feat(scene-fusion): enforce pre-rmbg for random mode and add agent background prompt enhancement

app/api/scene-fusion/route.ts

@@ -23,6 +23,7 @@ import { callQwen3Vl } from "@/lib/ai/qwen3-vl";
 const sceneFusionRequestSchema = z.object({
   productImage: z.string().min(1, "产品图不能为空"),
   productName: z.string().optional(), // 产品名称（如"沙发"）
+  sceneMode: z.enum(["scene-fission", "multi-product-scene", "random-bg"]).optional(),
   aspectRatio: z.string().optional(), // 图片比例（如"1:1", "4:3", "auto"）
   imageSize: z.string().optional(), // 图片分辨率（如"1K", "2K", "4K"）
   scenes: z.array(z.object({
@@ -395,6 +396,133 @@ async function detectTargetNameWithAgent(
   return { name, confidence, model };
 }
 
+function extractStyleHintFromPrompt(customPrompt: string | undefined): string | undefined {
+  const content = String(customPrompt || "").trim();
+  if (!content) return undefined;
+  const quoted = content.match(/[“"]([^”"]+?)(?:风格|场景)/);
+  if (quoted?.[1]) {
+    return normalizeSceneFusionName(quoted[1]) || quoted[1].trim();
+  }
+  const styleOnly = content.match(/(?:替换背景为|背景为|风格为)\s*([^，。；]+)/);
+  if (styleOnly?.[1]) {
+    return normalizeSceneFusionName(styleOnly[1]) || styleOnly[1].trim();
+  }
+  return undefined;
+}
+
+function mergeCustomPrompt(basePrompt: string | undefined, addition: string | undefined): string | undefined {
+  const base = String(basePrompt || "").trim();
+  const extra = String(addition || "").trim();
+  if (!base && !extra) return undefined;
+  if (!base) return extra.slice(0, 280);
+  if (!extra) return base.slice(0, 280);
+  if (base.includes(extra)) return base.slice(0, 280);
+  if (extra.includes(base)) return extra.slice(0, 280);
+  return `${base} ${extra}`.slice(0, 280);
+}
+
+async function generateRandomBackgroundPromptWithAgent(params: {
+  productImageUrl: string;
+  productNameHint?: string;
+  styleHint?: string;
+  userPrompt?: string;
+}): Promise<string | null> {
+  const prompt = [
+    "你是电商场景策划助手。",
+    `产品名称：${params.productNameHint || "该产品"}`,
+    params.styleHint ? `期望风格：${params.styleHint}` : "",
+    params.userPrompt ? `用户补充要求：${params.userPrompt}` : "",
+    "请基于产品图生成一条“仅描述背景场景”的中文提示词。",
+    "要求：",
+    "- 场景必须与产品品类匹配，适合商品展示",
+    "- 只描述背景、灯光、材质氛围，不改动产品主体外观",
+    "- 不要输出流程指令（例如“替换背景/保持主体”）",
+    "- 20~60字，语义具体可执行",
+    "仅返回 JSON：",
+    "{\"backgroundPrompt\":\"...\"}",
+  ]
+    .filter(Boolean)
+    .join("\n");
+
+  const { text } = await callQwen3Vl({
+    imageUrl: params.productImageUrl,
+    prompt,
+    temperature: 0.2,
+    maxTokens: 240,
+    timeoutMs: SCENE_FUSION_AGENT_TIMEOUT_MS,
+    retries: 1,
+  });
+
+  const parsed = extractJsonObject(text);
+  const backgroundPromptRaw = String(parsed?.backgroundPrompt || "").replace(/\s+/g, " ").trim();
+  if (!backgroundPromptRaw || backgroundPromptRaw.length < 6) {
+    return null;
+  }
+  return backgroundPromptRaw.slice(0, 120);
+}
+
+async function enrichRandomBackgroundScenesWithAgent(params: {
+  requestId: string;
+  productImageUrl: string;
+  productName?: string;
+  scenes: Array<{
+    id: string;
+    image: string;
+    targetName?: string;
+    customPrompt?: string;
+    imageUrl: string;
+  }>;
+}): Promise<Array<{
+  id: string;
+  image: string;
+  targetName?: string;
+  customPrompt?: string;
+  imageUrl: string;
+}>> {
+  const nextScenes = params.scenes.map((scene) => ({ ...scene }));
+  const workerTargets = nextScenes;
+  if (workerTargets.length === 0) return nextScenes;
+
+  let cursor = 0;
+  const workerCount = Math.max(1, Math.min(SCENE_FUSION_AGENT_MAX_WORKERS, workerTargets.length));
+  const workers = Array.from({ length: workerCount }, async () => {
+    while (true) {
+      const current = cursor;
+      cursor += 1;
+      if (current >= workerTargets.length) break;
+
+      const scene = workerTargets[current];
+      if (!scene) continue;
+
+      try {
+        if (!normalizeSceneFusionName(scene.targetName) && params.productName) {
+          scene.targetName = params.productName;
+        }
+
+        const styleHint = extractStyleHintFromPrompt(scene.customPrompt);
+        const generatedPrompt = await generateRandomBackgroundPromptWithAgent({
+          productImageUrl: params.productImageUrl,
+          productNameHint: params.productName,
+          styleHint,
+          userPrompt: scene.customPrompt,
+        });
+
+        if (generatedPrompt) {
+          scene.customPrompt = mergeCustomPrompt(scene.customPrompt, `场景建议：${generatedPrompt}`);
+        }
+      } catch (error) {
+        console.warn(
+          `[SceneFusion][${params.requestId}] Random scene prompt enhance skipped: scene=${scene.id}`,
+          error
+        );
+      }
+    }
+  });
+
+  await Promise.all(workers);
+  return nextScenes;
+}
+
 async function enrichSceneLabelsWithAgent(params: {
   requestId: string;
   productImageUrl: string;
@@ -1426,8 +1554,9 @@ export async function POST(request: Request) {
       );
     }
     
