fix(db): add index to ProjectAlertStorage to prevent sequence scans

Author: ericallam

internal-packages/database/prisma/migrations/20260409120000_add_project_alert_storage_lookup_index/migration.sql

@@ -0,0 +1,2 @@
+-- CreateIndex
+CREATE INDEX CONCURRENTLY IF NOT EXISTS "ProjectAlertStorage_alertChannelId_alertType_storageId_idx" ON "ProjectAlertStorage"("alertChannelId", "alertType", "storageId");

internal-packages/database/prisma/schema.prisma

@@ -2198,6 +2198,8 @@ model ProjectAlertStorage {
 
   createdAt DateTime @default(now())
   updatedAt DateTime @updatedAt
+
+  @@index([alertChannelId, alertType, storageId])
 }
 
 model OrganizationIntegration {