K2 Latent Pin (outside regions)

Replaces everything outside the region union with a reference latent — hard spatial locality. Why this exists: token-gated regional LoRAs stop the DELTA at the box edge, but image-to-image attention stays continuous (on purpose — otherwise you get tile seams). A regional LoRA therefore still nudges the trajectory outside its box a little. Sample the same seed twice — once with and once without the regional LoRAs — and pin the outside to the clean run to remove that residual drift. feather_tokens softens the boundary in latent space; 0 is a hard cut.