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_test.go

@@ -62,6 +62,22 @@ func TestAcceptanceAdmissionScopesLeaveProductionPolicyUnchanged(t *testing.T) {
 	}
 }
 
+func TestAsyncAdmissionBatchCoversCertifiedGlobalCapacity(t *testing.T) {
+	for _, testCase := range []struct {
+		globalHardLimit int
+		want            int
+	}{
+		{globalHardLimit: 48, want: 48},
+		{globalHardLimit: 64, want: 64},
+		{globalHardLimit: 128, want: 64},
+		{globalHardLimit: 0, want: 64},
+	} {
+		if got := asyncAdmissionBatchLimit(testCase.globalHardLimit); got != testCase.want {
+			t.Fatalf("async admission batch limit for %d = %d, want %d", testCase.globalHardLimit, got, testCase.want)
+		}
+	}
+}
+
 func TestPinCandidatesToTaskAdmissionPreservesAdmittedCandidate(t *testing.T) {
 	input := []store.RuntimeModelCandidate{
 		{PlatformID: "platform-a", PlatformModelID: "model-a"},