Implement display artifacts, pricing integrity, draft base and publish preview bundle

backend/app/repositories/pricing.py

@@ -9,6 +9,34 @@ from app.models.price_rule import PriceRuleRecord
 from app.models.pricing_category import PricingCategoryRecord
 
 
+async def _ensure_unique_price_rule_target(
+    *,
+    session,
+    scheme_id: str,
+    target_type: str,
+    target_ref: str,
+    exclude_price_rule_id: str | None = None,
+) -> None:
+    stmt = select(PriceRuleRecord).where(
+        PriceRuleRecord.scheme_id == scheme_id,
+        PriceRuleRecord.target_type == target_type,
+        PriceRuleRecord.target_ref == target_ref,
+    )
+    result = await session.execute(stmt)
+    row = result.scalar_one_or_none()
+
+    if row is None:
+        return
+
+    if exclude_price_rule_id and row.price_rule_id == exclude_price_rule_id:
+        return
+
+    raise HTTPException(
+        status_code=status.HTTP_409_CONFLICT,
+        detail="Pricing rule already exists for this target",
+    )
+
+
 async def create_pricing_category(
     *,
     scheme_id: str,
@@ -96,6 +124,13 @@ async def create_price_rule(
     price_rule_id = uuid4().hex
 
     async with AsyncSessionLocal() as session:
+        await _ensure_unique_price_rule_target(
+            session=session,
+            scheme_id=scheme_id,
+            target_type=target_type,
+            target_ref=target_ref,
+        )
+
         row = PriceRuleRecord(
             price_rule_id=price_rule_id,
             scheme_id=scheme_id,
@@ -136,6 +171,14 @@ async def update_price_rule(
                 detail="Price rule not found",
             )
 
+        await _ensure_unique_price_rule_target(
+            session=session,
+            scheme_id=scheme_id,
+            target_type=target_type,
+            target_ref=target_ref,
+            exclude_price_rule_id=price_rule_id,
+        )
+
         row.pricing_category_id = pricing_category_id
         row.target_type = target_type
         row.target_ref = target_ref