fix: resolve pydantic violation.

Author: lingxi-at-contextual

src/contextual/types/agent_metadata_response.py

@@ -40,6 +40,9 @@ class GetTwilightAgentResponse(BaseModel):
     """Description of the agent"""
 
 
-AgentMetadataResponse: TypeAlias = Union["AgentMetadata", GetTwilightAgentResponse]
-
 from .agent_metadata import AgentMetadata
+
+# Made a one-time change here to import the AgentMetadata before union, instead of using forward reference.
+# Forward reference here violates the Pydantic type system, so it doesn't quite work.
+# If there is any issue (circular import, etc) regarding this in the future, we can then find another solution.
+AgentMetadataResponse: TypeAlias = Union[AgentMetadata, GetTwilightAgentResponse]