Function environment 

pub fn environment(
    entity: &EntityState,
    action: Option<&str>,
) -> Vec<(String, Option<String>)>

entity’s environment contract: the set-or-unset pairs a Launcher or an Action step’s child receives. Some sets a variable, None unsets it, so an absent name can never be misread as one set to the empty string.

Covers exactly the eight REPON_ variables and all fifteen of git’s local environment variables (docs/spec/config.md), plus GIT_TERMINAL_PROMPT, force-set on every call regardless of shape or action. action names the running Action; None is REPON_ACTION’s own unset case, for a Launcher.

Destructures entity exhaustively so a Cell added to EntityState later fails to compile here rather than silently never reaching the environment.