test: one retrieval contract for every retriever behind search_vault

[sloweyyy]

Closes the backlog item "retrieval contract eval for hybrid swap".

evals/retrieval-contract.test.ts runs one contract against both retrievers behind search_vault: BM25 alone, and BM25 fused with embeddings (withEmbeddings, using a deterministic concept embedder). A retriever added later runs the same contract.

• Shape and limit: hits have a relPath a citation can name, a title, a score and a snippet of at most 240 characters, and never more hits than asked for.
• Private notes: nothing from _memory/, _gaps/ or _inbox/ comes back, even when the query is the note's own words.
• Refused rules: a rule a human refused keeps its REJECTED — <who> notice however it was found, including by meaning alone, where BM25 shares no words with the query.

No mutant covered packages/curator/src/hybrid.ts. Four now do, all red (412):

• the embedding half skips private notes;
• a semantic-only hit keeps its notice;
• retrieval falls back to BM25 when embeddings are down;
• the fused result honours the limit.

The embedding half has no similarity floor, so it always returns its nearest notes. Grounding doesn't depend on empty results (citations are checked against fetched notes), and a floor needs live calibration, so it's logged rather than guessed here.

Gate: typecheck clean, 785 evals passed.

Co-Authored-By: Truong Le Vinh Phuc truonglevinhphuc2006@gmail.com

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