DEVENV_ROOT is incorrect if project moves

[therealpxc]

Describe the bug
When a project moves, its .direnv cache still exists and has cached the old DEVENV_ROOT value. This breaks scripts that refer to DEVENV_ROOT (for instance Poetry activation in the Python language module).

To reproduce
Create a devenv project, activate direnv with direnv allow and cd into it. Then rename the project directory to something else, leave the directory and return to it. Run direnv allow and then echo $DEVENV_ROOT.

Version

devenv 1.1.0 (aarch64-darwin)

Workaround
Problem goes away if you nuke .direnv.

[therealpxc]

Maybe we can fix this by adding a file under .devenv whose contents are the last value of DEVENV_ROOT, and add it to our direnv watched files? I'd be happy to implement that if that solution is agreeable.