coder · DanielleMaywood · Aug 5, 2026 · Aug 5, 2026 · Aug 5, 2026 · Aug 5, 2026
@@ -1,6 +1,7 @@
 import type { Meta, StoryObj } from "@storybook/react-vite";
 import type { FC } from "react";
 import { useRef } from "react";
+import { hashKey } from "react-query";
 import { Outlet, useNavigate } from "react-router";
 import { expect, spyOn, userEvent, waitFor, within } from "storybook/test";
 import {
@@ -22,6 +23,7 @@ import {
 import { workspaceByIdKey } from "#/api/queries/workspaces";
 import type * as TypesGen from "#/api/typesGenerated";
 import {
+	MockChat,
 	MockChatMessage,
 	MockChatQueuedMessage,
 } from "#/testHelpers/chatEntities";
@@ -32,6 +34,7 @@ import {
 	MockOrganizationMember2,
 	MockUserOwner,
 	MockWorkspace,
+	mockApiError,
 } from "#/testHelpers/entities";
 import {
 	withAuthProvider,
@@ -3059,6 +3062,124 @@ export const SendResponseAfterChatSwitch: Story = {
 	},
 };
 
+const mockErrorChat: TypesGen.Chat = {
+	...MockChat,
+	id: CHAT_ID,
+	...baseChatFields,
+	title: "Failing chat",
+};
+
+const mockServerError = {
+	...mockApiError({ message: "Internal server error." }),
+	status: 500,
+};
+
+const withoutQuery = (
+	queries: ReturnType<typeof buildQueries>,
+	queryKey: readonly unknown[],
+) => queries.filter(({ key }) => hashKey(key) !== hashKey(queryKey));
+
+export const DetailQueryError: Story = {
+	parameters: {
+		queries: withoutQuery(
+			buildQueries(mockErrorChat, {
+				messages: [],
+				queued_messages: [],
+				has_more: false,
+			}),
+			chatKey(CHAT_ID),
+		),
+	},
+	beforeEach: () => {
+		spyOn(API.experimental, "getChat").mockRejectedValue(mockServerError);
+	},
+	play: async ({ canvasElement }) => {
+		const canvas = within(canvasElement);
+		expect(await canvas.findByText("Failed to load chat")).toBeVisible();
+		expect(canvas.queryByText("Chat not found")).not.toBeInTheDocument();
+		expect(
+			canvas.getByRole("button", { name: "Try again" }),
+		).toBeInTheDocument();
+	},
+};
+
+export const InitialMessagesError: Story = {
+	parameters: {
+		queries: withoutQuery(
+			buildQueries(mockErrorChat, {
+				messages: [],
+				queued_messages: [],
+				has_more: false,
+			}),
+			chatMessagesKey(CHAT_ID),
+		),
+	},
+	beforeEach: () => {
+		spyOn(API.experimental, "getChatMessages").mockRejectedValue(
+			mockServerError,
+		);
+	},
+	play: async ({ canvasElement }) => {
+		const canvas = within(canvasElement);
+		expect(await canvas.findByText("Failed to load chat")).toBeVisible();
+		expect(canvas.queryByText("Chat not found")).not.toBeInTheDocument();
+	},
+};
+
+export const ErrorRetryRecovers: Story = {
+	parameters: {
+		queries: withoutQuery(
+			buildQueries(mockErrorChat, {
+				messages: [],
+				queued_messages: [],
+				has_more: false,
+			}),
+			chatKey(CHAT_ID),
+		),
+	},
+	beforeEach: ({ parameters }) => {
+		const getChatSpy = spyOn(API.experimental, "getChat")
+			.mockRejectedValueOnce(mockServerError)
+			.mockResolvedValue(mockErrorChat);
+		parameters.getChatCallsForChat = () =>
+			getChatSpy.mock.calls.filter(([chatId]) => chatId === CHAT_ID).length;
+	},
+	play: async ({ canvasElement, parameters }) => {
+		const canvas = within(canvasElement);
+		expect(await canvas.findByText("Failed to load chat")).toBeVisible();
+		await userEvent.click(canvas.getByRole("button", { name: "Try again" }));
+		await waitFor(() => {
+			expect(canvas.queryByText("Failed to load chat")).not.toBeInTheDocument();
+		});
+		expect(canvas.queryByText("Chat not found")).not.toBeInTheDocument();
+		expect(parameters.getChatCallsForChat()).toBeGreaterThanOrEqual(2);
+	},
+};
+
+export const ChatNotFound: Story = {
+	parameters: {
+		queries: withoutQuery(
+			buildQueries(mockErrorChat, {
+				messages: [],
+				queued_messages: [],
+				has_more: false,
+			}),
+			chatKey(CHAT_ID),
+		),
+	},
+	beforeEach: () => {
+		spyOn(API.experimental, "getChat").mockRejectedValue({
+			...mockApiError({ message: "Chat not found." }),
+			status: 404,
+		});
+	},
+	play: async ({ canvasElement }) => {
+		const canvas = within(canvasElement);
+		expect(await canvas.findByText("Chat not found")).toBeVisible();
+		expect(canvas.queryByText("Failed to load chat")).not.toBeInTheDocument();
+	},
+};
+
 export const SendRejectedByHookDispatchFailure: Story = {
 	parameters: {
 		queries: buildQueries(

