Struct HookStack 

pub struct HookStack<M>
where
    M: CompletionModel,
{ /* private fields */ }

An ordered list of hooks run as one hook.

Each hook is consulted in registration order. How their Flow results combine depends on the event (see the module docs): CompletionCall patches accumulate; ToolCall / ToolResult rewrites chain; every other event uses first non-Continue wins. Because the runner is fail-closed, a non-Continue action always takes effect or terminates the run — it is never silently ignored. An empty stack is the no-op hook and observes nothing, so the runner skips event dispatch for it entirely.

This is the default hook type carried by an Agent and an AgentRunner; build one with add_hook.

Implementations

impl<M> HookStack<M>

where M: CompletionModel,

pub fn new() -> Self

An empty stack (the no-op hook).

pub fn with<H>(hook: H) -> Self

where H: AgentHook<M> + 'static,

A stack containing a single hook.

pub fn push<H>(&mut self, hook: H)

where H: AgentHook<M> + 'static,

Append a hook to the end of the stack.

pub fn is_empty(&self) -> bool

Whether the stack contains no hooks.

pub fn len(&self) -> usize

Number of hooks in the stack.

Trait Implementations

impl<M> AgentHook<M> for HookStack<M>

where M: CompletionModel,

fn observes(&self, kind: StepEventKind) -> bool

The stack observes an event kind if any of its hooks does (so an empty stack observes nothing).

async fn on_event(&self, ctx: &HookContext, event: StepEvent<'_, M>) -> Flow

Called at every observable point of the agent run (subject to observes). Receives the run-scoped HookContext and the StepEvent. The default implementation is a no-op: it ignores every event and returns Flow::Continue. It does not narrow observes (which defaults to true), so a hook that takes this default is still dispatched every event — override observes to skip the high-frequency delta events. (The () no-op hook overrides observes to false, so the runner skips dispatching those delta events to it; it still receives, and returns Flow::Continue for, every other event.)

impl<M> Clone for HookStack<M>

where M: CompletionModel,

fn clone(&self) -> Self

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<M> Debug for HookStack<M>

where M: CompletionModel,

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

Formats the value using the given formatter.

impl<M> Default for HookStack<M>

where M: CompletionModel,

fn default() -> Self

Returns the “default value” for a type.