Function with_real_git 

pub fn with_real_git(
    variables: &[(OsString, OsString)],
    real_git: &Path,
) -> Vec<(OsString, OsString)>

What: variables with the forward-target variable added for real_git when the variables do not name one. Why: The wrapper process learns the system configuration path from the real Git named by that variable. The environment entry.rs builds always carries it, but a resident process (the service) and callers that hold only a Git path and a bare overlay do not, and without it every read there would decline; the caller knows the Git it runs.

In TS you’d write (pseudocode):

const named = { [FORWARD_TARGET]: realGit, ...variables }; // the variables win when they name one