feat: add citation/reference support to deep research reports (#1143)

* feat: add citation/reference support to deep research reports (#1141)

- Enhance lead agent system prompt with mandatory citation requirements
  after web_search/web_fetch tool usage
- Add citation examples and best practices to GitHub Deep Research skill
- Add citation hints to report template (Executive Summary, Key Analysis)
- Style regular markdown links in frontend for visual distinction
  (color, underline, hover effect)
- Fix TitleMiddleware being registered when title generation is disabled

* fix: address PR review comments

- Revert TitleMiddleware conditional registration (agent.py) to avoid
  sync/async incompatibility with DeerFlowClient
- Fix markdown link rendering: merge classNames instead of overwriting,
  only set target=_blank for external http(s) URLs
- Remove unrelated package.json/pnpm-lock.yaml changes

* fix: use plain markdown links in Sources section for cleaner rendering

Inline citations in report body use [citation:Title](URL) for pill/badge style.
Sources section uses plain [Title](URL) for simple underlined link style.

* fix(frontend): render plain links as underlined text in artifact markdown

Only links with citation: prefix render as Badge pills.
Regular links in Sources section now render as underlined text links.

---------

Co-authored-by: Willem Jiang <willem.jiang@gmail.com>

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

@@ -38,7 +38,7 @@ import { checkCodeFile, getFileName } from "@/core/utils/files";
 import { env } from "@/env";
 import { cn } from "@/lib/utils";
 
-import { CitationLink } from "../citations/citation-link";
+import { ArtifactLink } from "../citations/artifact-link";
 import { useThread } from "../messages/context";
 import { Tooltip } from "../tooltip";
 
@@ -274,7 +274,7 @@ export function ArtifactFilePreview({
         <Streamdown
           className="size-full"
           {...streamdownPlugins}
-          components={{ a: CitationLink }}
+          components={{ a: ArtifactLink }}
         >
           {content ?? ""}
         </Streamdown>

frontend/src/components/workspace/citations/artifact-link.tsx

@@ -0,0 +1,33 @@
+import type { AnchorHTMLAttributes } from "react";
+
+import { cn } from "@/lib/utils";
+
+import { CitationLink } from "./citation-link";
+
+function isExternalUrl(href: string | undefined): boolean {
+  return !!href && /^https?:\/\//.test(href);
+}
+
+/** Link renderer for artifact markdown: citation: prefix → CitationLink, otherwise underlined text. */
+export function ArtifactLink(props: AnchorHTMLAttributes<HTMLAnchorElement>) {
+  if (typeof props.children === "string") {
+    const match = /^citation:(.+)$/.exec(props.children);
+    if (match) {
+      const [, text] = match;
+      return <CitationLink {...props}>{text}</CitationLink>;
+    }
+  }
+  const { className, target, rel, ...rest } = props;
+  const external = isExternalUrl(props.href);
+  return (
+    <a
+      {...rest}
+      className={cn(
+        "text-primary underline decoration-primary/30 underline-offset-2 hover:decoration-primary/60 transition-colors",
+        className,
+      )}
+      target={target ?? (external ? "_blank" : undefined)}
+      rel={rel ?? (external ? "noopener noreferrer" : undefined)}
+    />
+  );
+}

frontend/src/components/workspace/messages/markdown-content.tsx

@@ -1,16 +1,21 @@
 "use client";
 
 import { useMemo } from "react";
-import type { HTMLAttributes } from "react";
+import type { AnchorHTMLAttributes } from "react";
 
 import {
   MessageResponse,
   type MessageResponseProps,
 } from "@/components/ai-elements/message";
 import { streamdownPlugins } from "@/core/streamdown";
+import { cn } from "@/lib/utils";
 
 import { CitationLink } from "../citations/citation-link";
 
+function isExternalUrl(href: string | undefined): boolean {
+  return !!href && /^https?:\/\//.test(href);
+}
+
 export type MarkdownContentProps = {
   content: string;
   isLoading: boolean;
@@ -30,7 +35,7 @@ export function MarkdownContent({
 }: MarkdownContentProps) {
   const components = useMemo(() => {
     return {
-      a: (props: HTMLAttributes<HTMLAnchorElement>) => {
+      a: (props: AnchorHTMLAttributes<HTMLAnchorElement>) => {
         if (typeof props.children === "string") {
           const match = /^citation:(.+)$/.exec(props.children);
           if (match) {
@@ -38,7 +43,16 @@ export function MarkdownContent({
             return <CitationLink {...props}>{text}</CitationLink>;
           }
         }
-        return <a {...props} />;
+        const { className, target, rel, ...rest } = props;
+        const external = isExternalUrl(props.href);
+        return (
+          <a
+            {...rest}
+            className={cn("text-primary underline decoration-primary/30 underline-offset-2 hover:decoration-primary/60 transition-colors", className)}
+            target={target ?? (external ? "_blank" : undefined)}
+            rel={rel ?? (external ? "noopener noreferrer" : undefined)}
+          />
+        );
       },
       ...componentsFromProps,
     };