fix: improve scale adjust annotation guide

app/api/canvas/local-edit/route.ts

@@ -931,7 +931,7 @@ function buildScaleAdjustPrompt(
     "这是一项局部主体比例 inpaint/edit 任务，不是整图缩放、整图裁切或重新构图任务。",
     sourceSizeLine,
     "输入图片1是原始干净图，也是最终输出必须继承的唯一画面基底。除目标主体尺寸变化与必要背景补全外，输入图片1中的文字、Logo、装饰、排版、背景、光线、构图边界和所有未选区域必须保持不变。",
-    "输入图片2是白底选区参考图，只用于说明输入图片1上的红色实线框、青色目标虚线框和四角箭头关系；它不包含场景内容，不是输出底图，不得学习或复刻它的框线、箭头、编号、角点、半透明遮罩或 UI 标记。",
+    "输入图片2是输入图片1的标注副本，直接在原始图上叠加了红色实线框、青色目标虚线框和四角箭头，只用于让你读取目标主体的当前位置、目标大小和目标位置；输入图片2不是输出底图，不得学习或复刻它的框线、箭头、编号、角点、半透明遮罩或 UI 标记。",
     cropLines
       ? `输入图片3及之后是框选区域的干净局部裁切参考图，作用是帮助你确认“要缩放的是哪个主体”。这些裁切图不是输出底图，不得被整体放大、贴回或覆盖到原图上。\n${cropLines}`
       : "",
@@ -1099,16 +1099,7 @@ export async function POST(request: NextRequest) {
           regions,
           width: sourceWidth,
         });
-    const annotatedBase = isScaleAdjustOperation
-      ? sharp({
-          create: {
-            background: "#ffffff",
-            channels: 3,
-            height: sourceHeight,
-            width: sourceWidth,
-          },
-        })
-      : sharp(sourceBuffer, { failOn: "none" });
+    const annotatedBase = sharp(sourceBuffer, { failOn: "none" });
     const annotatedBuffer = await annotatedBase
       .composite([{ input: annotationSvg, left: 0, top: 0 }])
       .png({ compressionLevel: 6 })
@@ -1194,7 +1185,7 @@ export async function POST(request: NextRequest) {
         annotatedReferenceUrl: annotatedUpload.url,
         annotatedReferenceSentToModel: isScaleAdjustOperation,
         annotatedReferenceType: isScaleAdjustOperation
-          ? "white-source-target-arrow-guide"
+          ? "source-target-arrow-overlay"
           : "source-overlay",
         cleanSourceReferenceIndex: 1,
         configuredDetailModelId: configuredDetailModel || null,
@@ -1218,7 +1209,7 @@ export async function POST(request: NextRequest) {
         scaleAdjustTargetRegionCount: regions.filter((region) => region.targetRect)
           .length,
         scaleAdjustPromptStrategy: isScaleAdjustOperation
-          ? "locked-plate-local-subject-target-box-arrows-v5"
+          ? "locked-plate-local-subject-target-box-arrows-v6"
           : undefined,
         scaleAdjustPostCompositeApplied: false,
         scaleAdjustUsesFullFrameOutput: isScaleAdjustOperation,