feat(frontend): unify citation logic and prevent half-finished citations

- Add SafeCitationContent as single component for citation-aware body:
  useParsedCitations + shouldShowCitationLoading; show loading until
  citations complete, then render body with createCitationMarkdownComponents.
  Supports optional remarkPlugins, rehypePlugins, isHuman, img.

- Refactor MessageListItem: assistant message body now uses
  SafeCitationContent only; remove duplicate useParsedCitations,
  shouldShowCitationLoading, createCitationMarkdownComponents and
  CitationsLoadingIndicator logic. Human messages keep plain
  AIElementMessageResponse (no citation parsing).

- Use SafeCitationContent for clarification, present-files (message-list),
  thinking steps and write_file loading (message-group), subtask result
  (subtask-card). Artifact markdown preview keeps same guard
  (shouldShowCitationLoading) with ArtifactFilePreview.

- Unify loading condition: shouldShowCitationLoading(rawContent,
  cleanContent, isLoading) is the single source of truth. Show loading when
  (isLoading && hasCitationsBlock(rawContent)) or when
  (hasCitationsBlock(rawContent) && hasUnreplacedCitationRefs(cleanContent))
  so Pro/Ultra modes also show "loading citations" and half-finished
  [cite-N] never appear.

- message-group write_file: replace hasCitationsBlock + threadIsLoading
  with shouldShowCitationLoading(fileContent, cleanContent,
  threadIsLoading && isLast) for consistency.

- citations/utils: parse incomplete <citations> during streaming;
  remove isCitationsBlockIncomplete; keep hasUnreplacedCitationRefs
  internal; document display rule in file header.

Co-authored-by: Cursor <cursoragent@cursor.com>

---
feat(前端): 统一引用逻辑并杜绝半成品引用

- 新增 SafeCitationContent 作为引用正文的唯一出口：内部使用
  useParsedCitations + shouldShowCitationLoading，在引用未就绪时只显示
  「正在整理引用」，就绪后用 createCitationMarkdownComponents 渲染正文；
  支持可选 remarkPlugins、rehypePlugins、isHuman、img。

- 重构 MessageListItem：助手消息正文仅通过 SafeCitationContent 渲染，
  删除重复的 useParsedCitations、shouldShowCitationLoading、
  createCitationMarkdownComponents、CitationsLoadingIndicator 等逻辑；
  用户消息仍用 AIElementMessageResponse，不做引用解析。

- 澄清、present-files（message-list）、思考步骤与 write_file 加载
  （message-group）、子任务结果（subtask-card）均使用
  SafeCitationContent；Artifact 的 markdown 预览仍用同一 guard
  shouldShowCitationLoading，正文由 ArtifactFilePreview 渲染。

- 统一加载条件：shouldShowCitationLoading(rawContent, cleanContent,
  isLoading) 为唯一判断。在「流式中且已有引用块」或「有引用块且
  cleanContent 中仍有未替换的 [cite-N]」时仅显示加载，从而在 Pro/Ultra
  下也能看到「正在整理引用」，且永不出现半成品 [cite-N]。

- message-group 的 write_file：用 shouldShowCitationLoading(
  fileContent, cleanContent, threadIsLoading && isLast) 替代
  hasCitationsBlock + threadIsLoading，与其他场景一致。

- citations/utils：流式时解析未闭合的 <citations>；移除
  isCitationsBlockIncomplete；hasUnreplacedCitationRefs 保持内部使用；
  在文件头注释中说明展示规则。

frontend/src/components/workspace/messages/subtask-card.tsx

@@ -18,6 +18,7 @@ import { Button } from "@/components/ui/button";
 import { ShineBorder } from "@/components/ui/shine-border";
 import { useI18n } from "@/core/i18n/hooks";
 import { hasToolCalls } from "@/core/messages/utils";
+import { useRehypeSplitWordsIntoSpans } from "@/core/rehype";
 import {
   streamdownPlugins,
   streamdownPluginsWithWordAnimation,
@@ -28,9 +29,12 @@ import { cn } from "@/lib/utils";
 
 import { FlipDisplay } from "../flip-display";
 
+import { SafeCitationContent } from "./safe-citation-content";
+
 export function SubtaskCard({
   className,
   taskId,
+  isLoading,
 }: {
   className?: string;
   taskId: string;
@@ -38,6 +42,7 @@ export function SubtaskCard({
 }) {
   const { t } = useI18n();
   const [collapsed, setCollapsed] = useState(true);
+  const rehypePlugins = useRehypeSplitWordsIntoSpans(isLoading);
   const task = useSubtask(taskId)!;
   const icon = useMemo(() => {
     if (task.status === "completed") {
@@ -147,7 +152,13 @@ export function SubtaskCard({
               ></ChainOfThoughtStep>
               <ChainOfThoughtStep
                 label={
-                  <Streamdown {...streamdownPlugins}>{task.result}</Streamdown>
+                  task.result ? (
+                    <SafeCitationContent
+                      content={task.result}
+                      isLoading={false}
+                      rehypePlugins={rehypePlugins}
+                    />
+                  ) : null
                 }
               ></ChainOfThoughtStep>
             </>