[DOCS] Missing `SubagentStart` input schema definition in Hooks reference

Documentation Type

Missing documentation (feature not documented)

Documentation Location

https://code.claude.com/docs/en/hooks

Section/Topic

The "Hook Input" section in the Hooks reference documentation.

Current Documentation

The "Hook Input" section currently lists schemas for:

• PreToolUse Input
• PostToolUse Input
• Notification Input
• UserPromptSubmit Input
• Stop and SubagentStop Input
• PreCompact Input
• Setup Input
• SessionStart Input
• SessionEnd Input

It jumps from PreCompact to Setup (or Stop/SubagentStop) without defining the input for SubagentStart.

What's Wrong or Missing?

Although SubagentStart is a valid lifecycle event (referenced in the "Plugins reference" documentation under Available events), there is no documentation in the primary Hooks reference regarding what data is passed to this hook via stdin.

Developers wishing to utilize the SubagentStart hook (e.g., to initialize resources when a subagent begins) have no reference for the JSON payload structure, available fields, or context provided.

Suggested Improvement

Add a new subsection under "Hook Input" specifically for SubagentStart Input.

It should likely resemble the SubagentStop input but tailored for the start event. Example placeholder structure (needs verification by engineering):

### SubagentStart Input

{
  "session_id": "abc123",
  "transcript_path": "~/.claude/projects/.../00893aaf-19fa-41d2-8238-13269b9b3ca0.jsonl",
  "permission_mode": "default",
  "hook_event_name": "SubagentStart",
  "subagent_name": "target_agent_name" // If applicable
}

Impact

High - Prevents users from using a feature

Additional Context

• This event was reportedly added in recent versions (Changelog 2.0.43 mentions the addition of the SubagentStart hook event).
• The event is listed as valid in docs/en/plugins-reference but is missing the implementation details in docs/en/hooks.