Function scan_file 

pub fn scan_file(
    analyzer: &CppGraphSource<'_>,
    visibility: &VisibilityIndex<'_>,
    file: &ProjectFile,
    input: &FileEdgeScanInput<'_>,
) -> PerFileEdges

The C++ half of one file’s inverted pass: seed the scan context from the already-parsed tree and walk it, recording every caller -> callee edge the file names.

The pass’s fan-out – build_edge_output plus parse_and_collect, the shared language-agnostic driver – stays in brokk-bifrost-analysis and calls this once per kept file.