Restore _to_safe_string in LazyConfig.save_yaml, plus minor VLM/transformers tweaks

- lazy_config/lazy.py: re-add _to_safe_string so callable _target_ values are
  emitted as importable dotted paths in config.yaml. Without this, save_yaml's
  fallback `str(value)` produced "<class '...'>" / "<function ... at 0x...>"
  strings that break downstream consumers like export_model.
- configs/base/defaults/vlm.py: add VLMConfig.safetensors_path for loading a
  safetensors checkpoint from a different folder than model_name.
- utils/vfm/monkey_patch.py: loosen _EXPECTED_TRANSFORMERS_VERSION from exact
  "4.57.1" to "4.57." prefix so patch-version bumps don't trip the guard.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: yy-code-nv

cosmos_framework/configs/base/defaults/vlm.py

@@ -136,6 +136,9 @@ class VLMConfig:
     # HuggingFace model identifier or local path. Drives AutoConfig + AutoModel selection.
     model_name: str = ""
 
+    # Safetensor path for model for load a safetensor from different folder 
+    safetensors_path: str = ""
+
     # Optional pretrained-weights overlay (separate from the AutoModel structural
     # init driven by model_name).
     pretrained_weights: PretrainedWeightsConfig = PretrainedWeightsConfig()

cosmos_framework/utils/lazy_config/lazy.py

@@ -321,6 +321,26 @@ def is_serializable(item):
             except Exception as e:
                 return False
 
+        # For classes / functions / bound methods we want the importable dotted
+        # path, not `repr(obj)` — the latter yields strings like
+        # `<class 'cosmos.X'>` or `<function f at 0x…>` which break any
+        # downstream consumer that calls hydra.utils.instantiate on the loaded
+        # YAML (e.g. cosmos.scripts.export_model).
+        from cosmos_framework.utils.lazy_config.registry import convert_target_to_string
+
+        def _to_safe_string(value):
+            # Preserve primitives — `str(True)` is the literal string `"True"`,
+            # which yaml then quotes and downstream consumers parse as a string
+            # instead of the original bool/int/float.
+            if isinstance(value, (bool, int, float, str)) or value is None:
+                return value
+            try:
+                if callable(value):
+                    return convert_target_to_string(value)
+            except Exception:
+                pass
+            return str(value)
+
         # Function to convert unserializable items to strings
         def serialize_config(config):
             if isinstance(config, DictConfig):
@@ -338,14 +358,14 @@ def serialize_config(config):
                         serialize_config(value)
                     else:
                         if not is_serializable(value) and value is not None:
-                            config[key] = str(value)
+                            config[key] = _to_safe_string(value)
             elif isinstance(config, ListConfig):
                 for i, item in enumerate(config):
                     if isinstance(item, (DictConfig, ListConfig)):
                         serialize_config(item)
                     else:
                         if not is_serializable(item) and item is not None:
-                            config[i] = str(item)
+                            config[i] = _to_safe_string(item)
             else:
                 raise NotImplementedError("Input config must be a DictConfig or ListConfig.")
             return config

cosmos_framework/utils/vfm/monkey_patch.py

@@ -13,7 +13,7 @@
 
 from cosmos_framework.utils import log
 
-_EXPECTED_TRANSFORMERS_VERSION = "4.57.1"
+_EXPECTED_TRANSFORMERS_VERSION = "4.57."
 
 
 def patch_qwen3_vl_forward(model):