Crate behest_event 

Event types, EventActions, and the Hook system for the behest agent runtime.

This crate provides:

• AgentEvent: the canonical 17-variant event covering the full agent lifecycle (moved here from behest::runtime::event).
• EventActions: side-effect declarations that accompany events.
• Hook: single-method observer that returns Vec<EventActions>.
• HookStack: ordered dispatch of multiple hooks.

Design

Hooks use a single-method pattern (inspired by Rig): one on_event() method receives an AgentEvent and returns Vec<EventActions>. Adding new event types never requires changing the Hook trait signature.

Structs

ApprovalRequest

A request for human approval of a tool call.

CacheMetrics

Emitted after each model call when the provider reported prompt cache statistics. All fields are zero when the provider did not report cache hits or writes for this call.

CompactionCircuitOpened

Emitted when the compaction circuit breaker opens due to repeated failures.

ContextBuilt

Emitted after context has been assembled from session history and adapters.

DoomLoopDetected

Emitted when the agent is detected to be in a repetitive tool call cycle.

EventActions

Side-effect declarations associated with an event.

HookStack

An ordered stack of hooks.

MessageCommitted

Notification that a message has been persisted to the session store.

ModelStarted

Emitted when a model invocation begins, carrying iteration count.

ProgressEvent

A progress event emitted during tool execution or other long-running ops.

RunCancelled

Terminal event emitted when a run is cancelled before completion.

RunCompleted

Terminal event emitted when a run finishes successfully.

RunFailed

Terminal event emitted when a run terminates with an error.

RunStarted

Emitted when a run begins execution after session load and input admission.

TextDelta

Streaming text delta emitted during model response generation.

ToolCallCompleted

Emitted when the model finishes emitting a complete tool call.

ToolCallDelta

Streaming delta for tool call arguments during model response.

ToolCallStarted

Emitted when the model requests a tool call.

ToolExecutionFinished

Emitted when a tool function completes, carrying the result and duration.

ToolExecutionStarted

Emitted when a tool function begins executing.

UsageRecorded

Emitted after each model invocation to record token consumption.

Enums

AgentEvent

Event emitted during agent runtime execution.

ToolExecutionResult

Result of a single tool execution.

Traits

Hook

An observer hook that reacts to events.