fix: forward reference resolution in Pydantic schema generation.

PiperOrigin-RevId: 831019476

Author: shawn-yang-google

vertexai/_genai/_agent_engines_utils.py

@@ -590,6 +590,9 @@ def _is_pydantic_serializable(param: inspect.Parameter) -> bool:
  if param.annotation == inspect.Parameter.empty:
  return True
 
+ if "ForwardRef" in repr(param.annotation):
+ return True
+
  if isinstance(param.annotation, str):
  return False
 
@@ -641,7 +644,12 @@ def _generate_schema(
  name: (
  # 1. We infer the argument type here: use Any rather than None so
  # it will not try to auto-infer the type based on the default value.
- (param.annotation if param.annotation != inspect.Parameter.empty else Any),
+ (
+ param.annotation
+ if param.annotation != inspect.Parameter.empty
+ and "ForwardRef" not in repr(param.annotation)
+ else Any
+ ),
  pydantic.Field(
  # 2. We do not support default values for now.
  # default=(