Enum HookEvent 

#[non_exhaustive]
pub enum HookEvent<'a> {
    SessionStart {
        goal: &'a str,
    },
    PreToolCall {
        name: &'a str,
        args: &'a Value,
    },
    PostToolCall {
        name: &'a str,
        args: &'a Value,
        result: &'a str,
        duration_ms: u64,
    },
    PreCompact {
        transcript_len: usize,
    },
    PostCompact {
        removed: usize,
        summary_chars: usize,
    },
    SessionEnd {
        outcome: &'a RuntimeOutcome,
    },
    UserPromptSubmit {
        content: &'a str,
    },
    Stop {
        outcome: &'a RuntimeOutcome,
    },
    SubagentStart {
        goal: &'a str,
        depth: usize,
    },
    SubagentStop {
        outcome: &'a RuntimeOutcome,
        depth: usize,
    },
    PostToolCallFailure {
        name: &'a str,
        args: &'a Value,
        error: &'a str,
    },
    PermissionDenied {
        tool_name: &'a str,
        reason: &'a str,
    },
    Notification {
        message: &'a str,
    },
    Setup,
}

Events emitted at lifecycle points during an agent run.

This enum is #[non_exhaustive] — new variants may be added in future releases without a breaking change.

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.

SessionStart

Fired at the start of an agent run, before any LLM call.

Fields

goal: &'a str

The goal text passed to AgentRuntime::run().

PreToolCall

Fired before a tool is dispatched (after the permission hook).

Fields

name: &'a str

Name of the tool about to be called.

args: &'a Value

Arguments that will be passed to the tool.

PostToolCall

Fired after a tool returns.

Fields

name: &'a str

Name of the tool that was called.

args: &'a Value

Arguments that were passed to the tool.

result: &'a str

The result string returned by the tool (or error message).

duration_ms: u64

Wall-clock duration of the tool execution in milliseconds.

PreCompact

Fired before compaction is attempted.

Fields

transcript_len: usize

Current transcript length in characters.

PostCompact

Fired after compaction completes.

Fields

removed: usize

Number of messages removed during compaction.

summary_chars: usize

Character count of the summary message added.

SessionEnd

Fired at the end of an agent run, before returning.

Dispatched by AgentRuntime::run() after every turn completes.

Fields

outcome: &'a RuntimeOutcome

The outcome that will be returned.

UserPromptSubmit

Fired after the user submits a message, before the LLM processes it.

Fields

content: &'a str

The user’s input content.

Stop

Fired when the agent completes normally (NoMoreToolCalls).

Fields

outcome: &'a RuntimeOutcome

The final outcome.

SubagentStart

Fired before a sub-agent is dispatched.

Fields

goal: &'a str

The sub-agent’s goal text.

depth: usize

Nesting depth (0 = top-level).

SubagentStop

Fired after a sub-agent completes.

Fields

outcome: &'a RuntimeOutcome

The sub-agent’s outcome.

depth: usize

Nesting depth.

PostToolCallFailure

Fired when a tool call returns an error (before PostToolCall).

Fields

name: &'a str

Name of the tool that failed.

args: &'a Value

Arguments that were passed to the tool.

error: &'a str

The error message.

PermissionDenied

Fired when a permission check denies a tool call.

Fields

tool_name: &'a str

Name of the tool that was denied.

reason: &'a str

Human-readable reason for the denial.

Notification

Fired when the agent emits a notification to the user.

Fields

message: &'a str

Notification content.

Setup

Fired once at the very beginning, before SessionStart, for one-time setup.

Trait Implementations

impl<'a> Clone for HookEvent<'a>

fn clone(&self) -> Self

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl<'a> Debug for HookEvent<'a>

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

Formats the value using the given formatter.