Module scan 

Flat scans — the passes that read the tree as a directory, not as a graph.

Three of the four things resolution needs cannot themselves be found by following links, because they are what makes following links possible. The TitleIndex is the clearest case: nominal references ([[My File]]) resolve through it, and a nominal reference may itself be spanning (contents: alias), so building the index by walking the tree would need the index to walk the tree. It is a flat filesystem scan for exactly that reason — a derived cache (DESIGN §5), rebuilt on demand and never persisted.

scan_ids and content_documents are the same shape: enumerate what is on disk, decide nothing about it. direct_child_files is the bounded variant the census uses — the directories the graph already reaches, and no others, so a vendored subtree or a nested workspace is never swept in (DESIGN §8).