`codex search paper` crashed on the live DB with "operator does not exist:
vector <-> double precision[]". The pgvector `<->` operator needs its RHS
typed as vector; peer call sites (mcp_server.py, wiki.py) cast but the CLI
did not. Mocked unit tests never exercise real pgvector, so it went unseen.
Add the cast to both `<->` occurrences and a regression guard asserting the
SQL contains `::vector`.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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