diff --git a/src/web/pages/AskPage.tsx b/src/web/pages/AskPage.tsx
index 6793c98..4c52a7b 100644
--- a/src/web/pages/AskPage.tsx
+++ b/src/web/pages/AskPage.tsx
@@ -9,6 +9,11 @@ import {
 	triggerAuthReload,
 } from "../lib/api.js";
 import { APP_API_BASE } from "../lib/paths.js";
+import {
+	ASK_SIDEBAR_MAX_WIDTH,
+	ASK_SIDEBAR_MIN_WIDTH,
+	useUiPrefsStore,
+} from "../stores/ui-prefs-store.js";
 
 /**
  * Global Ask chat. Left column: thread list. Right column: messages for
@@ -33,6 +38,61 @@ export function AskPage() {
 	// thread's origin so we can gate the composer.
 	const [activeThreadOrigin, setActiveThreadOrigin] = useState<"web" | "telegram" | null>(null);
 
+	// Persisted, resizable thread sidebar. The drag handler attaches its
+	// listeners to `document` for the duration of the drag so a fast
+	// mouse movement that leaves the handle's hitbox keeps tracking.
+	const sidebarWidth = useUiPrefsStore((s) => s.askSidebarWidth);
+	const setSidebarWidth = useUiPrefsStore((s) => s.setAskSidebarWidth);
+	const onSidebarResizeStart = useCallback(
+		(event: React.MouseEvent) => {
+			event.preventDefault();
+			const startX = event.clientX;
+			const startWidth = sidebarWidth;
+			const onMove = (e: MouseEvent) => {
+				setSidebarWidth(startWidth + (e.clientX - startX));
+			};
+			const onUp = () => {
+				document.removeEventListener("mousemove", onMove);
+				document.removeEventListener("mouseup", onUp);
+				document.body.style.cursor = "";
+				document.body.style.userSelect = "";
+			};
+			document.addEventListener("mousemove", onMove);
+			document.addEventListener("mouseup", onUp);
+			// Keep the resize cursor visible across the whole window while
+			// dragging, and stop the browser from selecting text under the
+			// pointer.
+			document.body.style.cursor = "col-resize";
+			document.body.style.userSelect = "none";
+		},
+		[sidebarWidth, setSidebarWidth],
+	);
+	const onSidebarResizeKey = useCallback(
+		(event: React.KeyboardEvent) => {
+			const STEP = 16;
+			let next = sidebarWidth;
+			switch (event.key) {
+				case "ArrowLeft":
+					next = sidebarWidth - STEP;
+					break;
+				case "ArrowRight":
+					next = sidebarWidth + STEP;
+					break;
+				case "Home":
+					next = ASK_SIDEBAR_MIN_WIDTH;
+					break;
+				case "End":
+					next = ASK_SIDEBAR_MAX_WIDTH;
+					break;
+				default:
+					return;
+			}
+			event.preventDefault();
+			setSidebarWidth(next);
+		},
+		[sidebarWidth, setSidebarWidth],
+	);
+
 	const reloadThreads = useCallback(async () => {
 		try {
 			const res = await api.getAskThreads();
@@ -226,7 +286,10 @@ export function AskPage() {
 	return (
 		<div className="flex h-full min-h-0">
 			{/* Thread sidebar */}
-			<aside className="hidden md:flex w-60 flex-shrink-0 flex-col border-r border-border bg-card/30">
+			<aside
+				className="hidden md:flex flex-shrink-0 flex-col border-r border-border bg-card/30"
+				style={{ width: `${sidebarWidth}px` }}
+			>
 				<div className="p-3 border-b border-border">
 					<button
 						type="button"
@@ -283,6 +346,23 @@ export function AskPage() {
 				</div>
 			</aside>
 
