M34: enforce domain integrity in PostgreSQL

backend/app/models/data_quality.py

@@ -2,7 +2,7 @@ import uuid
 from datetime import datetime
 from typing import TYPE_CHECKING
 
-from sqlalchemy import DateTime, ForeignKey, String
+from sqlalchemy import CheckConstraint, DateTime, ForeignKey, Index, String
 from sqlalchemy.dialects.postgresql import JSONB, UUID
 from sqlalchemy.orm import Mapped, mapped_column, relationship
 
@@ -25,6 +25,19 @@ ISSUE_STATUSES = ("open", "deferred", "resolved", "rejected")
 
 class DataQualityIssue(UUIDPrimaryKeyMixin, TimestampMixin, Base):
     __tablename__ = "data_quality_issues"
+    __table_args__ = (
+        CheckConstraint(
+            "rule_type IN ('possible_duplicate_customer','missing_required_field',"
+            "'odometer_regression','booking_overlap','vehicle_status_conflict')",
+            name="ck_data_quality_rule_type",
+        ),
+        CheckConstraint("severity IN ('low','medium','high')", name="ck_data_quality_severity"),
+        CheckConstraint(
+            "status IN ('open','deferred','resolved','rejected')",
+            name="ck_data_quality_status",
+        ),
+        Index("ix_data_quality_work_queue", "status", "due_at", "severity"),
+    )
 
     public_ref: Mapped[str] = mapped_column(String(20), unique=True, nullable=False)
     rule_type: Mapped[str] = mapped_column(String(40), nullable=False)