def update_preference(
    preference_key: str, 
    preference_value: str, 
    tool_context: ToolContext
) -> Dict[str, Any]:
    """Update or add a user preference to the session state.

    Args:
        preference_key: The preference name (e.g., 'favorite_color', 'favorite_food')
        preference_value: The new preference value
        tool_context: Automatically injected by ADK

    Returns:
        dict: Operation status and updated preferences
    """
    # Get current preferences or initialize empty dict
    preferences = tool_context.state.get("preferences", {})

    # Update the specific preference
    preferences[preference_key] = preference_value

    # Save back to state
    tool_context.state["preferences"] = preferences

    return {
        "status": "success",
        "message": f"Updated {preference_key} to {preference_value}",
        "updated_preferences": preferences,
        "updated_at": datetime.now().isoformat()
    }

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