fix: preserve managed agent config during deserialization

[wingding12]

Summary

Fixes #1849

When deserializing an agent with managed agents via from_dict(), the parent agent's **kwargs were being incorrectly passed to child agents. This caused child agent configurations (especially additional_authorized_imports) to be overwritten by the parent's configuration.

Root Cause

In MultiStepAgent.from_dict(), line 1043:

managed_agent = agent_class.from_dict(managed_agent_dict, **kwargs)

The **kwargs contains the parent agent's code_agent_kwargs (including additional_authorized_imports), which then overrides the child agent's own serialized configuration in CodeAgent.from_dict().

Fix

Remove **kwargs from the managed agent deserialization call:

managed_agent = agent_class.from_dict(managed_agent_dict)

Each managed agent should use only its own serialized configuration, not inherit the parent's kwargs.

Test Plan

• Added test_from_dict_preserves_managed_agent_authorized_imports that:
  • Creates a managed agent with custom additional_authorized_imports=["sympy"]
  • Creates a parent agent WITHOUT sympy
  • Serializes and deserializes via to_dict()/from_dict()
  • Verifies the managed agent retains sympy in its authorized_imports
• Test fails without the fix (NOP check verified)
• All existing serialization tests pass