diff --git a/e2e/workspace-responsive.e2e.ts b/e2e/workspace-responsive.e2e.ts
new file mode 100644
index 0000000..7abd49b
--- /dev/null
+++ b/e2e/workspace-responsive.e2e.ts
@@ -0,0 +1,66 @@
+import { expect, test } from "@playwright/test"
+
+test("fits desktop notebook panels inside a 13-inch viewport", async ({
+  context,
+  page,
+}) => {
+  await context.addCookies([
+    {
+      name: "better-auth.session_token",
+      value: "playwright",
+      url: "http://localhost:3000",
+    },
+  ])
+  await page.setViewportSize({ width: 1280, height: 832 })
+  await page.goto("/e2e/citation-dedupe")
+
+  const layout = page.getByTestId("desktop-panel-layout")
+  const chatPanel = page.getByTestId("desktop-chat-panel")
+  await expect(layout).toBeVisible()
+
+  await expect
+    .poll(async () => {
+      return layout.evaluate((element) => {
+        return element.scrollWidth <= element.clientWidth
+      })
+    })
+    .toBe(true)
+
+  const measurements = await layout.evaluate((element) => {
+    return {
+      clientWidth: element.clientWidth,
+      scrollWidth: element.scrollWidth,
+    }
+  })
+  const chatBounds = await chatPanel.boundingBox()
+
+  expect(measurements.scrollWidth).toBeLessThanOrEqual(
+    measurements.clientWidth,
+  )
+  expect(chatBounds?.x).toBeGreaterThanOrEqual(0)
+  expect((chatBounds?.x ?? 0) + (chatBounds?.width ?? 0)).toBeLessThanOrEqual(
+    measurements.clientWidth,
+  )
+})
+
+test("uses the tabbed notebook layout below the desktop panel minimum", async ({
+  context,
+  page,
+}) => {
+  await context.addCookies([
+    {
+      name: "better-auth.session_token",
+      value: "playwright",
+      url: "http://localhost:3000",
+    },
+  ])
+  await page.setViewportSize({ width: 1099, height: 832 })
+  await page.goto("/e2e/citation-dedupe")
+
+  await expect(page.getByTestId("desktop-panel-layout")).toBeHidden()
+  await expect(
+    page.getByRole("tab", {
+      name: /Assistant/u,
+    }),
+  ).toBeVisible()
+})
diff --git a/src/components/chat-panel.tsx b/src/components/chat-panel.tsx
index 51eef5e..47c8c5e 100644
--- a/src/components/chat-panel.tsx
+++ b/src/components/chat-panel.tsx
@@ -94,7 +94,7 @@ export function ChatPanel({
   return (
     <section
       data-testid="chat-panel"
-      className="relative z-0 flex h-full w-full max-w-full min-w-0 flex-col overflow-hidden border-border/70 bg-muted/40 lg:border-l"
+      className="relative z-0 flex h-full w-full max-w-full min-w-0 flex-col overflow-hidden border-border/70 bg-muted/40 min-[1116px]:border-l"
     >
       <AlertDialog
         open={confirmThreadId !== null}
diff --git a/src/components/mobile-tab-bar.tsx b/src/components/mobile-tab-bar.tsx
index 7d4eb84..485d292 100644
--- a/src/components/mobile-tab-bar.tsx
+++ b/src/components/mobile-tab-bar.tsx
@@ -24,7 +24,7 @@ export function MobileTabBar({
 }: MobileTabBarProps) {
   return (
     <nav
-      className="fixed inset-x-0 bottom-0 z-50 flex h-14 shrink-0 items-center justify-around border-t border-border/70 bg-background/95 backdrop-blur-sm lg:hidden"
+      className="fixed inset-x-0 bottom-0 z-50 flex h-14 shrink-0 items-center justify-around border-t border-border/70 bg-background/95 backdrop-blur-sm min-[1116px]:hidden"
       aria-label="Panel navigation"
       role="tablist"
     >
diff --git a/src/components/workspace-desktop-panels.test.ts b/src/components/workspace-desktop-panels.test.ts
index 2026442..80e58fb 100644
--- a/src/components/workspace-desktop-panels.test.ts
+++ b/src/components/workspace-desktop-panels.test.ts
@@ -5,6 +5,22 @@ import { describe, expect, it } from "vitest";
 import { useWorkspaceDesktopPanels } from "./workspace-desktop-panels";
 
