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.go

@@ -37,6 +37,11 @@ const (
 	upstreamHeader = "X-EasyAI-Acceptance-Upstream"
 )
 
+const (
+	geminiRequestPrefix = `{"contents":[{"role":"user","parts":[{"text":"将参考图编辑为蓝色赛博朋克风格，保留主体结构"},{"inlineData":{"mimeType":"image/png","data":"`
+	geminiRequestSuffix = `"}}]}],"generationConfig":{"responseModalities":["IMAGE"]}}`
+)
+
 var reportURLPattern = regexp.MustCompile(`(?i)(?:https?|postgres(?:ql)?):\/\/[^\s"'<>]+`)
 
 type options struct {
@@ -407,16 +412,8 @@ func runGemini(
 			defer func() { <-slots }()
 			requestStarted := time.Now()
 			endpoint := opts.gateways[logicalIndex%len(opts.gateways)] + "/v1beta/models/" + url.PathEscape(opts.geminiModel) + ":generateContent"
-			requestBody := streamGeminiRequestBody(paddedPNGVariant(inputBytes, geminiInputVariant(opts.runID+"/"+opts.executionID, logicalIndex)))
-			req, err := http.NewRequestWithContext(
-				ctx,
-				http.MethodPost,
-				endpoint,
-				requestBody,
-			)
-			if err != nil {
-				_ = requestBody.Close()
-			}
+			input := paddedPNGVariant(inputBytes, geminiInputVariant(opts.runID+"/"+opts.executionID, logicalIndex))
+			req, err := newGeminiRequest(ctx, endpoint, input)
 			if err == nil {
 				opts.setHeaders(req, logicalIndex, realUpstream)
 				req.Header.Set("Content-Type", "application/json")
@@ -481,7 +478,7 @@ func streamGeminiRequestBody(input []byte) io.ReadCloser {
 		closeWithError := func(err error) {
 			_ = writer.CloseWithError(err)
 		}
-		if _, err := io.WriteString(writer, `{"contents":[{"role":"user","parts":[{"text":"将参考图编辑为蓝色赛博朋克风格，保留主体结构"},{"inlineData":{"mimeType":"image/png","data":"`); err != nil {
+		if _, err := io.WriteString(writer, geminiRequestPrefix); err != nil {
 			closeWithError(err)
 			return
 		}
@@ -494,7 +491,7 @@ func streamGeminiRequestBody(input []byte) io.ReadCloser {
 			closeWithError(err)
 			return
 		}
-		if _, err := io.WriteString(writer, `"}}]}],"generationConfig":{"responseModalities":["IMAGE"]}}`); err != nil {
+		if _, err := io.WriteString(writer, geminiRequestSuffix); err != nil {
 			closeWithError(err)
 			return
 		}
@@ -503,6 +500,21 @@ func streamGeminiRequestBody(input []byte) io.ReadCloser {
 	return reader
 }
 
+func newGeminiRequest(ctx context.Context, endpoint string, input []byte) (*http.Request, error) {
+	getBody := func() (io.ReadCloser, error) {
+		return streamGeminiRequestBody(input), nil
+	}
+	body, _ := getBody()
+	request, err := http.NewRequestWithContext(ctx, http.MethodPost, endpoint, body)
+	if err != nil {
+		_ = body.Close()
+		return nil, err
+	}
+	request.GetBody = getBody
+	request.ContentLength = int64(len(geminiRequestPrefix) + base64.StdEncoding.EncodedLen(len(input)) + len(geminiRequestSuffix))
+	return request, nil
+}
+
 func runVideo(
 	ctx context.Context,
 	client *http.Client,