@@ -22,7 +22,7 @@ import {
 	type CreateChatMessageRequestWithClearablePlanMode,
 	watchWorkspace,
 } from "#/api/api";
-import { getErrorMessage, isApiError } from "#/api/errors";
+import { getErrorMessage, getErrorStatus, isApiError } from "#/api/errors";
 import { checkAuthorization } from "#/api/queries/authCheck";
 import { buildOptimisticEditedMessage } from "#/api/queries/chatMessageEdits";
 import {
@@ -68,6 +68,7 @@ import { isMobileViewport } from "#/utils/mobile";
 import { pageTitle } from "#/utils/page";
 import { rewriteLocalhostURL } from "#/utils/portForward";
 import { createReconnectingWebSocket } from "#/utils/reconnectingWebSocket";
+import { AgentChatPageErrorView } from "./AgentChatPageErrorView";
 import {
 	AgentChatPageLoadingView,
 	AgentChatPageNotFoundView,
@@ -1881,6 +1882,37 @@ const AgentChatPage: FC = () => {
 		);
 	}
 
+	if (chatQuery.isLoadingError || chatMessagesQuery.isLoadingError) {
+		if (getErrorStatus(chatQuery.error) === 404) {
+			return (
+				<AgentChatPageNotFoundView
+					titleElement={titleElement}
+					isSidebarCollapsed={isSidebarCollapsed}
+					onToggleSidebarCollapsed={onToggleSidebarCollapsed}
+				/>
+			);
+		}
+
+		return (
+			<AgentChatPageErrorView
+				titleElement={titleElement}
+				isSidebarCollapsed={isSidebarCollapsed}
+				onToggleSidebarCollapsed={onToggleSidebarCollapsed}
+				error={
+					chatQuery.isLoadingError ? chatQuery.error : chatMessagesQuery.error
+				}
+				onRetry={() => {
+					if (chatQuery.isLoadingError) {
+						void chatQuery.refetch();
+					}
+					if (chatMessagesQuery.isLoadingError) {
+						void chatMessagesQuery.refetch();
+					}
+				}}
+			/>
+		);
+	}
+
 	if (!chatQuery.data || !chatMessagesQuery.data?.pages?.length || !agentId) {
 		return (
 			<AgentChatPageNotFoundView

@@ -0,0 +1,60 @@
+import { RotateCcwIcon } from "lucide-react";
+import type { FC, ReactNode } from "react";
+import { getErrorDetail, getErrorMessage } from "#/api/errors";
+import { Button } from "#/components/Button/Button";
+import { ChatTopBar } from "./components/ChatTopBar";
+
+interface AgentChatPageErrorViewProps {
+	titleElement: ReactNode;
+	isSidebarCollapsed: boolean;
+	onToggleSidebarCollapsed: () => void;
+	error: unknown;
+	onRetry: () => void;
+}
+
+export const AgentChatPageErrorView: FC<AgentChatPageErrorViewProps> = ({
+	titleElement,
+	isSidebarCollapsed,
+	onToggleSidebarCollapsed,
+	error,
+	onRetry,
+}) => {
+	const detail = getErrorDetail(error);
+
+	return (
+		<div className="flex h-full min-h-0 min-w-0 flex-1 flex-col">
+			{titleElement}
+			<ChatTopBar
+				panel={{
+					showSidebarPanel: false,
+					onToggleSidebar: () => {},
+				}}
+				onArchiveAgent={() => {}}
+				onUnarchiveAgent={() => {}}
+				onArchiveAndDeleteWorkspace={() => {}}
+				hasWorkspace={false}
+				isSidebarCollapsed={isSidebarCollapsed}
+				onToggleSidebarCollapsed={onToggleSidebarCollapsed}
+			/>
+			<div className="flex flex-1 items-center justify-center px-6 text-center">
+				<div className="flex flex-col items-center">
+					<h3 className="m-0 font-medium text-base text-content-primary">
+						Failed to load chat
+					</h3>
+					<p className="m-0 mt-1 max-w-md text-sm text-content-secondary">
+						{getErrorMessage(error, "The chat could not be loaded.")}
+					</p>
+					{detail && (
+						<p className="m-0 mt-1 max-w-md text-sm text-content-secondary">
+							{detail}
+						</p>
+					)}
+					<Button size="sm" onClick={onRetry} className="mt-4">
+						<RotateCcwIcon />
+						Try again
+					</Button>
+				</div>
+			</div>
+		</div>
+	);
+};