fix: harden prompt optimizer json parsing

lib/ai/prompt-optimizer.ts

@@ -299,6 +299,30 @@ const IMAGE_GEN_OPTIMIZER_SYSTEM_PROMPT = `你是一个专业的图片生成提
    - 细节：一句话补充风格/材质/光线/构图
 `;
 
+function parseOptimizerJsonCandidate(raw: string): {
+  optimizedPrompt?: string;
+  negativePrompt?: string;
+  suggestedParams?: {
+    aspectRatio?: string;
+    imageSize?: string;
+    imageCount?: number;
+    promptExtend?: boolean;
+  };
+} | null {
+  const normalized = raw
+    .trim()
+    .replace(/\uFEFF/g, "")
+    .replace(/[“”]/g, "\"")
+    .replace(/[‘’]/g, "'")
+    .replace(/,\s*([}\]])/g, "$1");
+  if (!normalized) return null;
+  try {
+    return JSON.parse(normalized);
+  } catch {
+    return null;
+  }
+}
+
 function parseOptimizerJson(responseText: string): {
   optimizedPrompt?: string;
   negativePrompt?: string;
@@ -309,13 +333,40 @@ function parseOptimizerJson(responseText: string): {
     promptExtend?: boolean;
   };
 } | null {
-  const jsonMatch = responseText.match(/\{[\s\S]*\}/);
-  if (!jsonMatch) return null;
-  try {
-    return JSON.parse(jsonMatch[0]);
-  } catch (error) {
-    return null;
+  if (!responseText || typeof responseText !== "string") return null;
+
+  const fencedBlocks = Array.from(
+    responseText.matchAll(/```(?:json)?\s*([\s\S]*?)```/gi)
+  ).map((match) => match[1]?.trim() || "");
+
+  for (const block of fencedBlocks) {
+    const parsed = parseOptimizerJsonCandidate(block);
+    if (parsed) return parsed;
   }
+
+  const text = responseText.trim();
+  const starts: number[] = [];
+  for (let i = 0; i < text.length; i++) {
+    if (text[i] === "{") starts.push(i);
+  }
+
+  for (const start of starts) {
+    let depth = 0;
+    for (let end = start; end < text.length; end++) {
+      if (text[end] === "{") depth += 1;
+      if (text[end] === "}") {
+        depth -= 1;
+        if (depth === 0) {
+          const candidate = text.slice(start, end + 1);
+          const parsed = parseOptimizerJsonCandidate(candidate);
+          if (parsed) return parsed;
+          break;
+        }
+      }
+    }
+  }
+
+  return null;
 }
 
 function sanitizeSuggestedParams(input?: {
@@ -590,7 +641,10 @@ export async function optimizePromptWithLLM(params: {
     }
 
     // 解析失败，回退到模板优化
-    console.log("[Prompt Optimizer LLM] Parse failed, falling back to template");
+    console.log(
+      "[Prompt Optimizer LLM] Parse failed, falling back to template. raw=",
+      responseText.slice(0, 320)
+    );
     return optimizePrompt({ originalPrompt, intent, subIntent });
 
   } catch (error) {