[BUG] Ghost sessions created with unexpected stdin content on Windows when using subagents

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [ ] I am using the latest version of Claude Code

What's Wrong?

Multiple "ghost" sessions were created with C:/Program Files/Git/help as the first message, but I never typed this content. These sessions appeared in my resume list even though I didn't initiate them.

Key evidence:

4 independent sessions were created within a 2-hour window, all with identical first message C:/Program Files/Git/help:

| Session ID | Timestamp | File Size |
|------------|-----------|-----------|
| 12bd3669-b30d-4377-9a3b-d4d3d7857170 | 2026-05-09T07:01:28 | 6.6KB |
| 8a3ec0bf-9357-47ab-af7c-7b07f59ef857 | 2026-05-09T07:39:03 | 189KB |
| 79a0f413-e6ad-4162-ade8-a0980a162f99 | 2026-05-09T08:54:41 | 4.6KB |
| 228b9365-c7a5-4ae3-b989-5cb6ef7e61a1 | 2026-05-09T08:57:25 | 12.9KB |

What Should Happen?

Sessions should only be created when the user explicitly initiates them. No "ghost" sessions with unexpected content should appear.

Error Messages/Logs

Each problematic session's JSONL file shows:

{"type":"queue-operation","operation":"enqueue","timestamp":"2026-05-09T07:01:28.124Z","sessionId":"12bd3669-b30d-4377-9a3b-d4d3d7857170","content":"C:/Program Files/Git/help"}
{"type":"queue-operation","operation":"dequeue","timestamp":"2026-05-09T07:01:28.126Z","sessionId":"12bd3669-b30d-4377-9a3b-d4d3d7857170"}
{"parentUuid":null,"isSidechain":false,"type":"progress","data":{"type":"hook_progress","hookEvent":"SessionStart"...}
{"parentUuid":"...","isSidechain":false,"promptId":"...","type":"user","message":{"role":"user","content":"C:/Program Files/Git/help"}...}

Notable observations:

• The enqueue-dequeue interval is only 2ms - characteristic of programmatic input
• SessionStart hook log appears at 07:01:24.460Z, before the enqueue at 07:01:28.124Z - message was enqueued during session initialization, not before

Steps to Reproduce

Unfortunately, I cannot reliably reproduce this issue. The conditions when it occurred:

1. I was running a main session (64e42eba-41ff-45be-8c81-dc17f63850d7) with heavy subagent usage (multiple Agent tool invocations, some with run_in_background: true)
2. The ghost sessions appeared at different times during this session
3. I have the superpowers plugin (v5.1.0) installed
4. I was using Git Bash on Windows Terminal

Investigation findings:

• The ghost sessions are NOT child sessions of any Agent tool invocation (no parentSessionId linking)
• The C:/Program Files/Git/help path is NOT generated by any plugin hook code
• The sessions have userType: "external" and entrypoint: "cli" - appearing as normal CLI sessions
• The path C:/Program Files/Git/help doesn't exist as a valid directory

Claude Model

Other (using third-party API)

Is this a regression?

I don't know

Last Working Version

N/A

Claude Code Version

2.1.80 (Claude Code)

Platform

Other

Operating System

Windows

Terminal/Shell

Windows Terminal

Additional Information

Root cause analysis:

Key structural difference compared to normal sessions:

| Session Type | First Record in JSONL | Key Difference |
|--------------|----------------------|----------------|
| Normal session | SessionStart hook | User message processed directly, no queue-operation |
| Ghost session | queue-operation enqueue | Message was queued first (abnormal) |

This is the core anomaly: Normal sessions do NOT have queue-operation at the start. Something injected content into the queue before the session was ready.

The root cause is unknown. Based on the evidence, we can confirm:

• When: Content was injected into the queue during session startup
• What: The injected content was C:/Program Files/Git/help
• How fast: 2ms enqueue-dequeue interval indicates programmatic input
• Unknown: What process/component triggered this injection

Possible areas to investigate:

• stdin capture during session initialization
• Windows Terminal buffer behavior

Context when issue occurred:

• Heavy subagent usage (multiple Agent tool invocations)
• Windows Terminal with Git Bash
• superpowers plugin v5.1.0 installed

Why this is likely a bug:

• The path C:/Program Files/Git/help is not valid (actual Git help is in mingw64/share/git-core-doc)
• No plugin code generates this path
• Queue-operation at session start is abnormal (normal sessions don't have this)