fix(acceptance): 解除八任务准入瓶颈

线上 P24 验收证明 Worker 注册容量为 48，但异步 admission 始终只有 8 条活跃租约。将单事务调度窗口覆盖当前 2 x P32 的 64 槽，避免多 Worker 在同一 FIFO 小批次上竞争形成隐性全局上限。\n\nGemini 流式请求补充可回放 GetBody 与精确 Content-Length，使带幂等键的 POST 遇到 HTTP/2 可重试传输错误时可安全重放；同时提前部署验收回调收集器，保证旧 Run side effects 能在接管前收口。\n\n已通过 Go 全量测试、go vet、gofmt、Shell bash -n、ShellCheck、验收与人工发布脚本测试、迁移安全检查，以及独立 PostgreSQL 48 条 admission/租约/River job 原子集成测试。

apps/api/internal/runner/admission.go

@@ -33,7 +33,11 @@ const (
 	asyncWorkerCapacityScopeKey = "global"
 	asyncWorkerQueueLimit       = 10000
 	asyncWorkerMaxWaitSeconds   = 24 * 60 * 60
-	asyncAdmissionBatchMax      = 8
+	// One transaction must be able to fill the certified 2 x P32 global
+	// capacity. Smaller windows let multiple Worker dispatchers repeatedly race
+	// on the same FIFO head and can turn a batch size into an accidental cluster
+	// concurrency ceiling.
+	asyncAdmissionBatchMax      = 64
 	acceptanceQueueLimit        = 10000
 	acceptanceQueueMaxWait      = 15 * 60
 	synchronousAdmissionWakeMax = 256
@@ -737,13 +741,7 @@ func (s *Service) dispatchWaitingAsyncAdmissions(ctx context.Context) {
 		case <-ticker.C:
 		}
 		for {
-			batchLimit := s.cfg.AsyncWorkerHardLimit
-			if batchLimit <= 0 {
-				batchLimit = 64
-			}
-			if batchLimit > asyncAdmissionBatchMax {
-				batchLimit = asyncAdmissionBatchMax
-			}
+			batchLimit := asyncAdmissionBatchLimit(s.cfg.AsyncWorkerHardLimit)
 			taskIDs, err := s.store.ListWaitingAsyncAdmissionTaskIDs(ctx, batchLimit)
 			if err != nil {
 				s.logger.Warn("list waiting async admissions failed", "error", err)
@@ -789,6 +787,13 @@ func (s *Service) dispatchWaitingAsyncAdmissions(ctx context.Context) {
 	}
 }
 
+func asyncAdmissionBatchLimit(globalHardLimit int) int {
+	if globalHardLimit <= 0 || globalHardLimit > asyncAdmissionBatchMax {
+		return asyncAdmissionBatchMax
+	}
+	return globalHardLimit
+}
+
 func (s *Service) reapExpiredTaskAdmissions(ctx context.Context) {
 	ticker := time.NewTicker(5 * time.Second)
 	defer ticker.Stop()