fix: race condition in getExternalDbSyncFusebox

getExternalDbFusebox used to lazy init the settings singleton.
However, this caused issues.
Prisma's upsert isn't safe from race conditions.
So this could cause collisions/ unique key issues.
Get doesn't need to update anything. Let's just return default values and have the update handle the init.
Tested on local that fusebox updates work fine.

Author: nams1570

apps/backend/src/lib/external-db-sync-metadata.ts

@@ -11,18 +11,25 @@ const fuseboxSelect = {
   pollerEnabled: true,
 };
 
+// Default values match the Prisma schema defaults
+const defaultFusebox: ExternalDbSyncFusebox = {
+  sequencerEnabled: true,
+  pollerEnabled: true,
+};
+
 export async function getExternalDbSyncFusebox(): Promise<ExternalDbSyncFusebox> {
-  return await globalPrismaClient.externalDbSyncMetadata.upsert({
+  const result = await globalPrismaClient.externalDbSyncMetadata.findFirst({
     where: { singleton: BooleanTrue.TRUE },
-    create: { singleton: BooleanTrue.TRUE },
-    update: {},
     select: fuseboxSelect,
   });
+  // Return defaults if row doesn't exist yet (row is created on first update)
+  return result ?? defaultFusebox;
 }
 
 export async function updateExternalDbSyncFusebox(
   updates: ExternalDbSyncFusebox,
 ): Promise<ExternalDbSyncFusebox> {
+  // Upsert is fine here - updates are infrequent and typically manual/admin actions
   return await globalPrismaClient.externalDbSyncMetadata.upsert({
     where: { singleton: BooleanTrue.TRUE },
     create: { singleton: BooleanTrue.TRUE, ...updates },