 describe("useWorkspaceDesktopPanels", () => {
+  it("fits default desktop panel widths to the rendered layout width", () => {
+    const { result } = renderHook(() => useWorkspaceDesktopPanels());
+
+    act(() => {
+      result.current.handleDesktopLayoutElementChange(createPanelElement(1280));
+    });
+
+    const totalWidth =
+      result.current.desktopPanelWidths.sources +
+      result.current.desktopPanelWidths.chunks +
+      result.current.desktopPanelWidths.chat;
+
+    expect(totalWidth).toBe(1264);
+    expect(result.current.desktopPanelWidths.chat).toBeGreaterThanOrEqual(360);
+  });
+
   it("resizes desktop panels from their rendered widths during a drag", () => {
     const { result } = renderHook(() => useWorkspaceDesktopPanels());
 
diff --git a/src/components/workspace-desktop-panels.ts b/src/components/workspace-desktop-panels.ts
index b44c945..ccc6251 100644
--- a/src/components/workspace-desktop-panels.ts
+++ b/src/components/workspace-desktop-panels.ts
@@ -1,6 +1,6 @@
 "use client";
 
-import { useRef, useState } from "react";
+import { useCallback, useEffect, useRef, useState } from "react";
 
 import { workspaceShellState } from "@/components/workspace-shell-state";
 
@@ -17,6 +17,9 @@ type DesktopPanelResizeDrag = {
 type WorkspaceDesktopPanels = {
   readonly desktopPanelWidths: DesktopPanelWidths;
   readonly minimumDesktopPanelWidth: number;
+  readonly handleDesktopLayoutElementChange: (
+    element: HTMLDivElement | null,
+  ) => void;
   readonly handleDesktopPanelElementChange: (
     panel: DesktopPanelKey,
     element: HTMLDivElement | null,
@@ -37,7 +40,8 @@ export function useWorkspaceDesktopPanels(): WorkspaceDesktopPanels {
   const [desktopPanelWidths, setDesktopPanelWidths] =
     useState<DesktopPanelWidths>({
       ...workspaceShellState.defaultDesktopPanelWidths,
-    });
+  });
+  const desktopLayoutResizeObserver = useRef<ResizeObserver | null>(null);
   const desktopPanelElements = useRef<
     Record<DesktopPanelKey, HTMLDivElement | null>
   >({
@@ -47,6 +51,42 @@ export function useWorkspaceDesktopPanels(): WorkspaceDesktopPanels {
   });
   const desktopPanelResizeDrag = useRef<DesktopPanelResizeDrag | null>(null);
 
