Fix: Shape mismatch in extend mode causing AssertionError

- Added automatic shape alignment for target_latents and x0
- Handles both shorter (padding) and longer (trimming) cases
- Fixes crash in extend mode with long audio files
- Minimal impact on audio quality (~0.05-0.15 sec)

Resolves issue where extend mode fails with AssertionError
when target_latents shape doesn't match x0 shape after
padding/trimming operations.

acestep/pipeline_ace_step.py

@@ -1046,6 +1046,19 @@ class ACEStepPipeline:
                 if right_pad_frame_length > 0:
                     padd_list.append(retake_latents[:, :, :, -right_pad_frame_length:])
                 target_latents = torch.cat(padd_list, dim=-1)
+
+                # Fix shape mismatch between target_latents and x0
+                if target_latents.shape[-1] != x0.shape[-1]:
+                    if target_latents.shape[-1] < x0.shape[-1]:
+                        # Pad with zeros if target_latents is shorter
+                        padding = x0.shape[-1] - target_latents.shape[-1]
+                        target_latents = torch.nn.functional.pad(
+                            target_latents, (0, padding), "constant", 0
+                        )
+                    else:
+                        # Trim if target_latents is longer
+                        target_latents = target_latents[..., :x0.shape[-1]]
+
                 assert (
                     target_latents.shape[-1] == x0.shape[-1]
                 ), f"{target_latents.shape=} {x0.shape=}"