feat(site): rewrite localhost URLs in agent chat to port-forward links (#22891)

Uses streamdown's built-in `urlTransform` prop to intercept
`http://localhost:PORT` URLs in agent chat messages and rewrite them to
port-forwarded workspace URLs.

When the agent outputs a bare URL like `http://localhost:3000` or a
markdown link like `[app](http://localhost:8080/path)`, the URL is
rewritten to the workspace's port-forward subdomain (e.g.
`https://3000--agent--workspace--user.wildcard.host`). This makes links
clickable directly from the chat without manual port-forwarding.

## How it works

The transform is built in `AgentDetail` where workspace and proxy
context are available, then threaded as an optional prop through the
component tree:

```
AgentDetail → AgentDetailView → AgentDetailTimeline → ConversationTimeline → Response → Streamdown
```

- Uses streamdown's first-class `urlTransform` API — no monkey-patching
or rehype plugins
- Reuses the existing `portForwardURL()` utility from
`utils/portForward`
- Matches the same localhost detection as the terminal page
(`localhost`, `127.0.0.1`, `0.0.0.0`)
- Preserves pathname and search params
- Gracefully degrades: when any required context is missing (no
workspace, no wildcard proxy host), URLs pass through unchanged

## What gets transformed

| Markdown input | Transformed? |
|---|---|
| `http://localhost:8080` (bare URL, auto-linked by remark-gfm) | Yes |
| `[my app](http://localhost:3000/path)` (explicit link) | Yes |
| `\`http://localhost:8080\`` (inline code) | No (correct — code spans
are literal) |
| `https://example.com` (non-localhost) | No |

site/src/components/ai-elements/response.tsx

@@ -5,11 +5,12 @@ import {
 } from "@pierre/diffs/react";
 import type { ComponentPropsWithRef, ReactNode } from "react";
 import { useMemo } from "react";
-import { type Components, Streamdown } from "streamdown";
+import { type Components, Streamdown, type UrlTransform } from "streamdown";
 import { cn } from "utils/cn";
 
 interface ResponseProps extends Omit<ComponentPropsWithRef<"div">, "children"> {
 	children: string;
+	urlTransform?: UrlTransform;
 }
 
 const fileViewerCSS =
@@ -127,6 +128,7 @@ export const Response = ({
 	className,
 	children,
 	ref,
+	urlTransform,
 	...props
 }: ResponseProps) => {
 	const theme = useTheme();
@@ -147,7 +149,11 @@ export const Response = ({
 			)}
 			{...props}
 		>
-			<Streamdown controls={false} components={components}>
+			<Streamdown
+				controls={false}
+				components={components}
+				urlTransform={urlTransform}
+			>
 				{children}
 			</Streamdown>
 		</div>

site/src/pages/AgentsPage/AgentDetail.stories.tsx

@@ -6,6 +6,7 @@ import {
 import {
 	withAuthProvider,
 	withDashboardProvider,
+	withProxyProvider,
 	withWebSocket,
 } from "testHelpers/storybook";
 import type { Meta, StoryObj } from "@storybook/react-vite";
@@ -177,7 +178,12 @@ const wrapSSE = (payload: unknown): string =>
 const meta: Meta<typeof AgentDetailLayout> = {
 	title: "pages/AgentsPage/AgentDetail",
 	component: AgentDetailLayout,
-	decorators: [withAuthProvider, withDashboardProvider, withWebSocket],
+	decorators: [
+		withAuthProvider,
+		withDashboardProvider,
+		withProxyProvider(),
+		withWebSocket,
+	],
 	parameters: {
 		layout: "fullscreen",
 		user: MockUserOwner,