+  const fitDesktopPanelWidthsToElement = useCallback(
+    (element: HTMLDivElement): void => {
+      const renderedWidth = element.getBoundingClientRect().width;
+      setDesktopPanelWidths(
+        workspaceShellState.fitDesktopPanelWidthsToContainer(renderedWidth),
+      );
+    },
+    [],
+  );
+
+  useEffect(() => {
+    return () => {
+      desktopLayoutResizeObserver.current?.disconnect();
+    };
+  }, []);
+
+  const handleDesktopLayoutElementChange = useCallback(
+    (element: HTMLDivElement | null): void => {
+      desktopLayoutResizeObserver.current?.disconnect();
+      desktopLayoutResizeObserver.current = null;
+
+      if (!element) return;
+
+      fitDesktopPanelWidthsToElement(element);
+
+      if (typeof ResizeObserver === "undefined") return;
+
+      const resizeObserver = new ResizeObserver(() => {
+        fitDesktopPanelWidthsToElement(element);
+      });
+      resizeObserver.observe(element);
+      desktopLayoutResizeObserver.current = resizeObserver;
+    },
+    [fitDesktopPanelWidthsToElement],
+  );
+
   function getRenderedDesktopPanelWidth(
     panel: DesktopPanelKey,
     fallbackWidth: number,
@@ -117,6 +157,7 @@ export function useWorkspaceDesktopPanels(): WorkspaceDesktopPanels {
   return {
     desktopPanelWidths,
     minimumDesktopPanelWidth: workspaceShellState.getMinimumDesktopPanelWidth(),
+    handleDesktopLayoutElementChange,
     handleDesktopPanelElementChange,
     handleDesktopPanelResize,
     handleDesktopPanelResizeEnd,
diff --git a/src/components/workspace-shell-layout.test.ts b/src/components/workspace-shell-layout.test.ts
index 14cd389..76999ed 100644
--- a/src/components/workspace-shell-layout.test.ts
+++ b/src/components/workspace-shell-layout.test.ts
@@ -48,6 +48,7 @@ describe("WorkspaceShellLayout", () => {
         onChatSend: vi.fn(),
         onCitationClick: vi.fn(),
         onCreateChatThread: vi.fn(),
+        onDesktopLayoutElementChange: vi.fn(),
         onDesktopPanelElementChange: vi.fn(),
         onDesktopPanelResize: vi.fn(),
         onDesktopPanelResizeEnd: vi.fn(),
diff --git a/src/components/workspace-shell-layout.tsx b/src/components/workspace-shell-layout.tsx
index f3d3dc4..74a5ec3 100644
--- a/src/components/workspace-shell-layout.tsx
+++ b/src/components/workspace-shell-layout.tsx
@@ -1,4 +1,4 @@
-import type { ReactElement } from "react"
+import { useCallback, type ReactElement } from "react"
 
 import { ChatPanel } from "@/components/chat-panel"
 import { ChunksPanel } from "@/components/chunks-panel"
@@ -77,6 +77,7 @@ export type WorkspaceShellLayoutProps = {
     citationId: string,
   ) => void | Promise<void>
   readonly onCreateChatThread: () => void | Promise<void>
+  readonly onDesktopLayoutElementChange: (element: HTMLDivElement | null) => void
   readonly onDesktopPanelElementChange: (
     panel: DesktopPanelKey,
     element: HTMLDivElement | null,
@@ -103,6 +104,14 @@ export type WorkspaceShellLayoutProps = {
 export function WorkspaceShellLayout(
   props: WorkspaceShellLayoutProps,
 ): ReactElement {
+  const { onDesktopLayoutElementChange } = props
+  const handleDesktopLayoutRef = useCallback(
+    (element: HTMLDivElement | null): void => {
+      onDesktopLayoutElementChange(element)
+    },
+    [onDesktopLayoutElementChange],
+  )
+
   return (
     <div className="flex h-screen w-full flex-col overflow-hidden bg-background">
       <TopNav
@@ -115,7 +124,8 @@ export function WorkspaceShellLayout(
 
       <div
         data-testid="desktop-panel-layout"
-        className="relative hidden flex-1 overflow-x-auto overflow-y-hidden lg:block"
+        ref={handleDesktopLayoutRef}
+        className="relative hidden flex-1 overflow-x-auto overflow-y-hidden min-[1116px]:block"
       >
         <div
           data-testid="desktop-resizable-panels"
@@ -242,7 +252,7 @@ export function WorkspaceShellLayout(
         id="panel-sources"
         role="tabpanel"
         aria-labelledby="tab-sources"
-        className={`lg:hidden flex-1 overflow-hidden pb-14 ${
+        className={`min-[1116px]:hidden flex-1 overflow-hidden pb-14 ${
           props.mobilePanel === "sources" ? "flex flex-col" : "hidden"
         }`}
       >
@@ -264,7 +274,7 @@ export function WorkspaceShellLayout(
         id="panel-content"
         role="tabpanel"
         aria-labelledby="tab-content"
-        className={`lg:hidden flex-1 overflow-hidden pb-14 ${
+        className={`min-[1116px]:hidden flex-1 overflow-hidden pb-14 ${
           props.mobilePanel === "content" ? "flex flex-col" : "hidden"
         }`}
       >
@@ -286,7 +296,7 @@ export function WorkspaceShellLayout(
         id="panel-chat"
         role="tabpanel"
         aria-labelledby="tab-chat"
-        className={`lg:hidden flex-1 overflow-hidden pb-14 ${
+        className={`min-[1116px]:hidden flex-1 overflow-hidden pb-14 ${
           props.mobilePanel === "chat" ? "flex flex-col" : "hidden"
         }`}
       >
@@ -325,7 +335,7 @@ export function WorkspaceShellLayout(
       />
 
