Struct HookEvent 

pub struct HookEvent {
    pub kind: HookKind,
    pub tool_name: Option<String>,
    pub tool_runtime_name: Option<String>,
    pub tool_input: Option<Value>,
    pub tool_output: Option<String>,
    pub message: Option<String>,
    pub session_id: Option<String>,
    pub transcript: Option<Vec<Value>>,
    pub data: Value,
}

A hook event payload dispatched to extension handlers.

Fields are optional and populated only when relevant to the hook kind:

Kind	tool_name	tool_input	tool_output	message	session_id
before_tool_call	✓	✓
after_tool_call	✓	✓	✓
before_message				✓
on_message_complete				✓
on_compaction				✓	✓
on_session_start					✓
on_session_end					✓

The data field is available on all events for extensions that need to attach arbitrary structured context when constructing synthetic events.

Fields

kind: HookKind

Which hook fired.

tool_name: Option<String>

Tool name for tool-specific hooks; None for general hooks. This is the API-safe name (sanitized for the LLM).

tool_runtime_name: Option<String>

Original runtime name of the tool (before API sanitization). Extension authors typically write runtime names in their manifests.

tool_input: Option<Value>

Tool input arguments for before_tool_call and after_tool_call.

tool_output: Option<String>

Tool output for after_tool_call.

message: Option<String>

LLM message content for before_message.

session_id: Option<String>

Session identifier for session lifecycle hooks.

transcript: Option<Vec<Value>>

Session message history for on_session_end. Contains the conversation transcript so extensions (like Stelline) can extract memories without reaching into runtime internals.

data: Value

Arbitrary extension-defined data, passed through without inspection.

Implementations

impl HookEvent

pub fn before_tool_call(tool_name: &str, input: Value) -> Self

Construct a before_tool_call event.

pub fn after_tool_call(tool_name: &str, input: Value, output: String) -> Self

Construct an after_tool_call event carrying both input and output. Output is truncated to MAX_HOOK_OUTPUT_SIZE to prevent sending megabytes of bash output over the JSON-RPC pipe.

pub fn before_message(message: &str) -> Self

Construct a before_message event.

pub fn on_message_complete(message: &str, data: Value) -> Self

Construct an on_message_complete event.

pub fn on_compaction( old_session_id: &str, new_session_id: &str, summary: &str, message_count: usize, data: Value, ) -> Self

Construct an on_compaction event.

pub fn on_session_start(session_id: &str) -> Self

Construct an on_session_start event.

pub fn on_session_end(session_id: &str, transcript: Option<Vec<Value>>) -> Self

Construct an on_session_end event.

impl HookEvent

pub fn with_runtime_name(self, name: &str) -> Self

Set the runtime name for tool-related events.

Trait Implementations

impl Clone for HookEvent

fn clone(&self) -> HookEvent

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for HookEvent

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

Formats the value using the given formatter.

impl<'de> Deserialize<'de> for HookEvent

fn deserialize<__D>(__deserializer: __D) -> Result<Self, __D::Error>

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl Serialize for HookEvent

fn serialize<__S>(&self, __serializer: __S) -> Result<__S::Ok, __S::Error>

where __S: Serializer,

Serialize this value into the given Serde serializer.