Function sibling_path 

pub(crate) fn sibling_path(
    base: &OsStr,
    output: &Path,
    meta: &PlatformMeta,
    ext: &str,
) -> PathBuf

Build a sibling path of output named <base>-<isolation><ext>, where base is output’s stem, <isolation> is derived from meta.platform, and ext includes the leading dot (e.g. ".json" or ".cbor").