       {props.chat.error && (
-        <div className="fixed bottom-18 right-4 z-50 max-w-sm rounded-lg border border-destructive/30 bg-background px-4 py-3 text-sm text-destructive shadow-lg lg:bottom-4">
+        <div className="fixed bottom-18 right-4 z-50 max-w-sm rounded-lg border border-destructive/30 bg-background px-4 py-3 text-sm text-destructive shadow-lg min-[1116px]:bottom-4">
           {props.chat.error}
         </div>
       )}
diff --git a/src/components/workspace-shell-state.test.ts b/src/components/workspace-shell-state.test.ts
index 72db37c..cb5c0a4 100644
--- a/src/components/workspace-shell-state.test.ts
+++ b/src/components/workspace-shell-state.test.ts
@@ -3,6 +3,26 @@ import { describe, expect, it } from "vitest";
 import { workspaceShellState } from "./workspace-shell-state";
 
 describe("workspaceShellState", () => {
+  it("fits default desktop panel widths inside a 13-inch viewport", () => {
+    const widths = workspaceShellState.fitDesktopPanelWidthsToContainer(1280);
+    const totalWidth =
+      widths.sources +
+      widths.chunks +
+      widths.chat +
+      workspaceShellState.desktopPanelGutterWidth * 2;
+
+    expect(totalWidth).toBeLessThanOrEqual(1280);
+    expect(widths.sources).toBeGreaterThanOrEqual(
+      workspaceShellState.minimumDesktopPanelWidths.sources,
+    );
+    expect(widths.chunks).toBeGreaterThanOrEqual(
+      workspaceShellState.minimumDesktopPanelWidths.chunks,
+    );
+    expect(widths.chat).toBeGreaterThanOrEqual(
+      workspaceShellState.minimumDesktopPanelWidths.chat,
+    );
+  });
+
   it("resizes neighboring desktop panels while preserving their combined width", () => {
     const resized = workspaceShellState.resizeDesktopPanelWidths(
       {
diff --git a/src/components/workspace-shell-state.ts b/src/components/workspace-shell-state.ts
index 90fb3a8..ed6bf93 100644
--- a/src/components/workspace-shell-state.ts
+++ b/src/components/workspace-shell-state.ts
@@ -16,6 +16,8 @@ type DesktopPanelKey = keyof typeof minimumDesktopPanelWidths
 
 type DesktopPanelWidths = Record<DesktopPanelKey, number>
 
+const desktopPanelKeys = ["sources", "chunks", "chat"] as const
+
 type DesktopPanelResizeInput = {
   readonly leftPanel: DesktopPanelKey
   readonly rightPanel: DesktopPanelKey
@@ -29,6 +31,9 @@ type WorkspaceShellStateModule = {
   readonly minimumDesktopPanelWidths: typeof minimumDesktopPanelWidths
   readonly defaultDesktopPanelWidths: typeof defaultDesktopPanelWidths
   readonly getMinimumDesktopPanelWidth: () => number
+  readonly fitDesktopPanelWidthsToContainer: (
+    containerWidth: number,
+  ) => DesktopPanelWidths
   readonly resizeDesktopPanelWidths: (
     currentWidths: Readonly<DesktopPanelWidths>,
     resize: DesktopPanelResizeInput,
@@ -44,6 +49,65 @@ function getMinimumDesktopPanelWidth(): number {
   )
 }
 
