fix: Fix Pydantic Schema Generation Error for ClientSession

Problem: The test test_openapi_json_schema_accessible was failing because Pydantic couldn't generate a JSON schema for mcp.client.session.ClientSession, which is part of genai_types.ToolListUnion.

Root Cause: The AgentDetails model in src/google/adk/evaluation/app_details.py:37 had tool_declarations: genai_types.ToolListUnion, and ToolListUnion includes mcp.client.session.ClientSession which doesn't have Pydantic core schema support. This model is used in the FastAPI app through EvalCase → Invocation → AppDetails → AgentDetails, causing OpenAPI schema generation to fail.

Solution: Changed the type annotation from genai_types.ToolListUnion to list[Any] in two places:

AgentDetails.tool_declarations
_ToolDeclarations.tool_declarations

This allows Pydantic to generate the OpenAPI schema while maintaining runtime compatibility (the field still accepts the same values).

Co-authored-by: Xiang (Sean) Zhou <seanzhougoogle@google.com>
PiperOrigin-RevId: 863765002

Author: seanzhougoogle

src/google/adk/evaluation/app_details.py

@@ -14,6 +14,8 @@
 
 from __future__ import annotations
 
+from typing import Any
+
 from google.genai import types as genai_types
 from pydantic import Field
 
@@ -32,8 +34,12 @@ class AgentDetails(EvalBaseModel):
   instructions: str = Field(default="")
   """The instructions set on the Agent."""
 
-  tool_declarations: genai_types.ToolListUnion = Field(default_factory=list)
-  """A list of tools available to the Agent."""
+  tool_declarations: list[Any] = Field(default_factory=list)
+  """A list of tools available to the Agent.
+
+  At runtime, this contains elements of type genai_types.ToolListUnion.
+  We use list[Any] for Pydantic schema generation compatibility.
+  """
 
 
 class AppDetails(EvalBaseModel):

src/google/adk/evaluation/llm_as_judge_utils.py

@@ -16,6 +16,7 @@
 
 import enum
 import statistics
+from typing import Any
 from typing import Optional
 from typing import Union
 
@@ -78,7 +79,7 @@ def get_average_rubric_score(
 class _ToolDeclarations(EvalBaseModel):
   """Internal data model used for serializing Tool declarations."""
 
-  tool_declarations: dict[str, genai_types.ToolListUnion]
+  tool_declarations: dict[str, list[Any]]
 
 
 def get_tool_declarations_as_json_str(