Enum HookCallback 

#[non_exhaustive]
pub enum HookCallback {
    PreTurn(Box<dyn Fn(&PreTurnContext) -> HookResult + Send + Sync>),
    PostTurn(Box<dyn Fn(&PostTurnContext) + Send + Sync>),
    PreToolCallDecide(Box<dyn Fn(&PreToolCallDecideContext) -> HookResult + Send + Sync>),
    PostToolCall(Box<dyn Fn(&PostToolCallContext) + Send + Sync>),
    OnToolError(Box<dyn Fn(&OnToolErrorContext) -> Option<String> + Send + Sync>),
    OnSessionStart(Box<dyn Fn(&OnSessionStartContext) + Send + Sync>),
    OnSessionEnd(Box<dyn Fn(&OnSessionEndContext) + Send + Sync>),
    OnCompaction(Box<dyn Fn(&OnCompactionContext) + Send + Sync>),
    OnInteraction(Box<dyn Fn(&OnInteractionContext) -> HookResult + Send + Sync>),
    TransformToolInput(Box<dyn Fn(&PreToolCallDecideContext) -> Option<Value> + Send + Sync>),
}

A registered hook callback, keyed by hook point.

Each variant wraps a boxed closure that receives the strongly-typed context for that hook point. Mirroring the SDK’s hook contracts: PreTurn and PreToolCallDecide are deciding hooks that return a HookResult to allow or deny the turn / tool call; OnToolError is a transform hook that returns the error representation the model should see (None = use the harness’s default formatting); all other variants are fire-and-forget observers.

Variants (Non-exhaustive)

Non-exhaustive enums could have additional variants added in future. Therefore, when matching against variants of non-exhaustive enums, an extra wildcard arm must be added to account for any future variants.

PreTurn(Box<dyn Fn(&PreTurnContext) -> HookResult + Send + Sync>)

Callback invoked before each agent turn.

Returns a HookResult so it can allow or deny the turn before the model runs (SDK PreTurnHook, a DecideHook[Content]).

PostTurn(Box<dyn Fn(&PostTurnContext) + Send + Sync>)

Callback invoked after each agent turn completes.

PreToolCallDecide(Box<dyn Fn(&PreToolCallDecideContext) -> HookResult + Send + Sync>)

Callback invoked before deciding whether to execute a tool call.

PostToolCall(Box<dyn Fn(&PostToolCallContext) + Send + Sync>)

Callback invoked after a tool call completes.

OnToolError(Box<dyn Fn(&OnToolErrorContext) -> Option<String> + Send + Sync>)

Callback invoked when a tool call produces an error.

Returns the error representation the model should see, or None to let the harness use its default error formatting (SDK OnToolErrorHook, a TransformHook[Exception, Any]).

OnSessionStart(Box<dyn Fn(&OnSessionStartContext) + Send + Sync>)

Callback invoked when a new agent session begins.

OnSessionEnd(Box<dyn Fn(&OnSessionEndContext) + Send + Sync>)

Callback invoked when an agent session ends.

OnCompaction(Box<dyn Fn(&OnCompactionContext) + Send + Sync>)

Callback invoked when conversation history is compacted.

OnInteraction(Box<dyn Fn(&OnInteractionContext) -> HookResult + Send + Sync>)

Callback invoked on each interaction event.

TransformToolInput(Box<dyn Fn(&PreToolCallDecideContext) -> Option<Value> + Send + Sync>)

Transform tool input arguments before execution.

The closure receives the pre-tool-call context and may return Some(new_args) to replace the tool arguments, or None to leave them unchanged. Multiple transform hooks are applied sequentially — each receives the (possibly already-modified) arguments from the previous transform.

Trait Implementations

impl Debug for HookCallback

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.