Background task output files in /private/tmp grow unbounded, no cleanup

Summary

Claude Code stores background task output in /private/tmp/claude-{UID}/ with no size limits, no TTL, and no automatic cleanup. A single runaway task output file consumed 405 GB of disk space, filling the drive to 99% capacity (236 MB free on a 926 GB disk).

Reproduction

1. Use Claude Code over many sessions (background tasks via run_in_background parameter)
2. Check /private/tmp/claude-{UID}/ — old session directories and task output files accumulate indefinitely
3. One pathological task output file (bzkdoq3qh.output) grew to 405 GB, likely from a command that produced massive stdout

Expected behaviour

• Task output files should have a size cap (e.g. truncate after 100 MB)
• Old session directories in /private/tmp/claude-* should be cleaned up on session start or after a TTL (e.g. 7 days)
• Users should be warned if a background task's output is growing beyond a reasonable threshold

Actual behaviour

• No size limit on task output files
• No automatic cleanup of old session temp directories
• No visibility to the user — the directory is hidden in /private/tmp and doesn't show up in normal disk usage tools like Finder or du -sh ~
• macOS doesn't reliably clean /private/tmp on reboot for large files

Impact

Severe — silently fills disk to capacity. The user had no idea where 405 GB went. The path /private/tmp/claude-501/ is not something anyone would think to check.

Environment

• macOS 15 (Darwin 25.2.0)
• Apple Silicon (M4)
• Claude Code (latest as of 2026-04-02)

🤖 Generated with Claude Code