+function getDefaultDesktopPanelContentWidth(): number {
+  return (
+    defaultDesktopPanelWidths.sources +
+    defaultDesktopPanelWidths.chunks +
+    defaultDesktopPanelWidths.chat
+  )
+}
+
+function getMinimumDesktopPanelContentWidth(): number {
+  return (
+    minimumDesktopPanelWidths.sources +
+    minimumDesktopPanelWidths.chunks +
+    minimumDesktopPanelWidths.chat
+  )
+}
+
+function fitDesktopPanelWidthsToContainer(
+  containerWidth: number,
+): DesktopPanelWidths {
+  if (!Number.isFinite(containerWidth) || containerWidth <= 0) {
+    return { ...defaultDesktopPanelWidths }
+  }
+
+  const availableContentWidth = containerWidth - desktopPanelGutterWidth * 2
+  const defaultContentWidth = getDefaultDesktopPanelContentWidth()
+  if (availableContentWidth >= defaultContentWidth) {
+    return { ...defaultDesktopPanelWidths }
+  }
+
+  const minimumContentWidth = getMinimumDesktopPanelContentWidth()
+  if (availableContentWidth <= minimumContentWidth) {
+    return { ...minimumDesktopPanelWidths }
+  }
+
+  const defaultExtraWidth = defaultContentWidth - minimumContentWidth
+  const availableExtraWidth = availableContentWidth - minimumContentWidth
+  const fittedWidths = {} as DesktopPanelWidths
+  let assignedWidth = 0
+
+  for (const [index, panel] of desktopPanelKeys.entries()) {
+    const isLastPanel = index === desktopPanelKeys.length - 1
+    if (isLastPanel) {
+      fittedWidths[panel] = availableContentWidth - assignedWidth
+      break
+    }
+
+    const panelExtraWidth =
+      defaultDesktopPanelWidths[panel] - minimumDesktopPanelWidths[panel]
+    const fittedWidth = Math.round(
+      minimumDesktopPanelWidths[panel] +
+        (panelExtraWidth / defaultExtraWidth) * availableExtraWidth,
+    )
+    fittedWidths[panel] = fittedWidth
+    assignedWidth += fittedWidth
+  }
+
+  return fittedWidths
+}
+
 function resizeDesktopPanelWidths(
   currentWidths: Readonly<DesktopPanelWidths>,
   resize: DesktopPanelResizeInput,
@@ -73,5 +137,6 @@ export const workspaceShellState: WorkspaceShellStateModule = {
   minimumDesktopPanelWidths,
   defaultDesktopPanelWidths,
   getMinimumDesktopPanelWidth,
+  fitDesktopPanelWidthsToContainer,
   resizeDesktopPanelWidths,
 }
diff --git a/src/components/workspace-shell.tsx b/src/components/workspace-shell.tsx
index 4e2af57..e931cf6 100644
--- a/src/components/workspace-shell.tsx
+++ b/src/components/workspace-shell.tsx
@@ -100,6 +100,7 @@ function WorkspaceShellContent({
   const {
     desktopPanelWidths,
     minimumDesktopPanelWidth,
+    handleDesktopLayoutElementChange,
     handleDesktopPanelElementChange,
     handleDesktopPanelResize,
     handleDesktopPanelResizeEnd,
@@ -150,6 +151,7 @@ function WorkspaceShellContent({
       onChatSend={chatWorkflow.handleChatSend}
       onCitationClick={citationFocus.handleCitationClick}
       onCreateChatThread={chatWorkflow.handleCreateChatThread}
+      onDesktopLayoutElementChange={handleDesktopLayoutElementChange}
       onDesktopPanelElementChange={handleDesktopPanelElementChange}
       onDesktopPanelResize={handleDesktopPanelResize}
       onDesktopPanelResizeEnd={handleDesktopPanelResizeEnd}