-    const { productImage, productName, aspectRatio, imageSize, scenes } = parseResult.data;
+    const { productImage, productName, sceneMode, aspectRatio, imageSize, scenes } = parseResult.data;
     const requestId = `sf-${Date.now()}-${Math.random().toString(36).slice(2, 8)}`;
+    const resolvedSceneMode = sceneMode || "scene-fission";
     
     // 计算输出尺寸
     const size = calculateSize(aspectRatio || "auto", imageSize || "2K");
@@ -1444,6 +1573,7 @@ export async function POST(request: Request) {
     
     console.log(`[SceneFusion] Processing ${scenes.length} scenes for user ${session.user.id}`);
     console.log(`[SceneFusion] Product name: ${productName || '(not specified)'}`);
+    console.log(`[SceneFusion] Scene mode: ${resolvedSceneMode}`);
     console.log(`[SceneFusion] Using default prompt: ${config.defaultPrompt.substring(0, 50)}...`);
     console.log(`[SceneFusion] Preferred model ID: ${config.modelId || '(none)'}`);
     
@@ -1500,11 +1630,12 @@ export async function POST(request: Request) {
     if (productImage.startsWith("data:")) {
       productImageUrl = await uploadBase64ToS3(productImage, "scene-fusion-product");
     }
+    const shouldForcePreRmbg = resolvedSceneMode === "random-bg";
     const preprocessedProduct = await preprocessProductImageWithRmbg(
       request,
       requestId,
       productImageUrl,
-      config.preRmbgEnabled
+      shouldForcePreRmbg ? true : config.preRmbgEnabled
     );
     const fusionProductImageUrl = preprocessedProduct.productImageUrl;
     console.log(
@@ -1531,7 +1662,15 @@ export async function POST(request: Request) {
       scenes: processedScenes,
     });
     const resolvedProductName = enriched.productName;
-    const resolvedScenes = enriched.scenes;
+    let resolvedScenes = enriched.scenes;
+    if (resolvedSceneMode === "random-bg") {
+      resolvedScenes = await enrichRandomBackgroundScenesWithAgent({
+        requestId,
+        productImageUrl: fusionProductImageUrl,
+        productName: resolvedProductName,
+        scenes: resolvedScenes,
+      });
+    }
     const resolvedSceneMap = new Map(resolvedScenes.map((scene) => [scene.id, scene]));
     const imageHashCache = new Map<string, string>();
 
@@ -1540,6 +1679,13 @@ export async function POST(request: Request) {
         .map((scene) => `${scene.id}:${scene.targetName || "-"}`)
         .join(", ")}`
     );
+    if (resolvedSceneMode === "random-bg") {
+      console.log(
+        `[SceneFusion][${requestId}] Random-bg prompts: ${resolvedScenes
+          .map((scene) => `${scene.id}:${(scene.customPrompt || "").slice(0, 80) || "-"}`)
+          .join(" | ")}`
+      );
+    }
 
     // 6. 创建流式响应，每完成一张图就立即发送给前端
     const stream = new ReadableStream({

components/scene-fusion-view.tsx

@@ -417,6 +417,7 @@ export function SceneFusionView({
         body: JSON.stringify({
           productImage,
           productName: productName || undefined,
+          sceneMode: mode,
           aspectRatio,
           imageSize,
           scenes: scenesPayload,
@@ -632,6 +633,7 @@ export function SceneFusionView({
       body: JSON.stringify({
         productImage: params.productImageInput,
         productName: productName || undefined,
+        sceneMode: mode,
         aspectRatio,
         imageSize,
         scenes: [