Deterministic 3-layer склад предложения (ТЗ §9.3), read-only compute returning
SupplyLayerRow dataclasses for the #950 Step5 worker to UPSERT into supply_layers
(m.125). Mirrors market_metrics.py house style (frozen dataclass, _SQL consts,
graceful-to-empty, pure helpers, CAST(:x AS type)).
- L1 open: objective_lots available lots per district x class (objective/high)
- L2 hidden: SUM max(0, flat_count - free_flats) per district, mapping-free via
domrf_kn_objects (free_flats m.124) - no domrf<->objective join (domrf_declared,
medium/low by free_flats coverage). NULL free_flats excluded (no sold column).
- L3 future: domrf multiphase (ready_dt beyond 12mo horizon, ~no listed flats)
grouped by dev_group_name (domrf_multiphase/low). graddoc_stub deferred to #956.
Latest-snapshot DISTINCT ON guards against cross-snapshot double-count
(domrf_kn_objects is UNIQUE(obj_id, snapshot_date)). Only whitelisted
source/confidence values (m.125 CHECK). 45 unit tests, ruff clean.
