Module process_env 

Process environment with a thread-local overlay for tests.

Production reads std::env. Tests call override_var so they never need set_var / remove_var, which are unsafe in edition 2024.

Functions

clear_override

Drop the overlay for key so later reads use the real process environment.

override_var

Pretend key is value (None means unset) on this thread.

var

Read key, honouring a test overlay if one is set on this thread.