site/src/pages/AgentsPage/AgentDetail.tsx

@@ -15,6 +15,7 @@ import { deploymentSSHConfig } from "api/queries/deployment";
 import { workspaceById, workspaceByIdKey } from "api/queries/workspaces";
 import type * as TypesGen from "api/typesGenerated";
 import type { ModelSelectorOption } from "components/ai-elements";
+import { useProxy } from "contexts/ProxyContext";
 import {
 	getTerminalHref,
 	getVSCodeHref,
@@ -32,7 +33,9 @@ import {
 import { useMutation, useQuery, useQueryClient } from "react-query";
 import { useNavigate, useOutletContext, useParams } from "react-router";
 import { toast } from "sonner";
+import type { UrlTransform } from "streamdown";
 import { pageTitle } from "utils/page";
+import { portForwardURL } from "utils/portForward";
 import {
 	AgentChatInput,
 	type ChatMessageInputRef,
@@ -80,6 +83,8 @@ import {
 import { useFileAttachments } from "./useFileAttachments";
 import { useGitWatcher } from "./useGitWatcher";
 
+const localHosts = new Set(["localhost", "127.0.0.1", "0.0.0.0"]);
+
 const lastModelConfigIDStorageKey = "agents.last-model-config-id";
 /** @internal Exported for testing. */
 export const draftInputStorageKeyPrefix = "agents.draft-input.";
@@ -100,6 +105,7 @@ interface AgentDetailTimelineProps {
 	) => void;
 	editingMessageId?: number | null;
 	savingMessageId?: number | null;
+	urlTransform?: UrlTransform;
 }
 
 export const AgentDetailTimeline: FC<AgentDetailTimelineProps> = ({
@@ -109,6 +115,7 @@ export const AgentDetailTimeline: FC<AgentDetailTimelineProps> = ({
 	onEditUserMessage,
 	editingMessageId,
 	savingMessageId,
+	urlTransform,
 }) => {
 	const messagesByID = useChatSelector(store, selectMessagesByID);
 	const orderedMessageIDs = useChatSelector(store, selectOrderedMessageIDs);
@@ -177,6 +184,7 @@ export const AgentDetailTimeline: FC<AgentDetailTimelineProps> = ({
 			onEditUserMessage={onEditUserMessage}
 			editingMessageId={editingMessageId}
 			savingMessageId={savingMessageId}
+			urlTransform={urlTransform}
 		/>
 	);
 };
@@ -608,6 +616,36 @@ const AgentDetail: FC = () => {
 	const sshConfigQuery = useQuery(deploymentSSHConfig());
 	const workspace = workspaceQuery.data;
 	const workspaceAgent = getWorkspaceAgent(workspace, undefined);
+	const { proxy } = useProxy();
+
+	const urlTransform = useCallback<UrlTransform>(
+		(url) => {
+			const host = proxy.preferredWildcardHostname;
+			if (!host || !workspaceAgent || !workspace) {
+				return url;
+			}
+			try {
+				const parsed = new URL(url);
+				if (!localHosts.has(parsed.hostname)) {
+					return url;
+				}
+				return portForwardURL(
+					host,
+					Number.parseInt(parsed.port, 10),
+					workspaceAgent.name,
+					workspace.name,
+					workspace.owner_name,
+					"http",
+					parsed.pathname,
+					parsed.search,
+				);
+			} catch {
+				return url;
+			}
+		},
+		[proxy.preferredWildcardHostname, workspaceAgent, workspace],
+	);
+
 	const chatData = chatQuery.data;
 	const chatRecord = chatData?.chat;
 	const isArchived = chatRecord?.archived ?? false;
@@ -1084,6 +1122,7 @@ const AgentDetail: FC = () => {
 			handleArchiveAndDeleteWorkspaceAction={
 				handleArchiveAndDeleteWorkspaceAction
 			}
+			urlTransform={urlTransform}
 			scrollContainerRef={scrollContainerRef}
 		/>
 	);

