[BUG] Parent token counter increases while subagent (Task tool) is running

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)
• [x] I am using the latest version of Claude Code

What's Wrong?

While a subagent (Task tool) is running, the parent session's token counter (bottom-left of TUI) gradually increases, even though the parent should be idle waiting for the subagent to complete.

Observed behavior:

Parent session's status line (bottom-left) during subagent execution:

✶ Wrangling… (18s · ↓ 391 tokens · thought for 3s)
· Wrangling… (41s · ↓ 451 tokens · thought for 3s)
✻ Wrangling… (1m 18s · ↓ 508 tokens · thought for 3s)
· Wrangling… (2m 20s · ↓ 933 tokens · thought for 3s)
✽ Wrangling… (3m 37s · ↓ 2.4k tokens · thought for 3s)

Subagent completion message:

Done (24 tool uses · 29.8k tokens · 3m 21s)

Key observations:

• Parent token counter: 391 → 2.4k (+2k) over ~3.5 minutes while subagent ran
• Subagent consumed 29.8k tokens total
• The increase is gradual (not a single jump), suggesting periodic consumption
• "thought for 3s" remains constant → parent's thinking is not being updated
• promptSuggestionEnabled: false was confirmed, so prompt suggestions are not the cause

What Should Happen?

While a subagent is running, the parent's token counter should remain stable since no API calls should occur for the idle parent session.

Error Messages/Logs

No error messages. Discovered by observing the TUI token counter during subagent execution.

Steps to Reproduce

1. Start a session with extended thinking (Opus)
2. Note the current token count in the bottom-left status line
3. Invoke Task tool with a subagent that takes several minutes (e.g., subagent_type: "general-purpose")
4. Watch the bottom-left token counter while the subagent runs
5. Observe it gradually increasing despite the parent being idle

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.25

Platform

Anthropic API

Operating System

Ubuntu/Debian Linux

Terminal/Shell

VS Code integrated terminal

Additional Information

Related issues (not duplicates):

• #13977: Statusline tokens are cumulative and don't reset on /clear (related: both about cumulative counting, but this issue is about consumption during idle state)
• #15704: Subagent token counter shows different metrics during vs after execution (related: token counting, but about subagent's own counter, not parent's)

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✍️ Author: Claude Code (Dev Container) with @carrotRakko

Note: This issue was written and submitted by an AI agent (Claude Code), with human review and approval.