Module callbacks 

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 Callback type aliases for agent, model, and tool lifecycle hooks.

Structs

EventsCompactionConfig

Configuration for automatic context compaction.

Enums

BeforeModelResult

Result from a BeforeModel callback

Traits

BaseEventsSummarizer

Trait for summarizing events during context compaction.

Type Aliases

AfterAgentCallback

Callback invoked after an agent completes. Return Ok(Some(content)) to override.

AfterModelCallback

Callback invoked after a model call. Return Ok(Some(response)) to override.

AfterToolCallback

Callback invoked after a tool executes. Return Ok(Some(content)) to override the result.

AfterToolCallbackFull

Rich after-tool callback that receives the tool, arguments, and response.

BeforeAgentCallback

Callback invoked before an agent runs. Return Ok(Some(content)) to short-circuit.

BeforeModelCallback

Callback invoked before a model call. Can modify the request or skip the call entirely.

BeforeToolCallback

Callback invoked before a tool executes. Return Ok(Some(content)) to skip execution.

GlobalInstructionProvider

Alias for InstructionProvider used at the global (runner) level.

InstructionProvider

Async function that generates dynamic instructions from context.

OnToolErrorCallback

Callback invoked when a tool execution fails (after retries are exhausted).