fix: handle fast-completion race in StreamBatchItemsService count check

When all batch runs complete before getBatchEnqueuedCount() is called,
cleanup() has already deleted the enqueuedItemsKey in Redis, causing it
to return 0. The existing Postgres fallback only checked sealed, but the
BatchQueue completion path sets status=COMPLETED without setting
sealed=true. Add the status check so the endpoint returns sealed:true
instead of triggering SDK retries into a dead BatchQueue.

Also switch findUnique to findFirst per webapp convention.

Author: matt-aitken

apps/webapp/app/runEngine/services/streamBatchItems.server.ts

@@ -212,15 +212,18 @@ export class StreamBatchItemsService extends WithRunEngine {
         // Validate we received the expected number of items
         if (enqueuedCount !== batch.runCount) {
           // The batch queue consumers may have already processed all items and
-          // cleaned up the Redis keys before we got here (especially likely when
-          // items include pre-failed runs that complete instantly). Check if the
-          // batch was already sealed/completed in Postgres.
-          const currentBatch = await this._prisma.batchTaskRun.findUnique({
+          // cleaned up the Redis keys before we got here. This happens when all
+          // runs complete fast enough that cleanup() deletes the enqueuedItemsKey
+          // before we read it — typically when the last item executes in the
+          // milliseconds between the loop ending and getBatchEnqueuedCount() being called.
+          // Check both sealed (sealed by this endpoint on a concurrent request) and
+          // COMPLETED (sealed by the BatchQueue completion path before we got here).
+          const currentBatch = await this._prisma.batchTaskRun.findFirst({
             where: { id: batchId },
             select: { sealed: true, status: true },
           });
 
-          if (currentBatch?.sealed) {
+          if (currentBatch?.sealed || currentBatch?.status === "COMPLETED") {
             logger.info("Batch already sealed before count check (fast completion)", {
               batchId: batchFriendlyId,
               itemsAccepted,