The mind decides membership (Mind::members) before the index is asked; the
index scores exactly the members (Qdrant has_id + exact) and the page carries
one cosine score per row. Deletes OVERSAMPLE_MAX, the x4 oversample, the
unfiltered VectorIndex::search contract and check_semantic.
Not yet compiled when committed: the first Yggdrasil run follows.
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
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