I created a private repository within `registries/customer-projects`.
This holds flakes.
The folder is registered as registry.
That allows to run the following from within a customer project:
nix run cp\#reuter-phpstan
In order to execute the customer specific application from flake.
The phps used via flake for local development of legacy projects
distributed pre build packages via cachix.
Install cachix and add configuration to allow fetching of pre compiled
packages.