M8-T05: bind electricity costs to source bindings

app/models/energy.py

@@ -13,7 +13,17 @@ from __future__ import annotations
 
 import uuid as _uuid
 from datetime import datetime
-from sqlalchemy import Boolean, DateTime, Float, ForeignKey, Integer, String, UniqueConstraint, event, text
+from sqlalchemy import (
+    Boolean,
+    DateTime,
+    Float,
+    ForeignKey,
+    Integer,
+    String,
+    UniqueConstraint,
+    event,
+    text,
+)
 from sqlalchemy.orm import Mapped, mapped_column, relationship, synonym
 from sqlalchemy.types import JSON
 
@@ -53,9 +63,7 @@ class Meter(Base):
     id: Mapped[int] = mapped_column(Integer, primary_key=True, autoincrement=True)
 
     # Stable internal identity — used as HA Discovery unique_id anchor.
-    uuid: Mapped[str] = mapped_column(
-        String(36), unique=True, nullable=False, default=_uuid4_str
-    )
+    uuid: Mapped[str] = mapped_column(String(36), unique=True, nullable=False, default=_uuid4_str)
 
     # Human-readable label for this physical meter (e.g. address, serial, tariff zone).
     label: Mapped[str] = mapped_column(String(255), nullable=False)
@@ -207,15 +215,11 @@ class EnergyContractVersion(Base):
     )
 
     # Start of this version's validity window (inclusive, UTC).
-    effective_from: Mapped[datetime] = mapped_column(
-        DateTime(timezone=True), nullable=False
-    )
+    effective_from: Mapped[datetime] = mapped_column(DateTime(timezone=True), nullable=False)
 
     # End of this version's validity window (exclusive, UTC).  NULL means open-ended
     # (i.e. this is the most recent / current version).
-    effective_to: Mapped[datetime | None] = mapped_column(
-        DateTime(timezone=True), nullable=True
-    )
+    effective_to: Mapped[datetime | None] = mapped_column(DateTime(timezone=True), nullable=True)
 
     # Pricing values as a JSON object conforming to the profile structure for
     # ``contract.kind`` (validated by the application layer against the YAML profile).
@@ -320,8 +324,8 @@ class EnergyCostPeriod(Base):
         ForeignKey("meter.id", ondelete="RESTRICT"), nullable=True
     )
 
-    # Nullable while M8 adopts historical DSMR rows.  Future normal periods
-    # will point at the binding that supplied both cumulative endpoints.
+    # Nullable for historical and degraded rows.  Every new normal period
+    # points at the one binding that supplied both cumulative endpoints.
     source_binding_id: Mapped[int | None] = mapped_column(
         ForeignKey("meter_source_binding.id", ondelete="RESTRICT"), nullable=True
     )