cache not invalidated in --impure mode if a watched file changes

Hello, I have a few projects where I cannot add flake files, and they are also using `mise` as tool. I've built [`mise2nix`](https://gitlab.com/nolith/mise2nix) and when I cannot have the flake files checked it, I keep [a global flake](https://gitlab.com/nolith/mise2nix/-/blob/main/templates/mainflake/flake.nix) on my workstation and then set every projects with `echo "use flake ~/src/mainflake --impure" >> .envrc`. The problem is that if `.tool-versions` files changes, direnv still loads the environment from it's cache but it will be incorrect because the `buildInputs` is generated from the content of `.tool-versions`. I was hoping that adding `watch_file .tool-versions` could be enough, but it only reloads the flake from the cache. Is there a way I can set extra files that should invalidate the cache?