = gr.DownloadButton(label="Download", value=None, interactive=False)
 
-    image_in.change(
-        fn=on_image_change,
-        inputs=[image_in],
-        outputs=[prepared_out],
-    )
-
     run_btn.click(
         fn=generate,
-        inputs=[prepared_out, seed_in, steps_in, cfg_in, num_g_in, fmt_in],
-        outputs=[viewer_out, file_out, info_out],
+        inputs=[image_in, seed_in, steps_in, cfg_in, num_g_in, fmt_in],
+        outputs=[prepared_out, viewer_out, file_out, info_out],
     )