The demand_index DB column comment still said "насыщающее преобразование"
(saturating) after #1167 switched it to city-relative normalization —
exactly the misleading-comment class that hid the original bug. Migration
147 updates COMMENT ON COLUMN (idempotent, comment-only, no data DDL).
Refs #948
demand_index used a fixed clamp01(velocity/50); on a live prod refresh
all 8 ЕКБ districts sold ≥50/mo so it saturated to 1.0 everywhere — zero
discrimination between districts. Redesign to mirror infra_index:
normalize each district's unit_velocity against the city reference (MAX
district velocity per refresh run), so demand always discriminates and
self-calibrates as the market grows (no magic constant to rot).
- normalize_demand(velocity, *, city_reference_velocity), pure + graceful
(None stays None; reference<=0 -> honest 0.0, no ZeroDivisionError)
- refresh_locations now two-pass: collect velocities (one
compute_market_metrics per district, no O(n^2)), derive city reference,
normalize + upsert; SAVEPOINT-per-row and counters preserved
- remove _DEMAND_SATURATION_UPM constant; log city_reference_velocity
- tests: rewrite demand normalization + add end-to-end city-relative
suite incl. discrimination regression guarding the all-1.0 prod bug
Refs #948
