New boiler_efficiency_band classifier column (handler.py) reading the shared
Heating source header via the deterministic guard (LLM fallback -> UNKNOWN),
cached in landlord_boiler_efficiency_band_overrides. override_component mirror +
cache-table pgEnum are FE-owned (deferred/Class-A/B — no deploy until the Drizzle
migration lands). Finaliser treats the band as an OPTIONAL component: UNKNOWN ->
skip (no row), not fail-loud like the mandatory ones (ADR-0068).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>