> `ctx.Value` is an `any -> any` kv store that does not come with any documentation, type checking for which key and value should be available

The docs https://pkg.go.dev/context#Context suggest a way to make it type-safe (use an unexported key type and provide getter/setter). Seems fine to me.

> What if you just use a custom struct with all the fields you may need to be defined inside?

Can't seamlessly cross module boundaries.