feat: harden downstream requeue tasks

api/prisma/migrations/20260813150000_harden_downstream_requeue_tasks/migration.sql

@@ -0,0 +1,19 @@
+ALTER TABLE "DownstreamRequeueTask"
+  ADD COLUMN "applicationFailures" JSONB NOT NULL DEFAULT '{}',
+  ADD COLUMN "scanLeaseOwner" TEXT,
+  ADD COLUMN "scanLeaseUntil" TIMESTAMP(3);
+
+CREATE TABLE "DownstreamRequeueRateWindow" (
+  "id" TEXT NOT NULL,
+  "applicationId" TEXT NOT NULL,
+  "windowStartedAt" TIMESTAMP(3) NOT NULL,
+  "consumed" INTEGER NOT NULL DEFAULT 0,
+  "updatedAt" TIMESTAMP(3) NOT NULL,
+  "createdAt" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+  CONSTRAINT "DownstreamRequeueRateWindow_pkey" PRIMARY KEY ("id")
+);
+
+CREATE UNIQUE INDEX "DownstreamRequeueRateWindow_applicationId_windowStartedAt_key"
+  ON "DownstreamRequeueRateWindow"("applicationId", "windowStartedAt");
+CREATE INDEX "DownstreamRequeueRateWindow_windowStartedAt_idx"
+  ON "DownstreamRequeueRateWindow"("windowStartedAt");

api/prisma/schema.prisma

@@ -2137,7 +2137,10 @@ model DownstreamRequeueTask {
   skippedCount            Int       @default(0)
   waitingCount            Int       @default(0)
   consecutiveFailures     Int       @default(0)
+  applicationFailures     Json      @default("{}")
   lastError               String?
+  scanLeaseOwner          String?
+  scanLeaseUntil          DateTime?
   createdById             String?
   startedAt               DateTime?
   pausedAt                DateTime?
@@ -2155,6 +2158,18 @@ model DownstreamRequeueTask {
   @@index([tenantId, createdAt])
 }
 
+model DownstreamRequeueRateWindow {
+  id              String   @id @default(cuid())
+  applicationId   String
+  windowStartedAt DateTime
+  consumed        Int      @default(0)
+  updatedAt       DateTime @updatedAt
+  createdAt       DateTime @default(now())
+
+  @@unique([applicationId, windowStartedAt])
+  @@index([windowStartedAt])
+}
+
 model DownstreamRequeueTaskItem {
   id             String    @id @default(cuid())
   taskId         String