Module hooks 

Hooks System for A3S Code Agent

Provides a mechanism to intercept and customize agent behavior at various lifecycle points. Hooks can validate, transform, or block operations.

Hook Events

• PreToolUse: Before tool execution (can block/modify)
• PostToolUse: After tool execution (fire-and-forget)
• GenerateStart: Before LLM generation
• GenerateEnd: After LLM generation
• SessionStart: When session is created
• SessionEnd: When session is destroyed

Example

let engine = HookEngine::new();

// Register a hook
engine.register(Hook {
    id: "security-check".to_string(),
    event_type: HookEventType::PreToolUse,
    matcher: Some(HookMatcher::tool("Bash")),
    config: HookConfig::default(),
});

// Fire hook and get result
let result = engine.fire(HookEvent::PreToolUse { ... }).await;
match result {
    HookResult::Continue(None) => { /* proceed */ }
    HookResult::Continue(Some(modified)) => { /* proceed with modified data */ }
    HookResult::Block(reason) => { /* stop execution */ }
}

Structs

GenerateEndEvent

Generate end event payload

GenerateStartEvent

Generate start event payload

Hook

Hook definition

HookConfig

Hook configuration

HookEngine

Hook engine

HookMatcher

Hook matcher for filtering events

HookResponse

Response from a hook handler

OnErrorEvent

On-error event payload

PostResponseEvent

Post-response event payload (fired after LLM response is processed)

PostToolUseEvent

Post-tool-use event payload

PrePromptEvent

Pre-prompt event payload (fired before prompt augmentation)

PreToolUseEvent

Pre-tool-use event payload

SessionEndEvent

Session end event payload

SessionStartEvent

Session start event payload

SkillLoadEvent

Skill load event payload

SkillUnloadEvent

Skill unload event payload

TokenUsageInfo

Token usage information

ToolCallInfo

Tool call information

ToolResultData

Tool execution result data

Enums

ErrorType

Error type classification for OnError events

HookAction

Hook response action from SDK

HookEvent

Unified hook event enum

HookEventType

Hook event types

HookResult

Hook execution result

Traits

HookExecutor

Hook executor trait

HookHandler

Hook handler trait