I use zsh per directory history [0] as well as this cron job I have set to run hourly:

    #!/bin/bash

    cd /Users/nmjohn/.directory_history \
      && git add . \
      && git commit -m "Automatic Backup: `date`" \
      && echo "Files Modified:" \
      && git log head -1 --name-only --pretty=format:"" | grep "[^\s]" | awk '{print    "\t\t"$0}' \
      && echo ""

It's not bullet-proof, but since I never manually touch the directory it's worked without hiccup for the last ~6 months. When trying to remember the syntax to a rarely used function (or even the name itself) or coming up with a gnarly awk/sed/grep command, it's been incredibly helpful to have fairly granular search capability to go back and find them weeks later.

Also ctrl+g in a terminal toggles between per directory history and global history which makes context switching easier when switching to a project not touched for a while.

[0]: https://github.com/jimhester/per-directory-history