fix(frontend): citations display + refactor link/citation utils

- Citations: no underline while streaming (message links); artifact markdown external links as citation cards
- Refactor: add isExternalUrl, syntheticCitationFromLink in core/citations; shared externalLinkClass in lib/utils; simplify message-list-item and artifact-file-detail link rendering

修复引用展示并抽离链接/引用工具
- 引用：流式输出时链接不这下划线；Artifact 内 Markdown 外链以引用卡片展示
- 重构：core/citations 新增 isExternalUrl、syntheticCitationFromLink；lib/utils 共享 externalLinkClass；精简消息与 Artifact 中的链接渲染逻辑

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

frontend/src/components/workspace/artifacts/artifact-file-detail.tsx

@@ -35,15 +35,17 @@ import { useArtifactContent } from "@/core/artifacts/hooks";
 import { urlOfArtifact } from "@/core/artifacts/utils";
 import {
   buildCitationMap,
+  isExternalUrl,
   parseCitations,
   removeAllCitations,
+  syntheticCitationFromLink,
 } from "@/core/citations";
 import { useI18n } from "@/core/i18n/hooks";
 import { installSkill } from "@/core/skills/api";
 import { streamdownPlugins } from "@/core/streamdown";
 import { checkCodeFile, getFileName } from "@/core/utils/files";
 import { env } from "@/env";
-import { cn } from "@/lib/utils";
+import { cn, externalLinkClass } from "@/lib/utils";
 
 import { Tooltip } from "../tooltip";
 
@@ -309,11 +311,7 @@ export function ArtifactFilePreview({
               href,
               children,
             }: React.AnchorHTMLAttributes<HTMLAnchorElement>) => {
-              if (!href) {
-                return <span>{children}</span>;
-              }
-
-              // Only render as CitationLink badge if it's a citation (in citationMap)
+              if (!href) return <span>{children}</span>;
               const citation = citationMap.get(href);
               if (citation) {
                 return (
@@ -322,14 +320,27 @@ export function ArtifactFilePreview({
                   </CitationLink>
                 );
               }
-
-              // All other links (including project URLs) render as plain links
+              if (isExternalUrl(href)) {
+                const linkText =
+                  typeof children === "string"
+                    ? children
+                    : String(React.Children.toArray(children).join("")).trim() ||
+                      href;
+                return (
+                  <CitationLink
+                    citation={syntheticCitationFromLink(href, linkText)}
+                    href={href}
+                  >
+                    {children}
+                  </CitationLink>
+                );
+              }
               return (
                 <a
                   href={href}
                   target="_blank"
                   rel="noopener noreferrer"
-                  className="text-primary underline underline-offset-2 hover:no-underline"
+                  className={externalLinkClass}
                 >
                   {children}
                 </a>

frontend/src/components/workspace/messages/message-list-item.tsx

@@ -31,7 +31,11 @@ import {
 } from "@/core/messages/utils";
 import { useRehypeSplitWordsIntoSpans } from "@/core/rehype";
 import { humanMessagePlugins, streamdownPlugins } from "@/core/streamdown";
-import { cn } from "@/lib/utils";
+import {
+  cn,
+  externalLinkClass,
+  externalLinkClassNoUnderline,
+} from "@/lib/utils";
 
 import { CopyButton } from "../copy-button";
 
@@ -79,20 +83,23 @@ export function MessageListItem({
  * Custom link component that handles citations and external links
  * Only links in citationMap are rendered as CitationLink badges
  * Other links (project URLs, regular links) are rendered as plain links
+ * During citation loading (streaming), non-citation links are rendered without underline so they match final citation style (p3)
  */
 function MessageLink({
   href,
   children,
   citationMap,
   isHuman,
+  isLoadingCitations,
 }: React.AnchorHTMLAttributes<HTMLAnchorElement> & {
   citationMap: Map<string, Citation>;
   isHuman: boolean;
+  isLoadingCitations?: boolean;
 }) {
   if (!href) return <span>{children}</span>;
 
   const citation = citationMap.get(href);
-  
+
   // Only render as CitationLink badge if it's a citation (in citationMap) and not human message
   if (citation && !isHuman) {
     return (
@@ -102,13 +109,13 @@ function MessageLink({
     );
   }
 
-  // All other links render as plain links
+  const noUnderline = !isHuman && isLoadingCitations;
   return (
     <a
       href={href}
       target="_blank"
       rel="noopener noreferrer"
-      className="text-primary underline underline-offset-2 hover:no-underline"
+      className={noUnderline ? externalLinkClassNoUnderline : externalLinkClass}
     >
       {children}
     </a>
@@ -201,12 +208,17 @@ function MessageContent_({
   // Shared markdown components
   const markdownComponents = useMemo(() => ({
     a: (props: React.AnchorHTMLAttributes<HTMLAnchorElement>) => (
-      <MessageLink {...props} citationMap={citationMap} isHuman={isHuman} />
+      <MessageLink
+        {...props}
+        citationMap={citationMap}
+        isHuman={isHuman}
+        isLoadingCitations={isLoadingCitations}
+      />
     ),
     img: (props: React.ImgHTMLAttributes<HTMLImageElement>) => (
       <MessageImage {...props} threadId={thread_id} maxWidth={isHuman ? "full" : "90%"} />
     ),
-  }), [citationMap, thread_id, isHuman]);
+  }), [citationMap, thread_id, isHuman, isLoadingCitations]);
 
   // Render message response
   // Human messages use humanMessagePlugins (no autolink) to prevent URL bleeding into adjacent text