Add spatial smoothing to remove latent grid artifacts

The per-element correction creates a visible mesh pattern at the VAE's
8x8 patch boundaries. A 3x3 box blur in latent space (24x24 pixels)
smooths adjacent corrections while preserving the large-scale
correction structure.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

nodes.py

@@ -1,4 +1,5 @@
 import torch
+import torch.nn.functional as F
 
 
 class SMCCFGCtrl:
@@ -101,6 +102,13 @@ class SMCCFGCtrl:
             phi = s.std().clamp(min=1e-6)
             u_sw = -K_eff * torch.tanh(s / phi)
 
+            # Spatial smoothing: the per-element correction creates a grid
+            # pattern at latent boundaries (each latent = 8x8 pixels). A mild
+            # 3x3 box blur in latent space removes these artifacts while
+            # preserving the large-scale correction structure.
+            if u_sw.ndim == 4:
+                u_sw = F.avg_pool2d(u_sw, kernel_size=3, stride=1, padding=1)
+
             # Corrected guidance error (in normalized noise space)
             guidance_eps = guidance_eps + u_sw