Does Zig offer (guaranteed) tail call optimisation?

> Where recursion is useful, [...]

Recursion is so useful, most imperative languages even have special syntax constructs very specific special cases of recursion they call 'loops'.

> Does Zig offer (guaranteed) tail call optimisation?

Yes[1]. You can use the @call builtin with the .always_tail modifier.

    @call(.always_tail, foo, { arg1, arg2, ... });