Where does pre-commit install “environments”?

The environments are installed into a cache:

pre-commit by default places its repository store in ~/.cache/pre-commit — this can be configured in two ways:

• PRE_COMMIT_HOME: if set, pre-commit will use that location instead.
• XDG_CACHE_HOME: if set, pre-commit will use $XDG_CACHE_HOME/pre-commit following the XDG Base Directory Specification.

disclaimer: I am the author