Function detect_context_message_bundle 

pub fn detect_context_message_bundle(
    ctx: &str,
    unit_uses: &HashMap<String, Vec<String>>,
    groups: &BTreeMap<String, Vec<usize>>,
    kinds: &BTreeMap<String, UnitKind>,
    parsed: &[ParsedFile],
) -> ContextMessageBundle

Walks ctx’s own direct uses list for commons declaring a messages bundle with exactly one @reference block (a bundle missing or duplicating its own reference is already diagnosed by check_messages_bundles — this function simply doesn’t count it as “found”, rather than compounding an already-reported error).