"hooks": {
    "PreToolUse": [
      {
        "matcher": "Edit|Write",
        "hooks": [
          {
            "type": "command",
            "command": "if command -v jj >/dev/null && jj root >/dev/null 2>&1; then if ! jj status >/dev/null 2>&1; then echo 'WARNING: failed to snapshot jj repository, tell user to fix'; fi; fi"
          }
        ]
      }
    ],
    "PostToolUse": [
      {
        "matcher": "Edit|Write",
        "hooks": [
          {
            "type": "command",
            "command": "if command -v jj >/dev/null && jj root >/dev/null 2>&1; then if ! jj status >/dev/null 2>&1; then echo 'WARNING: failed to snapshot jj repository, tell user to fix'; fi; fi"
          }
        ]
      },

In newer jj there’s a dedicated snapshot command but I’ve not updated yet. Pop this in your Claude Code settings.json. It will snapshot the repository, thus recording any changes. Explore with jj evolog.

In .claude/settings.json you can trigger shell commands on events like SessionStart, Stop, PreCompact, and PostToolUse [1].

I have all of them run `jj status`, because jj snapshots the working copy every time it's invoked.

You can have Claude write the hooks, but mine is:

`[[ -d .jj ]] && jj status >/dev/null 2>&1; exit 0`

[1] https://code.claude.com/docs/en/agent-sdk/hooks

The others use `jj status`, but if I were to do this, I'd use `jj log -n0`, which has no output. All you really need is any read-only jj command.

You could also turn on watchman and have this property on every save of a file and not even need to worry about hooks.