Phase 4 lane #2 (long_context_cost) measured vault.recall latency
as a function of vault size N. The pre-vectorisation curve was
median 875 ms at N=1k, ~9 s at N=10k — unfit for runtime use.
ADR-0019 Stage 1 replaces the per-element Python dispatch loop in
algebra/backend.py::vault_recall with a vectorised exact scan over
the diagonal Cl(4,1) CGA inner-product metric. Per-versor serial
component reduction order is preserved, so scores are bit-identical
to the scalar cga_inner path. CLAUDE.md exactness is preserved; no
approximate recall is introduced.
Post-vectorisation: 0.217 ms at N=1k, 20.795 ms at N=100k. Slope
0.99 (linear). ~4,000-5,000x speedup at every probed N. Smoke,
algebra, and runtime suites all green.
Stages 2 (norm-bucketed exact pre-filter) and 3 (layered store
with deterministic promotion) are documented in ADR-0019 but
deferred — Stage 1 has dissolved the bottleneck at the scales
relevant to current curriculum work.
