M34: enforce domain integrity in PostgreSQL

backend/app/models/booking.py

@@ -1,7 +1,7 @@
 import uuid
 from datetime import datetime
 
-from sqlalchemy import Boolean, DateTime, ForeignKey, Integer, String
+from sqlalchemy import Boolean, CheckConstraint, DateTime, ForeignKey, Index, Integer, String
 from sqlalchemy.dialects.postgresql import UUID
 from sqlalchemy.orm import Mapped, mapped_column
 
@@ -13,6 +13,22 @@ BOOKING_STATUSES = ("reserved", "active", "returned", "cancelled", "blocked")
 
 class Booking(UUIDPrimaryKeyMixin, TimestampMixin, Base):
     __tablename__ = "bookings"
+    __table_args__ = (
+        CheckConstraint(
+            "status IN ('reserved','active','returned','cancelled','blocked')",
+            name="ck_bookings_status",
+        ),
+        CheckConstraint("ends_at > starts_at", name="ck_bookings_time_window"),
+        CheckConstraint(
+            "start_odometer_km IS NULL OR start_odometer_km >= 0",
+            name="ck_bookings_start_odometer",
+        ),
+        CheckConstraint(
+            "end_odometer_km IS NULL OR end_odometer_km >= 0",
+            name="ck_bookings_end_odometer",
+        ),
+        Index("ix_bookings_vehicle_status_window", "vehicle_id", "status", "starts_at", "ends_at"),
+    )
 
     public_ref: Mapped[str] = mapped_column(String(20), unique=True, nullable=False)
     customer_id: Mapped[uuid.UUID] = mapped_column(