ThothII/docs/adr/0007-add-bm25-without-rebuilding-qdrant.md

Add BM25 without rebuilding the shared Qdrant collection

The workspace keeps its existing unnamed dense vector and adds only the sparse bm25 vector with IDF through Qdrant's additive vector-schema operation. Only Evidence points are repopulated with both default dense and BM25 values. Schema, Memory and solved questions retain their current dense points and are verified before and after the upgrade.

This replaces the planned destructive conversion to a named dense vector. If BM25 is missing, Evidence preprocessing may add it and verify the resulting schema; session runtime remains read-only. An incompatible existing BM25 definition fails without mutation. A candidate failure leaves the additive schema in place while Evidence stays unavailable, avoiding data loss in the other workflow modules.