fix(exams): fix composite question sub-questions not showing in preview

- Fix buildQuestion in editor-to-structure.ts: recursively detect nested
  questionBlock nodes as subQuestions (composite questions now properly
  extract child questions instead of treating them as plain text)
- Fix buildQuestionBlock in actions.ts: AI auto-mark now generates nested
  questionBlock nodes for sub-questions instead of plain paragraphs, so
  they are properly structured and detectable by the parser
- Rewrite ExamPreview component with proper layout:
  - Question header: number + type label badge + score
  - Indented question text and options
  - Composite sub-questions shown in nested block with left border
  - Image thumbnails
  - Empty state message
  - Title centered at top
  - Group titles with bottom border

src/modules/exams/actions.ts

@@ -1137,17 +1137,28 @@ const buildTiptapDocFromAiResponse = (data: unknown): unknown => {
       })
     }
 
-    // 子题(阅读理解的小题)
+    // 子题(阅读理解的小题)—— 生成为嵌套的 questionBlock,便于编辑器层级展示与解析
     const subQuestions = Array.isArray(contentNode.subQuestions)
       ? contentNode.subQuestions
       : []
     for (const sub of subQuestions) {
       if (!isRecord(sub)) continue
       const subText = typeof sub.text === "string" ? sub.text : ""
+      const subScore = typeof sub.score === "number" ? sub.score : 0
       if (subText) {
-        inner.push({
+        // 子题文本按行拆分为段落
+        const subLines = subText.split("\n").filter((l) => l.trim().length > 0)
+        const subInner =
+          subLines.length > 0
+            ? subLines.map((line) => ({
                 type: "paragraph",
-          content: [{ type: "text", text: subText }],
+                content: [{ type: "text", text: line }],
+              }))
+            : [{ type: "paragraph", content: [{ type: "text", text: " " }] }]
+        inner.push({
+          type: "questionBlock",
+          attrs: { questionId: "", type: "text", score: subScore },
+          content: subInner,
         })
       }
     }

src/modules/exams/components/exam-rich-form.tsx

@@ -329,16 +329,16 @@ function ExamPreview({ structure }: { structure: EditorDoc }) {
   ): React.ReactNode => {
     if (node.type === "group") {
       return (
-        <div key={node.id} className="mb-4">
+        <div key={node.id} className="mb-6">
           <h3
             className={cn(
-              "font-semibold text-foreground/90",
-              depth === 0 ? "text-base" : "text-sm"
+              "font-bold border-b pb-1 mb-3",
+              depth === 0 ? "text-base text-foreground" : "text-sm text-foreground/80"
             )}
           >
             {node.title || "大题"}
           </h3>
-          <div className="mt-2 space-y-2">
+          <div className="space-y-4 pl-2">
             {(node.children ?? []).map((child) => renderNode(child, depth + 1))}
           </div>
         </div>
@@ -347,39 +347,99 @@ function ExamPreview({ structure }: { structure: EditorDoc }) {
     const question = structure.questions.find((q) => q.id === node.questionId)
     if (!question) return null
     counter.value += 1
+    const qNum = counter.value
+    const isComposite = question.type === "composite"
+    const typeLabel = question.type === "single_choice" ? "单选"
+      : question.type === "multiple_choice" ? "多选"
+      : question.type === "judgment" ? "判断"
+      : question.type === "composite" ? "复合"
+      : "简答"
+
     return (
-      <div key={node.id} className="flex gap-2">
-        <span className="min-w-[28px] font-semibold text-foreground">
-          {counter.value}.
+      <div key={node.id} className="rounded border border-border/60 bg-background p-3">
+        {/* 题目头部:题号 + 题型标签 + 分值 */}
+        <div className="flex items-center gap-2 mb-2">
+          <span className="font-bold text-foreground min-w-[32px]">{qNum}.</span>
+          <span className="rounded bg-muted px-1.5 py-0.5 text-[10px] text-muted-foreground">
+            {typeLabel}
           </span>
-        <div className="flex-1 space-y-1">
-          <div className="text-foreground/90 leading-relaxed whitespace-pre-wrap">
-            {question.content.text || "未命名题目"}
-            <span className="ml-2 text-xs text-muted-foreground">
-              ({question.score}分)
+          <span className="ml-auto text-xs text-muted-foreground">
+            {question.score} 分
           </span>
         </div>
+        {/* 题干文本 */}
+        {question.content.text && (
+          <div className="mb-2 text-sm text-foreground/90 leading-relaxed whitespace-pre-wrap pl-8">
+            {question.content.text}
+          </div>
+        )}
+        {/* 选项 */}
         {question.content.options && question.content.options.length > 0 && (
-            <div className="space-y-1">
+          <div className="space-y-1.5 pl-8 mb-2">
             {question.content.options.map((opt) => (
               <div
                 key={opt.id}
                 className="text-sm text-foreground/80 flex gap-2"
               >
-                  <span className="min-w-[20px]">{opt.id}.</span>
+                <span className="font-medium min-w-[20px]">{opt.id}.</span>
                 <span>{opt.text}</span>
               </div>
             ))}
           </div>
         )}
+        {/* 复合题子题 */}
+        {isComposite && question.content.subQuestions && question.content.subQuestions.length > 0 && (
+          <div className="mt-3 ml-4 space-y-3 border-l-2 border-primary/30 pl-4">
+            {question.content.subQuestions.map((sub, idx) => (
+              <div key={sub.id} className="text-sm">
+                <div className="flex items-center gap-2 mb-1">
+                  <span className="font-medium text-foreground/80">
+                    ({idx + 1})
+                  </span>
+                  {sub.score !== undefined && (
+                    <span className="text-xs text-muted-foreground">
+                      {sub.score} 分
+                    </span>
+                  )}
                 </div>
+                <div className="text-foreground/80 whitespace-pre-wrap pl-6">
+                  {sub.text}
+                </div>
+              </div>
+            ))}
+          </div>
+        )}
+        {/* 图片 */}
+        {question.content.images && question.content.images.length > 0 && (
+          <div className="mt-2 pl-8 flex flex-wrap gap-2">
+            {question.content.images.map((img) => (
+              <img
+                key={img.fileId}
+                src={img.url}
+                alt={img.alt || ""}
+                className="max-h-32 rounded border"
+              />
+            ))}
+          </div>
+        )}
       </div>
     )
   }
 
