fix(acceptance): 使用可完整解码的 WebP 样本

替换截断的 WebP 验收夹具，新增全量图片像素解码回归，并保留 6K 外部水化与三参考图归一化测试，避免协议模拟样本缺陷被误判为 Worker 运行故障。\n\n验证：Go 全量测试、go vet、gofmt、git diff --check 通过。

apps/api/internal/runner/input_image_normalizer_test.go

@@ -8,6 +8,7 @@ import (
 	"image/color"
 	"image/jpeg"
 	"image/png"
+	"os"
 	"strings"
 	"testing"
 	"time"
@@ -147,6 +148,50 @@ func TestImageNormalizationSlotSerializesHeavyConversions(t *testing.T) {
 	}
 }
 
+func TestHydrateAndNormalizeExternalSixKReference(t *testing.T) {
+	fixtureURL := strings.TrimSpace(os.Getenv("AI_GATEWAY_TEST_VIDEO_FIXTURE_URL"))
+	if fixtureURL == "" {
+		t.Skip("set AI_GATEWAY_TEST_VIDEO_FIXTURE_URL to exercise a protocol fixture over HTTP")
+	}
+	service := &Service{imageNormalizeSlots: make(chan struct{}, 1)}
+	candidate := store.RuntimeModelCandidate{
+		Provider:       "volces",
+		PlatformConfig: map[string]any{"supportUrlInput": true, "supportBase64Input": true},
+		ModelType:      "omni_video",
+		Capabilities: map[string]any{
+			"omni_video": map[string]any{
+				"input_image_resolution_range": map[string]any{
+					"min": map[string]any{"long_edge": float64(300), "short_edge": float64(300)},
+					"max": map[string]any{"long_edge": float64(6000), "short_edge": float64(6000)},
+				},
+				"input_image_aspect_ratio_range": []any{float64(0.4), float64(2.5)},
+			},
+		},
+	}
+	content := make([]any, 0, 3)
+	for range 3 {
+		content = append(content, map[string]any{
+			"type": "image_url", "role": "reference_image",
+			"image_url": map[string]any{"url": fixtureURL},
+		})
+	}
+	body := map[string]any{"content": content}
+	hydrated, err := service.hydrateProviderRequestAssets(context.Background(), body, candidate)
+	if err != nil {
+		t.Fatal(err)
+	}
+	normalized, err := service.normalizeVideoInputImages(context.Background(), hydrated, candidate)
+	if err != nil {
+		t.Fatal(err)
+	}
+	for index, item := range normalized["content"].([]any) {
+		imageURL := item.(map[string]any)["image_url"].(map[string]any)["url"].(string)
+		if got := decodedImageSize(t, imageURL); got != image.Pt(6000, 2400) {
+			t.Fatalf("image %d has unexpected converted size: %v", index, got)
+		}
+	}
+}
+
 func TestNormalizeVideoInputImagesPadsAspectRatioViolation(t *testing.T) {
 	service := &Service{}
 	source := pngImageDataURL(t, 1530, 500)