Constant TOOL_PROGRESS_CALL_ID_KEY 

pub const TOOL_PROGRESS_CALL_ID_KEY: &'static str;

Core traits and types.

Always available regardless of feature flags. Includes:

• Agent - The fundamental trait for all agents
• Tool / Toolset - For extending agents with capabilities
• Session / State - For managing conversation context
• Event - For streaming agent responses
• AdkError / Result - Unified error handling Event-level provider_metadata key carrying the originating tool’s function-call id on a tool-progress event.