Function compile 

pub fn compile(
    file: FileId,
    name: &str,
    src: &str,
    diags: &mut Diagnostics,
) -> Option<Placed>

The whole front end: parse, expand, check, place, split.

One function, so beck check, beck run, beck build and the test harnesses cannot drift apart — §4.6’s “one binary serves beck build, beck check, beck lsp and beck explain; there is no separate language server implementation to drift.”