Replaces the rank-interleaved fusion with a straight merge of the union
sorted by each candidate's raw retrieval score, ties still falling to
declaration order, cut at limit. This is the depth-quota candidate: within
one database rank order and raw-score order coincide, so the whole
difference from the tie-break fix is the cross-database interleaving.
This branch exists to be measured and discarded. The rank-dominance tests
in tests/multi_db/test_search.py pin the behaviour this deliberately
inverts, so the root suite FAILS here by design. If the arm wins, the
shipping implementation belongs to the session that owns client/search.py,
with its own tests.
Claude-Session: https://claude.ai/code/session_01WhudUtZm6qqiuv8Y1sbwSc
a19f2c96b1