Function build_entity_index 

pub fn build_entity_index<T>(content: &T) -> EntityIndex
where
    T: AsRef<[u8]> + ?Sized,

Build an entity index from content.

This intentionally shares EntityScanner’s HEADER skipping, quoted-string semantics, and its #3395 refusal of instance names wider than u32 (reported here, not handed back as a quietly short index), so scan and lookup agree.