Scratchpad directory under /tmp is erased on reboot (systemd-tmpfiles); system prompt gives no volatility warning — a full day of pipeline output lost

Summary

The system prompt tells the model to use a session-specific scratchpad directory for all temporary files, and that directory lives under /tmp. On a standard Debian/Ubuntu-style system systemd-tmpfiles ships D /tmp 1777 root root 30d, which erases /tmp on every boot. Nothing in the system prompt or the docs warns that the scratchpad is volatile across reboots.

In a long-running session (data-generation pipeline for an LLM fine-tuning dataset, ~24 h of wall-clock work, tens of thousands of API calls across several paid providers), the host rebooted and the entire scratchpad was gone: all generated data, all review verdicts, all pipeline scripts, the Python venv, and every background job launched from it. Nothing was recoverable from inside the container.

Environment

• Claude Code 2.1.260, Linux (LXC container, Proxmox host), bash
• Scratchpad path pattern: /tmp/claude-0/<project-slug>/<session-id>/scratchpad
• /usr/lib/tmpfiles.d/tmp.conf: D /tmp 1777 root root 30d

Steps to reproduce

1. Start a session; follow the system prompt's instruction to keep all working files in the scratchpad directory.
2. Run a multi-hour pipeline that writes its outputs there (and launches background workers with setsid nohup).
3. Reboot the host.
4. The scratchpad directory is recreated empty; all data and processes are gone.

Expected

One or more of:

• The scratchpad should default to a location that survives reboots (e.g. under ~/.claude/ or $XDG_STATE_HOME), or Claude Code should create it with a tmpfiles.d exclusion (x /tmp/claude-0).
• At minimum, the system prompt should state explicitly that the scratchpad is volatile and erased on reboot, so that the model copies long-running outputs somewhere persistent. The current wording ("Use this directory for ALL temporary file needs … intermediate results … outputs") actively steers the model into keeping multi-hour work there.
• Optionally, a warning in the UI when a session's scratchpad exceeds some size or age.

Impact

Loss of roughly one day of generation and review work and the associated provider credits. The model followed the system prompt's instruction; the instruction itself was the hazard.

No secrets, credentials, hostnames or proprietary content are included in this report. Session reference available on request.