I heartily agree with #2 if the language isn't Zig. Which actually supports your point: allocating in leaf functions is idiomatic in Zig, and it works out fine, because there's no allocation without an Allocator, and even if that's passed in implicitly as part of a struct argument, error{OutOfMemory} will be part of the function signature. So there's no losing track of what allocates and what doesn't.

This actually supports your broader point about always passing state to functions, and never accessing it implicitly. Although I don't know that I agree with extending that to constants, but maybe with another several decades of experience under my belt I might come to.

Zig also makes it easy for 'constants' to change based on build-specific parameters, so a different value for testing, or providing an override value in the build script. I've found that to eliminate any problems I've had in the past with global constants. Sometimes, of course, it turns out you want those values to be runtime configurable, but as refactorings go that's a relatively straightforward one.

> Give these a try. I bet you'll like the results!

It sounds like too many words to refer ro plain old inversion of control and CQRS. They're both tried and true techniques.