Function resolve_angle_bracket 

pub fn resolve_angle_bracket(
    include_path: &str,
    importing_file: &str,
    file_index: &FileIndex,
) -> Option<String>

Resolve an angle-bracket include path against the file index.

Called from build_edges for C++ files whose #include <path> was classified as External at parse time. If the path resolves to a known repo file it is actually internal — the edge builder will create an Imports edge instead of skipping.