site/src/pages/AgentsPage/AgentDetail/ConversationTimeline.tsx

@@ -19,6 +19,7 @@ import {
 	useRef,
 	useState,
 } from "react";
+import type { UrlTransform } from "streamdown";
 import { cn } from "utils/cn";
 import { ImageThumbnail } from "../AgentChatInput";
 import { ImageLightbox } from "../ImageLightbox";
@@ -36,7 +37,8 @@ const ReasoningDisclosure: FC<{
 	title?: string;
 	text: string;
 	isStreaming?: boolean;
-}> = ({ id, title, text, isStreaming = false }) => {
+	urlTransform?: UrlTransform;
+}> = ({ id, title, text, isStreaming = false, urlTransform }) => {
 	const [isOpen, setIsOpen] = useState(false);
 	const hasText = text.trim().length > 0;
 	const label = title ?? "Thinking";
@@ -45,7 +47,10 @@ const ReasoningDisclosure: FC<{
 	if (!title && hasText) {
 		return (
 			<div className="w-full">
-				<Response className="text-[11px] text-content-secondary">
+				<Response
+					className="text-[11px] text-content-secondary"
+					urlTransform={urlTransform}
+				>
 					{text}
 				</Response>
 			</div>
@@ -87,7 +92,10 @@ const ReasoningDisclosure: FC<{
 			)}
 			{isOpen && hasText ? (
 				<div id={id} className="mt-1.5">
-					<Response className="text-[11px] text-content-secondary">
+					<Response
+						className="text-[11px] text-content-secondary"
+						urlTransform={urlTransform}
+					>
 						{text}
 					</Response>
 				</div>
@@ -107,6 +115,7 @@ type RenderBlockListParams = {
 	subagentTitles?: Map<string, string>;
 	subagentStatusOverrides?: Map<string, TypesGen.ChatStatus>;
 	onImageClick?: (src: string) => void;
+	urlTransform?: UrlTransform;
 };
 
 // Wrapper that runs the smooth-streaming jitter buffer on a single
@@ -115,14 +124,15 @@ type RenderBlockListParams = {
 const SmoothedResponse: FC<{
 	text: string;
 	streamKey: string;
-}> = ({ text, streamKey }) => {
+	urlTransform?: UrlTransform;
+}> = ({ text, streamKey, urlTransform }) => {
 	const { visibleText } = useSmoothStreamingText({
 		fullText: text,
 		isStreaming: true,
 		bypassSmoothing: false,
 		streamKey,
 	});
-	return <Response>{visibleText}</Response>;
+	return <Response urlTransform={urlTransform}>{visibleText}</Response>;
 };
 
 type RenderBlockListResult = {
@@ -138,6 +148,7 @@ function renderBlockList({
 	subagentTitles,
 	subagentStatusOverrides,
 	onImageClick,
+	urlTransform,
 }: RenderBlockListParams): RenderBlockListResult {
 	const renderedToolIDs = new Set<string>();
 	const elements = blocks
@@ -149,9 +160,13 @@ function renderBlockList({
 							key={`${keyPrefix}-response-${index}`}
 							text={block.text}
 							streamKey={keyPrefix}
+							urlTransform={urlTransform}
 						/>
 					) : (
-						<Response key={`${keyPrefix}-response-${index}`}>
+						<Response
+							key={`${keyPrefix}-response-${index}`}
+							urlTransform={urlTransform}
+						>
 							{block.text}
 						</Response>
 					);
@@ -163,6 +178,7 @@ function renderBlockList({
 							title={block.title}
 							text={block.text}
 							isStreaming={isStreaming}
+							urlTransform={urlTransform}
 						/>
 					);
 				case "file-reference":
@@ -267,6 +283,7 @@ const ChatMessageItem = memo<{
 	// that fades text out toward the bottom. Used by the sticky
 	// overlay to indicate truncated content.
 	fadeFromBottom?: boolean;
+	urlTransform?: UrlTransform;
 }>(
 	({
 		message,
@@ -275,6 +292,7 @@ const ChatMessageItem = memo<{
 		editingMessageId,
 		savingMessageId,
 		fadeFromBottom = false,
+		urlTransform,
 	}) => {
 		const isUser = message.role === "user";
 		const isSavingMessage = savingMessageId === message.id;
@@ -300,6 +318,7 @@ const ChatMessageItem = memo<{
 			toolByID,
 			keyPrefix: String(message.id),
 			onImageClick: setPreviewImage,
+			urlTransform,
 		});
 		const remainingTools = parsed.tools.filter(
 			(tool) => !renderedToolIDs.has(tool.id),
@@ -483,6 +502,7 @@ export const StreamingOutput = memo<{
 	subagentStatusOverrides?: Map<string, TypesGen.ChatStatus>;
 	showInitialPlaceholder?: boolean;
 	retryState?: { attempt: number; error: string } | null;
+	urlTransform?: UrlTransform;
 }>(
 	({
 		streamState,
@@ -491,6 +511,7 @@ export const StreamingOutput = memo<{
 		subagentStatusOverrides,
 		showInitialPlaceholder = false,
 		retryState,
+		urlTransform,
 	}) => {
 		const conversationItemProps = { role: "assistant" as const };
 		const toolByID = new Map(streamTools.map((tool) => [tool.id, tool]));
@@ -502,6 +523,7 @@ export const StreamingOutput = memo<{
 			isStreaming: true,
 			subagentTitles,
 			subagentStatusOverrides,
+			urlTransform,
 		});
 		const remainingTools = streamTools.filter(
 			(tool) => !renderedToolIDs.has(tool.id),
@@ -824,6 +846,7 @@ interface ConversationTimelineProps {
 	) => void;
 	editingMessageId?: number | null;
 	savingMessageId?: number | null;
+	urlTransform?: UrlTransform;
 }
 
