Documenting CASCADE delete for orphaned variations

Tests that variations are automatically deleted when their parent
product is deleted due to foreign key constraints with CASCADE delete.

This documents that the noParentProductForVariation error thrown in
searchVariationByGlobalUniqueID is defensive code that won't be
triggered in normal operation, since the database prevents orphaned
variations from existing.

Author: joshheald

Modules/Tests/YosemiteTests/PointOfSale/PointOfSaleLocalBarcodeScanServiceTests.swift

@@ -219,6 +219,67 @@ struct PointOfSaleLocalBarcodeScanServiceTests {
         }
     }
 
+    @Test("Foreign key constraint prevents orphaned variations")
+    func test_variations_cannot_be_orphaned() async throws {
+        // Given
+        let barcode = "ORPHAN-VAR-123"
+
+        // Insert a parent product
+        let parentProduct = PersistedProduct(
+            id: 888,
+            siteID: siteID,
+            name: "Parent Product",
+            productTypeKey: "variable",
+            fullDescription: nil,
+            shortDescription: nil,
+            sku: nil,
+            globalUniqueID: nil,
+            price: "0.00",
+            downloadable: false,
+            parentID: 0,
+            manageStock: false,
+            stockQuantity: nil,
+            stockStatusKey: "instock"
+        )
+        try await insertProduct(parentProduct)
+
+        // Insert the variation
+        let variation = PersistedProductVariation(
+            id: 999,
+            siteID: siteID,
+            productID: 888,
+            sku: nil,
+            globalUniqueID: barcode,
+            price: "20.00",
+            downloadable: false,
+            fullDescription: nil,
+            manageStock: false,
+            stockQuantity: nil,
+            stockStatusKey: "instock"
+        )
+        try await insertVariation(variation)
+
+        // Verify the variation exists
+        let variationExists = try await grdbManager.databaseConnection.read { db in
+            try PersistedProductVariation.fetchOne(db, key: ["siteID": siteID, "id": 999]) != nil
+        }
+        #expect(variationExists, "Variation should exist after insertion")
+
+        // When - Delete the parent product (with foreign keys enabled)
+        try await grdbManager.databaseConnection.write { db in
+            try db.execute(sql: "DELETE FROM product WHERE id = ? AND siteID = ?", arguments: [888, siteID])
+        }
+
+        // Then - Variation should be automatically deleted by CASCADE
+        let variationStillExists = try await grdbManager.databaseConnection.read { db in
+            try PersistedProductVariation.fetchOne(db, key: ["siteID": siteID, "id": 999]) != nil
+        }
+        #expect(!variationStillExists, "Variation should be automatically deleted by CASCADE when parent is deleted")
+
+        // This means the noParentProductForVariation error is defensive code that won't be triggered
+        // in normal operation due to foreign key constraints with CASCADE delete
+    }
+
     // MARK: - Helper Methods
 
     private func insertProduct(_ product: PersistedProduct) async throws {