fix(acceptance): 修复线上双站压测失真

将线上压力生成器拆分为宁波、香港宿主机上的 K3s 外进程，按全局序号分片并保守合并站点报告，避免操作者本机上行带宽成为容量瓶颈。\n\n为每次负载执行生成独立幂等键和 Run 级图片变体，阻止三轮验收重放旧任务或复用历史媒体缓存，并新增直接 OSS 物化一致性门禁。\n\n验证：Go 全量测试、go vet、迁移安全检查、bash -n、ShellCheck、manual-release-test 和双宿主机 linux/amd64 启动冒烟通过。

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

@@ -146,7 +146,7 @@ func TestGeminiLoadIsSplitAcrossTwoGatewayAPIs(t *testing.T) {
 		gateways: []string{first.URL, second.URL}, apiKeys: []string{"key-1", "key-2"}, runID: "run-1",
 		runToken: "token-1", geminiModel: "gemini-image-test",
 	}
-	result := runGemini(t.Context(), http.DefaultClient, opts, "dual-api", 8, 256<<10, 256<<10, false)
+	result := runGemini(t.Context(), http.DefaultClient, opts, "dual-api", 8, 256<<10, 256<<10, false, 0, 1)
 	if result.err != nil || result.report.Completed != 8 {
 		t.Fatalf("result=%+v err=%v", result.report, result.err)
 	}
@@ -158,6 +158,53 @@ func TestGeminiLoadIsSplitAcrossTwoGatewayAPIs(t *testing.T) {
 	}
 }
 
+func TestDistributedShardIndexesCoverWorkloadWithoutOverlap(t *testing.T) {
+	first := options{shardIndex: 0, shardCount: 2}
+	second := options{shardIndex: 1, shardCount: 2}
+	if first.shardRequestCount(1001) != 501 || second.shardRequestCount(1001) != 500 {
+		t.Fatalf("shard counts=%d/%d", first.shardRequestCount(1001), second.shardRequestCount(1001))
+	}
+	seen := map[int]bool{}
+	for local := 0; local < first.shardRequestCount(1001); local++ {
+		seen[first.logicalRequestIndex(local)] = true
+	}
+	for local := 0; local < second.shardRequestCount(1001); local++ {
+		index := second.logicalRequestIndex(local)
+		if seen[index] {
+			t.Fatalf("duplicate logical index %d", index)
+		}
+		seen[index] = true
+	}
+	if len(seen) != 1001 {
+		t.Fatalf("covered indexes=%d", len(seen))
+	}
+}
+
+func TestGeminiInputVariantIsRunScoped(t *testing.T) {
+	if geminiInputVariant("run-a", 7) == geminiInputVariant("run-b", 7) {
+		t.Fatal("different Run IDs produced the same input variant")
+	}
+	if geminiInputVariant("run-a", 7) == geminiInputVariant("run-a", 8) {
+		t.Fatal("different logical indexes produced the same input variant")
+	}
+}
+
+func TestAcceptanceIdempotencyKeyIncludesExecutionAndLogicalIndex(t *testing.T) {
+	request := httptest.NewRequest(http.MethodPost, "https://gateway.example/v1", nil)
+	opts := options{
+		apiKeys: []string{"key-1"}, runID: "run-1", runToken: "token-1", executionID: "p24-2-gemini-baseline",
+	}
+	opts.setHeaders(request, 17, false)
+	if got := request.Header.Get("Idempotency-Key"); got != "acceptance-run-1-p24-2-gemini-baseline-17" {
+		t.Fatalf("idempotency key=%q", got)
+	}
+	poll := httptest.NewRequest(http.MethodGet, "https://gateway.example/result", nil)
+	opts.setHeaders(poll, 17, false)
+	if got := poll.Header.Get("Idempotency-Key"); got != "" {
+		t.Fatalf("GET request unexpectedly has idempotency key %q", got)
+	}
+}
+
 func TestValidateVideoAssetDownloadsFinalMedia(t *testing.T) {
 	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, request *http.Request) {
 		if request.Header.Get("Authorization") != "" {