 export const ConversationTimeline: FC<ConversationTimelineProps> = ({
@@ -842,6 +865,7 @@ export const ConversationTimeline: FC<ConversationTimelineProps> = ({
 	onEditUserMessage,
 	editingMessageId,
 	savingMessageId,
+	urlTransform,
 }) => {
 	const shouldRenderStreamInLastSection =
 		hasStreamOutput && parsedSections.length > 0;
@@ -888,6 +912,7 @@ export const ConversationTimeline: FC<ConversationTimelineProps> = ({
 											message={message}
 											parsed={parsed}
 											savingMessageId={savingMessageId}
+											urlTransform={urlTransform}
 										/>
 									),
 								)}
@@ -900,6 +925,7 @@ export const ConversationTimeline: FC<ConversationTimelineProps> = ({
 											subagentStatusOverrides={subagentStatusOverrides}
 											showInitialPlaceholder={isAwaitingFirstStreamChunk}
 											retryState={retryState}
+											urlTransform={urlTransform}
 										/>
 									)}
 							</div>
@@ -913,6 +939,7 @@ export const ConversationTimeline: FC<ConversationTimelineProps> = ({
 							subagentStatusOverrides={subagentStatusOverrides}
 							showInitialPlaceholder={isAwaitingFirstStreamChunk}
 							retryState={retryState}
+							urlTransform={urlTransform}
 						/>
 					)}
 				</div>

site/src/pages/AgentsPage/AgentDetailView.tsx

@@ -4,6 +4,7 @@ import type { ModelSelectorOption } from "components/ai-elements";
 import { Skeleton } from "components/Skeleton/Skeleton";
 import { ArchiveIcon } from "lucide-react";
 import { type FC, type RefObject, useState } from "react";
+import type { UrlTransform } from "streamdown";
 import { cn } from "utils/cn";
 import { pageTitle } from "utils/page";
 import { AgentChatInput, type ChatMessageInputRef } from "./AgentChatInput";
@@ -110,6 +111,8 @@ interface AgentDetailViewProps {
 
 	// Scroll container ref.
 	scrollContainerRef: RefObject<HTMLDivElement | null>;
+
+	urlTransform?: UrlTransform;
 }
 
 export const AgentDetailView: FC<AgentDetailViewProps> = ({
@@ -154,6 +157,7 @@ export const AgentDetailView: FC<AgentDetailViewProps> = ({
 	handleUnarchiveAgentAction,
 	handleArchiveAndDeleteWorkspaceAction,
 	scrollContainerRef,
+	urlTransform,
 }) => {
 	// Panel/sidebar UI state – purely visual, no data-fetching
 	// implications.
@@ -267,6 +271,7 @@ export const AgentDetailView: FC<AgentDetailViewProps> = ({
 							onEditUserMessage={editing.handleEditUserMessage}
 							editingMessageId={editing.editingMessageId}
 							savingMessageId={pendingEditMessageId}
+							urlTransform={urlTransform}
 						/>
 					</div>
 				</div>