   return (
-    <div className="space-y-3">
-      {structure.structure.map((node) => renderNode(node))}
+    <div className="space-y-4">
+      {structure.title && (
+        <h2 className="text-center text-lg font-bold border-b pb-2">
+          {structure.title}
+        </h2>
+      )}
+      {structure.structure.length === 0 ? (
+        <p className="text-center text-sm text-muted-foreground py-8">
+          暂无题目,请在左侧编辑器中添加
+        </p>
+      ) : (
+        structure.structure.map((node) => renderNode(node))
+      )}
     </div>
   )
 }

src/modules/exams/editor/editor-to-structure.ts

@@ -84,22 +84,44 @@ const buildQuestion = (qb: JSONContent): EditorQuestion => {
     : "single_choice") as RichQuestionType
   const score = typeof attrs.score === "number" ? attrs.score : 0
   const inner = qb.content ?? []
+
+  // 分离出嵌套的 questionBlock(复合题的子题)、选项列表、图片、普通文本
+  const subQuestions: Array<{ id: string; text: string; answer?: string; score?: number }> = []
+  const nonQuestionBlocks = inner.filter((n) => {
+    if (n.type === "questionBlock") {
+      const sub = buildQuestion(n)
+      const subText = sub.content.text
+      const subOptions = sub.content.options
+        ?.map((o) => `${o.id}. ${o.text}`)
+        .join("\n")
+      const fullText = [subText, subOptions].filter(Boolean).join("\n")
+      subQuestions.push({
+        id: sub.id,
+        text: fullText || "",
+        score: sub.score,
+      })
+      return false
+    }
+    return true
+  })
+
   const text = extractText({
     type: "doc",
-    content: inner.filter(
+    content: nonQuestionBlocks.filter(
       (n) =>
         n.type !== "orderedList" &&
         n.type !== "bulletList" &&
         n.type !== "image"
     ),
   })
-  const options = parseOptions(inner)
-  const blanks = collectBlanks(inner)
-  const images = collectImages(inner)
+  const options = parseOptions(nonQuestionBlocks)
+  const blanks = collectBlanks(nonQuestionBlocks)
+  const images = collectImages(nonQuestionBlocks)
   const content: RichQuestionContent = { text: text.trim() }
   if (options.length > 0) content.options = options
   if (blanks.length > 0) content.blanks = blanks
   if (images.length > 0) content.images = images
+  if (subQuestions.length > 0) content.subQuestions = subQuestions
   return { id, type, score, content }
 }