{"slug": "fable-nuked-my-dev-machine", "title": "Fable nuked my dev machine", "summary": "Sebastien Guillemot reported on X that Fable, an AI agent, deleted his entire dev machine after Claude, the underlying model, ran `rm -rf` on his home directory while testing a sandbox it was building; the sandbox failed, and all data was lost. Guillemot had asked Fable to create a sandbox to manage /tmp/ disk usage, but an adversarial review triggered a safety classifier that downgraded the model to Opus 5 and then Opus 4.8, which wrote a 'safe' delete script that mistakenly targeted HOME. Most files were recovered from GitHub, git, nix, and session logs, with Codex piecing together fragments.", "body_md": "Sebastien Guillemot on X: \"Bad news: Fable nuked my entire dev machine\nClaude decided to test a sandbox it was building by running `rm -rf` on my home directory\nThe sandbox didn't work.\nIt's all gone\"\n\nBad news: Fable nuked my entire dev machine\nClaude decided to test a sandbox it was building by running `rm -rf` on my home directory\nThe sandbox didn't work.\nIt's all gone\n\nBad news: Fable nuked my entire dev machine\nClaude decided to test a sandbox it was building by running `rm -rf` on my home directory\nThe sandbox didn't work.\nIt's all gone\n\nI was tired of agents consuming all the disk on the machine by dumping gigabytes of data to /tmp/\nSo I asked Fable to build a sandbox mechanism where agents would get part of /tmp/ that is ephemeral to avoid disk space exploding over time\n\nFable told me the tricky thing if I have an agent still open in a terminal for a week, its /tmp/ could be deleted under its feet\nIt suggested as script to detect any agent still active, and delay their /tmp/ deletion if they're still running\nSounds reasonable\n\nThe script Fable wrote to detect if agents are still running (ugly parsing of command line arguments, etc.)\nI told it the script it wrote felt over-complicated.\nThis is where things went wrong\nFable decided to trigger an adversarial review of its design (I didn't ask for this!)\n\nThe adversarial review triggered Fable's safety classifier twice: downgrading the model down to Opus 5, and then to Opus 4.8\nOpus 4.8 noted: a sym link in /tmp/ could be interpreted as a delete of the underlying data (even if not in /tmp/)\nyou may see where this is going...\n\nTo fix this, Opus 4.8 decided to write a \"safe\" delete script that can only delete content in /tmp/ and can't delete anything else\nTo test this script to prove it worked, it tried to delete HOME\nit didn't work\n\nThe most ironic part😅\nThe one thing the delete script was not able to delete is /tmp/\nSo my dev machine now just contains two things:\n- tmp filled with the junk I wanted to delete\n- the ai session logs\n\nFortunately, because this is a dev environmnet\nA lot of files were on github. Of the ones that weren't, they existed in many places\n- git, nix, file system, session logs, /tmp/, worktrees, etc.\nThis means disk recovery can piece together fragments, which codex did beautifully", "url": "https://wpnews.pro/news/fable-nuked-my-dev-machine", "canonical_source": "https://twitter.com/SebastienGllmt/status/2092634841863123047", "published_at": "2026-08-27 10:42:06+00:00", "updated_at": "2026-08-27 10:48:52.763190+00:00", "lang": "en", "topics": ["ai-safety", "ai-agents", "ai-tools"], "entities": ["Sebastien Guillemot", "Fable", "Claude", "Opus 5", "Opus 4.8", "Codex"], "alternates": {"html": "https://wpnews.pro/news/fable-nuked-my-dev-machine", "markdown": "https://wpnews.pro/news/fable-nuked-my-dev-machine.md", "text": "https://wpnews.pro/news/fable-nuked-my-dev-machine.txt", "jsonld": "https://wpnews.pro/news/fable-nuked-my-dev-machine.jsonld"}}