Function write_home_config 

pub(crate) fn write_home_config(
    api: &str,
    channel: &str,
    key_file: &str,
) -> Option<String>

Records the node, channel and key in ~/.choir/config.

The fallback the .choir/config walk reaches when no directory above the working one names a node — see configured. Existing keys are preserved rather than the file being rewritten, because choir init writes this same file when it is run from $HOME.

None when it could not be written, which is reported rather than fatal for the same reason configure_git_credential’s failure is.