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.

Currently only dispatched by the legacy Agent path (deleted in Goal 219). The AgentRuntime does not yet dispatch SessionEnd.

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) -> HookEvent<'a>

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.