[BUG] Background bash command output has no size limit — can fill disk

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?

When using the Bash tool with run_in_background: true, output is captured to a file under /private/tmp/claude-*/tasks/<id>.output. This file has no size limit, so a single runaway command can fill the
entire disk.

A background bash command (tail following a symlink to an active agent's JSONL output) created a 297 GB output file.

What Should Happen?

Background command output files should have a reasonable size cap (e.g. 100 MB), after which output is truncated or the command is killed.

Error Messages/Logs

Steps to Reproduce

1. Launch 3 background agents with run_in_background: true
2. Before they complete, run a background bash command that reads their output files:

for f in /private/tmp/claude-/tasks/.output; do
tail -5 "$f"
done

1. The .output files are symlinks to agent JSONL files that are actively being written to
2. The bash command's own output capture file (bspzktftx.output) grows unboundedly as tail follows the symlinks
3. Result: a single 297 GB file in /private/tmp/claude-*/tasks/

The core issue is that tail on a symlink to a growing file produces continuous output, and there's no size cap on the background command's output capture. But even without the symlink detail, any background
bash command that produces large output would hit the same problem.

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.76 (Claude Code)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

IntelliJ IDEA terminal

Additional Information

_No response_