Function plan_zone_with 

pub fn plan_zone_with(
    ctx: &GateCtx,
    named: Option<Utf8PathBuf>,
) -> PlanZoneTarget

The resolution, with the variable’s value supplied.

The environment is read at one boundary and passed in, so every case is reachable from a test. This crate forbids unsafe code, and setting a variable is unsafe from the 2024 edition on.