fix: preserve source aspect for alibaba auto size

lib/ai/providers/alibaba-image.ts

@@ -120,6 +120,79 @@ async function inferAspectRatioFromImageUrl(imageUrl: string): Promise<number |
   }
 }
 
+async function inferImageDimensionsFromImageUrl(
+  imageUrl: string,
+): Promise<{ width: number; height: number; aspectRatio: number } | null> {
+  if (!/^https?:\/\//i.test(imageUrl)) return null;
+
+  const controller = new AbortController();
+  const timeoutId = setTimeout(() => controller.abort(), ALIBABA_IMAGE_FETCH_TIMEOUT_MS);
+  try {
+    const response = await fetch(imageUrl, { signal: controller.signal });
+    if (!response.ok) {
+      console.warn("[Alibaba Image] Failed to fetch reference image dimensions:", response.status);
+      return null;
+    }
+
+    const buffer = Buffer.from(await response.arrayBuffer());
+    if (!buffer.length) return null;
+
+    const metadata = await sharp(buffer).metadata();
+    if (!metadata.width || !metadata.height || metadata.height <= 0) return null;
+
+    return {
+      width: metadata.width,
+      height: metadata.height,
+      aspectRatio: metadata.width / metadata.height,
+    };
+  } catch (error) {
+    console.warn("[Alibaba Image] Failed to infer image dimensions from reference image:", error);
+    return null;
+  } finally {
+    clearTimeout(timeoutId);
+  }
+}
+
+function calculateAlibabaSizeFromDimensions(
+  width: number,
+  height: number,
+  baseSize: number,
+): string {
+  const safeWidth = Math.max(1, Math.round(width));
+  const safeHeight = Math.max(1, Math.round(height));
+  const longestSide = Math.max(safeWidth, safeHeight);
+  const scale = baseSize / longestSide;
+
+  let scaledWidth = Math.round(safeWidth * scale);
+  let scaledHeight = Math.round(safeHeight * scale);
+
+  if (scaledWidth > ALIBABA_MAX_SIZE || scaledHeight > ALIBABA_MAX_SIZE) {
+    const clampScale = Math.min(
+      ALIBABA_MAX_SIZE / scaledWidth,
+      ALIBABA_MAX_SIZE / scaledHeight,
+    );
+    scaledWidth = Math.round(scaledWidth * clampScale);
+    scaledHeight = Math.round(scaledHeight * clampScale);
+  }
+
+  if (scaledWidth < ALIBABA_MIN_SIZE || scaledHeight < ALIBABA_MIN_SIZE) {
+    const boostScale = Math.max(
+      ALIBABA_MIN_SIZE / scaledWidth,
+      ALIBABA_MIN_SIZE / scaledHeight,
+    );
+    scaledWidth = Math.round(scaledWidth * boostScale);
+    scaledHeight = Math.round(scaledHeight * boostScale);
+  }
+
+  scaledWidth = Math.max(ALIBABA_MIN_SIZE, Math.min(ALIBABA_MAX_SIZE, scaledWidth));
+  scaledHeight = Math.max(ALIBABA_MIN_SIZE, Math.min(ALIBABA_MAX_SIZE, scaledHeight));
+
+  scaledWidth = Math.round(scaledWidth / 2) * 2;
+  scaledHeight = Math.round(scaledHeight / 2) * 2;
+
+  return `${scaledWidth}*${scaledHeight}`;
+}
+
 /**
  * 创建缩略图
  */
@@ -501,17 +574,29 @@ export function createAlibabaImage({ apiKey, baseURL }: AlibabaImageConfig) {
             if (aspectRatio === "auto") {
               // 阿里文档在 auto 下默认接近 1024*1024，这会让 4K 选择失效。
               // 这里改为根据参考图比例计算 size，确保 1K/2K/4K 档位真正生效。
-              const referenceImageUrl = imageUrls[imageUrls.length - 1];
-              const inferredAspectRatio = await inferAspectRatioFromImageUrl(referenceImageUrl);
-              if (inferredAspectRatio) {
-                params.size = calculateAlibabaSizeByAspect(inferredAspectRatio, baseSize);
+              const referenceImageUrl = imageUrls[0];
+              const inferredDimensions = await inferImageDimensionsFromImageUrl(referenceImageUrl);
+              if (inferredDimensions) {
+                params.size = calculateAlibabaSizeFromDimensions(
+                  inferredDimensions.width,
+                  inferredDimensions.height,
+                  baseSize,
+                );
                 console.log(
-                  `[Alibaba Image] Auto mode resolved size: imageSize=${imageSize}, inferredAspect=${inferredAspectRatio} => size=${params.size}`
+                  `[Alibaba Image] Auto mode resolved size: imageSize=${imageSize}, reference=${inferredDimensions.width}x${inferredDimensions.height}, inferredAspect=${inferredDimensions.aspectRatio} => size=${params.size}`
                 );
               } else {
-                console.log(
-                  `[Alibaba Image] Auto mode keeps provider default size: imageSize=${imageSize}, inferredAspect=unavailable`
-                );
+                const inferredAspectRatio = await inferAspectRatioFromImageUrl(referenceImageUrl);
+                if (inferredAspectRatio) {
+                  params.size = calculateAlibabaSizeByAspect(inferredAspectRatio, baseSize);
+                  console.log(
+                    `[Alibaba Image] Auto mode resolved size via aspect fallback: imageSize=${imageSize}, inferredAspect=${inferredAspectRatio} => size=${params.size}`
+                  );
+                } else {
+                  console.log(
+                    `[Alibaba Image] Auto mode keeps provider default size: imageSize=${imageSize}, inferredAspect=unavailable`
+                  );
+                }
               }
             } else {
               const calculatedSize = calculateSize(aspectRatio, baseSize);