+			{/* Drag handle to resize the thread sidebar. Only rendered when
+				 the sidebar itself is visible (md+). The handle is keyboard-
+				 accessible too — Left/Right arrows step the width by 16px,
+				 Home/End jump to the clamp endpoints. */}
+			<div
+				role="separator"
+				aria-label="Resize thread sidebar"
+				aria-orientation="vertical"
+				aria-valuemin={ASK_SIDEBAR_MIN_WIDTH}
+				aria-valuemax={ASK_SIDEBAR_MAX_WIDTH}
+				aria-valuenow={sidebarWidth}
+				tabIndex={0}
+				onMouseDown={onSidebarResizeStart}
+				onKeyDown={onSidebarResizeKey}
+				className="hidden md:block w-1 cursor-col-resize bg-transparent hover:bg-border focus:bg-border focus:outline-none transition-colors"
+			/>
+
 			{/* Conversation column */}
 			<div className="flex-1 flex flex-col min-w-0">
 				<div className="px-4 py-3 border-b border-border flex items-center justify-between">
diff --git a/src/web/stores/ui-prefs-store.ts b/src/web/stores/ui-prefs-store.ts
index 5e6a66d..01fa345 100644
--- a/src/web/stores/ui-prefs-store.ts
+++ b/src/web/stores/ui-prefs-store.ts
@@ -9,6 +9,10 @@ import { create } from "zustand";
 
 const STORAGE_KEY = "agentpulse.uiPrefs";
 
+export const ASK_SIDEBAR_MIN_WIDTH = 180;
+export const ASK_SIDEBAR_MAX_WIDTH = 480;
+export const ASK_SIDEBAR_DEFAULT_WIDTH = 240;
+
 interface UiPrefs {
 	/**
 	 * Tint session cards + tabs by project (last path segment of cwd).
@@ -16,10 +20,26 @@ interface UiPrefs {
 	 * dashboard, and is subtle enough not to fight the rest of the UI.
 	 */
 	projectColors: boolean;
+
+	/**
+	 * Width (px) of the thread sidebar on the /ask page. Persisted so a
+	 * resize survives reloads. Clamped to [ASK_SIDEBAR_MIN_WIDTH,
+	 * ASK_SIDEBAR_MAX_WIDTH] when read or set so a stale value can't push
+	 * the sidebar off-screen or shrink it below the "New conversation"
+	 * button's minimum legible width.
+	 */
+	askSidebarWidth: number;
+}
+
+function clampAskSidebarWidth(width: unknown): number {
+	const numeric = typeof width === "number" ? width : Number(width);
+	if (!Number.isFinite(numeric)) return ASK_SIDEBAR_DEFAULT_WIDTH;
+	return Math.min(ASK_SIDEBAR_MAX_WIDTH, Math.max(ASK_SIDEBAR_MIN_WIDTH, Math.round(numeric)));
 }
 
 const DEFAULTS: UiPrefs = {
 	projectColors: true,
+	askSidebarWidth: ASK_SIDEBAR_DEFAULT_WIDTH,
 };
 
 function load(): UiPrefs {
@@ -28,7 +48,11 @@ function load(): UiPrefs {
 		const raw = localStorage.getItem(STORAGE_KEY);
 		if (!raw) return DEFAULTS;
 		const parsed = JSON.parse(raw) as Partial<UiPrefs>;
-		return { ...DEFAULTS, ...parsed };
+		return {
+			...DEFAULTS,
+			...parsed,
+			askSidebarWidth: clampAskSidebarWidth(parsed.askSidebarWidth ?? DEFAULTS.askSidebarWidth),
+		};
 	} catch {
 		return DEFAULTS;
 	}
@@ -44,6 +68,7 @@ function save(prefs: UiPrefs): void {
 
 interface UiPrefsStore extends UiPrefs {
 	setProjectColors: (enabled: boolean) => void;
+	setAskSidebarWidth: (width: number) => void;
 }
 
 export const useUiPrefsStore = create<UiPrefsStore>((set, get) => ({
@@ -52,4 +77,9 @@ export const useUiPrefsStore = create<UiPrefsStore>((set, get) => ({
 		set({ projectColors: enabled });
 		save({ ...get(), projectColors: enabled });
 	},
+	setAskSidebarWidth(width) {
+		const clamped = clampAskSidebarWidth(width);
+		set({ askSidebarWidth: clamped });
+		save({ ...get(), askSidebarWidth: clamped });
+	},
 }));