[Weight-adapter/Trainer] Bypass forward mode in Weight adapter system (#11958)

* Add API of bypass forward module

* bypass implementation

* add bypass fwd into nodes list/trainer

comfy/sd.py

@@ -20,6 +20,7 @@ import comfy.ldm.ace.vae.music_dcae_pipeline
 import comfy.ldm.hunyuan_video.vae
 import comfy.ldm.mmaudio.vae.autoencoder
 import comfy.pixel_space_convert
+import comfy.weight_adapter
 import yaml
 import math
 import os
@@ -101,6 +102,105 @@ def load_lora_for_models(model, clip, lora, strength_model, strength_clip):
     return (new_modelpatcher, new_clip)
 
 
+def load_bypass_lora_for_models(model, clip, lora, strength_model, strength_clip):
+    """
+    Load LoRA in bypass mode without modifying base model weights.
+
+    Instead of patching weights, this injects the LoRA computation into the
+    forward pass: output = base_forward(x) + lora_path(x)
+
+    Non-adapter patches (bias diff, weight diff, etc.) are applied as regular patches.
+
+    This is useful for training and when model weights are offloaded.
+    """
+    key_map = {}
+    if model is not None:
+        key_map = comfy.lora.model_lora_keys_unet(model.model, key_map)
+    if clip is not None:
+        key_map = comfy.lora.model_lora_keys_clip(clip.cond_stage_model, key_map)
+
+    logging.debug(f"[BypassLoRA] key_map has {len(key_map)} entries")
+
+    lora = comfy.lora_convert.convert_lora(lora)
+    loaded = comfy.lora.load_lora(lora, key_map)
+
+    logging.debug(f"[BypassLoRA] loaded has {len(loaded)} entries")
+
+    # Separate adapters (for bypass) from other patches (for regular patching)
+    bypass_patches = {}  # WeightAdapterBase instances -> bypass mode
+    regular_patches = {}  # diff, set, bias patches -> regular weight patching
+
+    for key, patch_data in loaded.items():
+        if isinstance(patch_data, comfy.weight_adapter.WeightAdapterBase):
+            bypass_patches[key] = patch_data
+        else:
+            regular_patches[key] = patch_data
+
+    logging.debug(f"[BypassLoRA] {len(bypass_patches)} bypass adapters, {len(regular_patches)} regular patches")
+
+    k = set()
+    k1 = set()
+
+    if model is not None:
+        new_modelpatcher = model.clone()
+
+        # Apply regular patches (bias diff, weight diff, etc.) via normal patching
+        if regular_patches:
+            patched_keys = new_modelpatcher.add_patches(regular_patches, strength_model)
+            k.update(patched_keys)
+
+        # Apply adapter patches via bypass injection
+        manager = comfy.weight_adapter.BypassInjectionManager()
+        model_sd_keys = set(new_modelpatcher.model.state_dict().keys())
+
+        for key, adapter in bypass_patches.items():
+            if key in model_sd_keys:
+                manager.add_adapter(key, adapter, strength=strength_model)
+                k.add(key)
+            else:
+                logging.warning(f"[BypassLoRA] Adapter key not in model state_dict: {key}")
+
+        injections = manager.create_injections(new_modelpatcher.model)
+
+        if manager.get_hook_count() > 0:
+            new_modelpatcher.set_injections("bypass_lora", injections)
+    else:
+        new_modelpatcher = None
+
+    if clip is not None:
+        new_clip = clip.clone()
+
+        # Apply regular patches to clip
+        if regular_patches:
+            patched_keys = new_clip.add_patches(regular_patches, strength_clip)
+            k1.update(patched_keys)
+
+        # Apply adapter patches via bypass injection
+        clip_manager = comfy.weight_adapter.BypassInjectionManager()
+        clip_sd_keys = set(new_clip.cond_stage_model.state_dict().keys())
+
+        for key, adapter in bypass_patches.items():
+            if key in clip_sd_keys:
+                clip_manager.add_adapter(key, adapter, strength=strength_clip)
+                k1.add(key)
+
+        clip_injections = clip_manager.create_injections(new_clip.cond_stage_model)
+        if clip_manager.get_hook_count() > 0:
+            new_clip.patcher.set_injections("bypass_lora", clip_injections)
+    else:
+        new_clip = None
+
+    for x in loaded:
+        if (x not in k) and (x not in k1):
+            patch_data = loaded[x]
+            patch_type = type(patch_data).__name__
+            if isinstance(patch_data, tuple):
+                patch_type = f"tuple({patch_data[0]})"
+            logging.warning(f"NOT LOADED: {x} (type={patch_type})")
+
+    return (new_modelpatcher, new_clip)
+
+
 class CLIP:
     def __init__(self, target=None, embedding_directory=None, no_init=False, tokenizer_data={}, parameters=0, state_dict=[], model_options={}):
         if no_init: