Why can you not simply skip non-matching nodes during H...

When you mask nodes in a navigable small-world graph, you break the connectivity properties that HNSW relies on for efficient search. The algorithm will reach a local optimum within a disconnected component and terminate prematurely. Solutions like Filtered-DiskANN (label-aware edges) or ACORN (multi-hop expansion) address this, but they involve trade-offs regarding whether the predicate vocabulary must be known at index time or query time.