Python: make SerializationMixin.from_dict enforce the documented type check

python/packages/core/agent_framework/_serialization.py

@@ -535,8 +535,10 @@ async def get_current_weather(location: Annotated[str, "The city name"]) -> str:
         if dependencies is None:
             dependencies = {}
 
-        # Get the type identifier
-        type_id = cls._get_type_identifier(value)
+        # Resolve the expected identifier from the class, not the payload:
+        # reading it from `value` makes the mismatch check tautological, so
+        # any supplied 'type' would silently match itself.
+        type_id = cls._get_type_identifier()
 
         if (supplied_type := value.get("type")) and supplied_type != type_id:
             raise ValueError(f"Type mismatch: expected '{type_id}', got '{supplied_type}'")

python/packages/core/tests/core/test_serializable_mixin.py

@@ -5,6 +5,7 @@
 import logging
 from typing import Any
 
+import pytest
 from typing_extensions import Self
 
 from agent_framework._serialization import SerializationMixin
@@ -369,6 +370,26 @@ def __init__(self, value: str):
         out = obj.to_dict()
         assert out["type"] == "my_custom_type"
 
+    def test_from_dict_rejects_mismatched_type(self):
+        """from_dict raises ValueError when the payload type doesn't match the class."""
+
+        class TestClass(SerializationMixin):
+            def __init__(self, value: str):
+                self.value = value
+
+        with pytest.raises(ValueError, match="Type mismatch: expected 'test_class', got 'function_tool'"):
+            TestClass.from_dict({"type": "function_tool", "value": "x"})
+
+    def test_from_json_rejects_mismatched_type(self):
+        """from_json surfaces the same mismatch error instead of silently coercing."""
+
+        class TestClass(SerializationMixin):
+            def __init__(self, value: str):
+                self.value = value
+
+        with pytest.raises(ValueError, match="Type mismatch"):
+            TestClass.from_json('{"type": "some_other_type", "value": "x"}')
+
     def test_from_json(self):
         """Test from_json deserializes JSON string."""