perf(acceptance): 流式生成唯一图片输入

避免千请求验收重复复用同一图片内容而争用同一资产记录，使每个任务走真实独立上传与物化链路。\n\nGemini 请求体改为流式 Base64 编码，降低压测客户端的大对象内存峰值；新增尺寸、哈希唯一性和请求体还原测试。\n\n验证：Go 全量测试、go vet、迁移安全检查、bash -n、ShellCheck、gofmt、git diff --check 均通过。

apps/api/cmd/acceptance-load/main.go

@@ -247,20 +247,6 @@ func runGemini(
 	realUpstream bool,
 ) phaseResult {
 	startedAt := time.Now()
-	input := paddedPNG(inputBytes)
-	requestBody, _ := json.Marshal(map[string]any{
-		"contents": []any{map[string]any{
-			"role": "user",
-			"parts": []any{
-				map[string]any{"text": "将参考图编辑为蓝色赛博朋克风格，保留主体结构"},
-				map[string]any{"inlineData": map[string]any{
-					"mimeType": "image/png",
-					"data":     base64.StdEncoding.EncodeToString(input),
-				}},
-			},
-		}},
-		"generationConfig": map[string]any{"responseModalities": []any{"IMAGE"}},
-	})
 	expectedHash := ""
 	if expectedOutputBytes > 0 {
 		sum := sha256.Sum256(paddedPNG(expectedOutputBytes))
@@ -287,7 +273,16 @@ func runGemini(
 			defer func() { <-slots }()
 			requestStarted := time.Now()
 			endpoint := opts.gateways[index%len(opts.gateways)] + "/v1beta/models/" + url.PathEscape(opts.geminiModel) + ":generateContent"
-			req, err := http.NewRequestWithContext(ctx, http.MethodPost, endpoint, bytes.NewReader(requestBody))
+			requestBody := streamGeminiRequestBody(paddedPNGVariant(inputBytes, index+1))
+			req, err := http.NewRequestWithContext(
+				ctx,
+				http.MethodPost,
+				endpoint,
+				requestBody,
+			)
+			if err != nil {
+				_ = requestBody.Close()
+			}
 			if err == nil {
 				opts.setHeaders(req, index, realUpstream)
 				req.Header.Set("Content-Type", "application/json")
@@ -344,6 +339,34 @@ func runGemini(
 	return phaseResult{report: result, latencies: latencies, err: firstErr}
 }
 
+func streamGeminiRequestBody(input []byte) io.ReadCloser {
+	reader, writer := io.Pipe()
+	go func() {
+		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 {
+			closeWithError(err)
+			return
+		}
+		encoder := base64.NewEncoder(base64.StdEncoding, writer)
+		if _, err := encoder.Write(input); err != nil {
+			closeWithError(err)
+			return
+		}
+		if err := encoder.Close(); err != nil {
+			closeWithError(err)
+			return
+		}
+		if _, err := io.WriteString(writer, `"}}]}],"generationConfig":{"responseModalities":["IMAGE"]}}`); err != nil {
+			closeWithError(err)
+			return
+		}
+		_ = writer.Close()
+	}()
+	return reader
+}
+
 func runVideo(
 	ctx context.Context,
 	client *http.Client,
@@ -778,6 +801,10 @@ func percentileMilliseconds(values []time.Duration, quantile float64) float64 {
 }
 
 func paddedPNG(size int) []byte {
+	return paddedPNGVariant(size, 0)
+}
+
+func paddedPNGVariant(size int, variant int) []byte {
 	base, _ := base64.StdEncoding.DecodeString("iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAQAAAC1HAwCAAAAC0lEQVR42mNk+A8AAQUBAScY42YAAAAASUVORK5CYII=")
 	if size <= len(base) {
 		return base
@@ -790,6 +817,9 @@ func paddedPNG(size int) []byte {
 	chunk := make([]byte, 12+paddingLength)
 	binary.BigEndian.PutUint32(chunk[:4], uint32(paddingLength))
 	copy(chunk[4:8], []byte("teST"))
+	if variant != 0 && paddingLength >= 8 {
+		binary.BigEndian.PutUint64(chunk[8:16], uint64(variant))
+	}
 	binary.BigEndian.PutUint32(chunk[8+paddingLength:], crc32.ChecksumIEEE(chunk[4:8+paddingLength]))
 	out := make([]byte, 0, size)
 	out = append(out, base[:iendOffset]...)