one move: measure behavior
Build the first vector index as an exact inner-product scan that returns stable document IDs. In the Vector Search system, implement this level as a deterministic contract before composing it with the next service.
def top_k_similar(query, vectors, k): return [document_id, ...]
top_k_similar([1, 0], {'a': [1, 0], 'b': [0, 1], 'c': [0.5, 0]}, 2)
?
top_k_similar([0, 1], {'a': [1, 0], 'b': [0, 1]}, 1)