fix: reject class-typed embedders at serialize time, drop unused validator

lib/crewai/src/crewai/knowledge/knowledge.py

@@ -70,40 +70,20 @@ def _serialize_embedder_spec(value: Any) -> dict[str, Any] | None:
         return None
     if isinstance(value, BaseEmbeddingsProvider):
         return value.model_dump(mode="json")
-    if isinstance(value, type) and issubclass(value, BaseEmbeddingsProvider):
-        return {"provider_class": f"{value.__module__}.{value.__qualname__}"}
     if isinstance(value, dict):
         return value
+    if isinstance(value, type) and issubclass(value, BaseEmbeddingsProvider):
+        raise TypeError(
+            f"Cannot checkpoint embedder class {value.__module__}.{value.__qualname__}: "
+            "build_embedder requires an instance or ProviderSpec dict, not a class. "
+            "Instantiate the provider before assigning it to Knowledge.embedder."
+        )
     raise TypeError(
         f"Cannot serialize embedder of type {type(value).__name__}: "
-        "expected ProviderSpec dict, BaseEmbeddingsProvider instance, or subclass."
+        "expected ProviderSpec dict or BaseEmbeddingsProvider instance."
     )
 
 
-def _validate_embedder_spec(value: Any) -> Any:
-    """Resolve provider_class dotted-path dicts back to a class on restore."""
-    if isinstance(value, dict) and set(value.keys()) == {"provider_class"}:
-        from crewai.types.callback import _trusted_deserialize
-
-        if not _trusted_deserialize():
-            raise ValueError(
-                f"Refusing to resolve embedder provider_class "
-                f"{value['provider_class']!r}: set "
-                "CREWAI_DESERIALIZE_CALLBACKS=1 to allow. Only enable this "
-                "for trusted checkpoint data."
-            )
-        from crewai.types.callback import _resolve_dotted_path
-
-        cls = _resolve_dotted_path(value["provider_class"])
-        if not isinstance(cls, type) or not issubclass(cls, BaseEmbeddingsProvider):
-            raise ValueError(
-                f"provider_class {value['provider_class']!r} did not resolve to a "
-                "BaseEmbeddingsProvider subclass."
-            )
-        return cls
-    return value
-
-
 class Knowledge(BaseModel):
     """
     Knowledge is a collection of sources and setup for the vector store to save and query relevant context.
@@ -121,7 +101,6 @@ class Knowledge(BaseModel):
     storage: KnowledgeStorage | None = Field(default=None)
     embedder: Annotated[
         EmbedderConfig | None,
-        BeforeValidator(_validate_embedder_spec),
         PlainSerializer(
             _serialize_embedder_spec, return_type=dict | None, when_used="json"
         ),