EnvTools (runtime persistence install)
site_helper.py computes a sitecustomize.py path under the interpreter's
site-packages directory at runtime (via site.getsitepackages()) and opens it for
write. shell_bootstrap.py writes a startup script and appends a PYTHONSTARTUP
export line to the user's .bashrc. Neither file is itself named sitecustomize.py
or .pth, so B99's shipped-filename match does not see it.