[BUG] When using subagents in parallel event log trace Is useless

Environment

• Platform (select one):
• [ X] Anthropic API
• [ ] AWS Bedrock
• [ ] Google Vertex AI
• [ ] Other: <!-- specify -->
• Claude CLI version: <!-- output of claude --version -->
• Operating System: macOS 14.3
• Terminal: All

Bug Description

As shown in this trace 3 subagents are started, but on subagentstop it's impossible to determine what subagent stopped? SubagentStop should hold subagent name but does not.

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{"session_id": "681d943d-ce16-41f1-874c-2b1731fa3699", "transcript_path": "/Users/nmrcontinia.com/.claude/projects/-Users-nmrcontinia-com-Documents-git-claude-code-hooks/681d943d-ce16-41f1-874c-2b1731fa3699.jsonl", "cwd": "/Users/nmrcontinia.com/Documents/git/claude-code-hooks", "hook_event_name": "UserPromptSubmit", "prompt": "use task paralization to use story writer to write 3 stories in parallel"}
{"session_id": "681d943d-ce16-41f1-874c-2b1731fa3699", "transcript_path": "/Users/nmrcontinia.com/.claude/projects/-Users-nmrcontinia-com-Documents-git-claude-code-hooks/681d943d-ce16-41f1-874c-2b1731fa3699.jsonl", "cwd": "/Users/nmrcontinia.com/Documents/git/claude-code-hooks", "hook_event_name": "PreToolUse", "tool_name": "Task", "tool_input": {"description": "Robot learns painting", "prompt": "Write a heartwarming story about a robot named Circuit who discovers the joy of painting. The robot starts out only understanding binary and logic, but through an accidental encounter with spilled paint in a factory, discovers color and creativity. Make it touching and about 3-4 paragraphs long.", "subagent_type": "story-writer"}}
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Steps to Reproduce

I created simple story writer subagent and then asked Claude following request:
Use task paralization to use story writer to write 3 stories in parallel

Expected Behavior

Should be able to track what subagent stopped

Actual Behavior

Gets stop event with no subagent name:
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Additional Context

This missing feature makes it impossible to make advanced control flow using Claude Code