Function remote_env 

pub fn remote_env(
    ssh: Ssh,
) -> (Vec<&'static str>, Vec<(&'static str, &'static str)>)

The configuration and environment every call that talks to a REMOTE for a verifier runs with, as data so both branches are testable without touching the process environment.

Never a prompt: GIT_TERMINAL_PROMPT=0 alone is not enough, because git runs GIT_ASKPASS / core.askPass / SSH_ASKPASS BEFORE consulting it; a GIT_ASKPASS that is present and EMPTY makes git run none of them. GCM_INTERACTIVE and credential.interactive tell credential managers the same; the helpers themselves stay, so stored credentials still work. Never a stall: curl gives up after 10 s under 1 byte/s, ssh after a 10 s connect — and the caller’s own deadline covers the rest.