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/cmd/acceptance-load/main_test.go

@@ -8,6 +8,7 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
+	"io"
 	"net/http"
 	"net/http/httptest"
 	"os"
@@ -82,6 +83,37 @@ func TestStreamGeminiRequestBodyPreservesInput(t *testing.T) {
 	}
 }
 
+func TestGeminiRequestBodyCanBeReplayedAfterHTTP2Failure(t *testing.T) {
+	input := paddedPNGVariant(256<<10, 91)
+	request, err := newGeminiRequest(t.Context(), "https://gateway.example/v1beta/models/test:generateContent", input)
+	if err != nil {
+		t.Fatalf("new Gemini request: %v", err)
+	}
+	if request.GetBody == nil {
+		t.Fatal("streaming Gemini request does not provide GetBody")
+	}
+	first, err := io.ReadAll(request.Body)
+	if err != nil {
+		t.Fatalf("read first request body: %v", err)
+	}
+	_ = request.Body.Close()
+	replayedBody, err := request.GetBody()
+	if err != nil {
+		t.Fatalf("replay Gemini request body: %v", err)
+	}
+	replayed, err := io.ReadAll(replayedBody)
+	if err != nil {
+		t.Fatalf("read replayed request body: %v", err)
+	}
+	_ = replayedBody.Close()
+	if !bytes.Equal(first, replayed) {
+		t.Fatal("replayed Gemini request body differs from the original")
+	}
+	if request.ContentLength != int64(len(first)) {
+		t.Fatalf("content length=%d, want %d", request.ContentLength, len(first))
+	}
+}
+
 func TestVideoCombinationsProvide128UniqueInputs(t *testing.T) {
 	images := make([]string, 16)
 	for index := range images {