Table of contents The good news first The symptom My Zsh history config Tracing the behavior inotify fatrace strace bpftrace Making it crash! What was the bug? Conclusion Appendix A: Bonus Footgun: exported HISTFILE Appendix B: Bonus Question: Can AI find this bug? Eval setup: symptom + bpftrace Eval variant: habit-hinted AI Conclusion For many years, I sometimes discovered that commands I was sure I had run were no longer present in my Z shell history file ( ~/.zsh_history ). In this article, I will show you how I tracked down the bug. Spoiler: ultimately, patching Zsh to make it crash loudly and analyzing the crash’s core dump was the winning strategy! The good news first Zsh 5.9.2 (released July 12th, 2026) contains a fix for this issue — open it after reading this investigation to not spoil the fun.…