diff --git a/docs/content/docs/guides/unibox.mdx b/docs/content/docs/guides/unibox.mdx
index 8e3d1bc45..b7ae50a06 100644
--- a/docs/content/docs/guides/unibox.mdx
+++ b/docs/content/docs/guides/unibox.mdx
@@ -13,6 +13,7 @@ The columns are yours to size. Every choice here is remembered in the browser yo
 
 | Control | What it does |
 | --- | --- |
+| The divider between the scope rail and the list | Drag it to resize the scope rail. With focus, arrow keys nudge it (hold `Shift` for a bigger step), `Home` and `End` set the minimum and maximum, and `Enter` (or a double-click) restores the default 220 px. The width is remembered in this browser. |
 | The divider between the list and the thread | Drag it to widen the conversation list so long subjects fit, or to give the space back to the thread. It also takes the keyboard once it has focus: arrow keys nudge it (hold `Shift` for a bigger step), `Home` and `End` go to the narrowest and widest the window allows, `Enter` (or a double-click) puts it back to the default. |
 | **Collapse** at the bottom of the left navigation, or `b` | Shrinks Warmbly's own navigation to an icon rail and gives the width to the page. Row labels become tooltips; unread mail keeps its count badge and an open [Advisor](/guides/advisor/) finding shows as a coloured dot on the icon. The same control expands it again. |
 | The section headers in the left navigation (Email, CRM, Resources) | Click one to fold its section away, and again to bring it back. Like the other layout choices, it is remembered in this browser. A folded section still shows the page you are on, and a coloured dot beside its header flags an open [Advisor](/guides/advisor/) finding on one of the pages it hides. The icon rail follows the same choice. |
diff --git a/web/src/app/app/unibox/page.tsx b/web/src/app/app/unibox/page.tsx
index f8f743970..dc737421b 100644
--- a/web/src/app/app/unibox/page.tsx
+++ b/web/src/app/app/unibox/page.tsx
@@ -28,6 +28,9 @@ import {
   UNIBOX_LIST_DEFAULT_WIDTH,
   UNIBOX_LIST_MAX_WIDTH,
   UNIBOX_LIST_MIN_WIDTH,
+  UNIBOX_RAIL_DEFAULT_WIDTH,
+  UNIBOX_RAIL_MAX_WIDTH,
+  UNIBOX_RAIL_MIN_WIDTH,
 } from "@/stores";
 import { uniboxListMaxWidth, uniboxThreadReserve } from "@/lib/uniboxLayout";
 import { useResizablePane } from "@/hooks/useResizablePane";
@@ -66,9 +69,12 @@ export default function UniboxPage() {
   // width the column does not have.
   const listWidth = useAppStore((s) => s.uniboxListWidth);
   const setListWidth = useAppStore((s) => s.setUniboxListWidth);
+  const railWidth = useAppStore((s) => s.uniboxRailWidth);
+  const setRailWidth = useAppStore((s) => s.setUniboxRailWidth);
   const contactRailOpen = useAppStore((s) => s.uniboxContactRailOpen);
   const isWide = useMediaQuery(LG_QUERY);
   const rowRef = React.useRef<HTMLDivElement>(null);
+  const railRef = React.useRef<HTMLElement>(null);
   const listRef = React.useRef<HTMLDivElement>(null);
   const [maxWidth, setMaxWidth] = React.useState(UNIBOX_LIST_MAX_WIDTH);
 
@@ -109,8 +115,23 @@ export default function UniboxPage() {
     sync();
     const ro = new ResizeObserver(sync);
     ro.observe(row);
+    // A rail drag moves the list's left edge without resizing the row.
+    if (railRef.current) ro.observe(railRef.current);
     return () => ro.disconnect();
-  }, [measureMax]);
+  }, [measureMax, railWidth]);
+
+  const { width: renderedRailWidth, separatorProps: railSeparatorProps } = useResizablePane({
+    value: railWidth,
+    onChange: setRailWidth,
+    min: UNIBOX_RAIL_MIN_WIDTH,
+    max: UNIBOX_RAIL_MAX_WIDTH,
+    defaultValue: UNIBOX_RAIL_DEFAULT_WIDTH,
+    paneRef: railRef,
+    cssVar: "--unibox-rail-w",
+    label: "Resize the scope rail",
+    controls: "unibox-scope-rail",
+    valueText: (w) => `Scope rail ${w} pixels`,
+  });
 
   // The splitter itself: pointer capture, the body lock, the window-splitter
   // keys and the ARIA bundle all live in the shared hook, which the assistant
@@ -447,10 +468,22 @@ export default function UniboxPage() {
         />
 
         <div ref={rowRef} className="flex-1 min-h-0 flex">
-          <aside className="hidden lg:flex w-[220px] shrink-0 h-full">
+          <aside
+            ref={railRef}
+            id="unibox-scope-rail"
+            style={{ "--unibox-rail-w": `${renderedRailWidth}px` } as React.CSSProperties}
+            className="hidden lg:flex w-[var(--unibox-rail-w)] shrink-0 h-full [&>nav]:border-r-0"
+          >
             <ScopeRail scope={scope} onChange={setScope} />
           </aside>
 
+          <div
+            {...railSeparatorProps}
+            className="group hidden lg:flex w-1.5 shrink-0 cursor-col-resize items-stretch justify-center outline-none"
+          >
+            <span className="w-px bg-slate-200 transition-[background-color,width] group-hover:bg-sky-400 group-active:bg-sky-500 group-focus-visible:w-0.5 group-focus-visible:bg-sky-500" />
+          </div>
+
           {scope.kind === "scheduled" ? (
             // Scheduled scope takes the full right side — a
             // queued send has no thread context to load.
diff --git a/web/src/app/app/unibox/uniboxRailResize.test.tsx b/web/src/app/app/unibox/uniboxRailResize.test.tsx
new file mode 100644
index 000000000..76baa2553
--- /dev/null
+++ b/web/src/app/app/unibox/uniboxRailResize.test.tsx
@@ -0,0 +1,198 @@
+import React from "react";
+import { describe, it, expect, vi, beforeAll, beforeEach, afterEach } from "vitest";
+import { screen, act, fireEvent, cleanup } from "@testing-library/react";
+import { useAppStore } from "@/stores";
+import { installLayoutShims, mount, setViewportWidth, settle, SUITE } from "./uniboxHarness";
+
+beforeAll(() => {
+    installLayoutShims();
+    setViewportWidth(1512);
+});
+
+vi.mock("@/lib/api/client/Request", () => ({
+    default: async (cfg: { url?: string }) => {
+        const { route } = await import("./uniboxHarness");
+        return route(String(cfg?.url ?? ""));
+    },
+}));
+vi.mock("@/lib/helper/getToken", () => ({
+    default: () => ({
+        access_token: "a",
+        refresh_token: "r",
+        access_token_expires_at: new Date(Date.now() + 3600e3).toISOString(),
+        refresh_token_expires_at: new Date(Date.now() + 3600e3).toISOString(),
+    }),
+}));
+vi.mock("@/hooks/SocketProvider", () => ({
+    default: ({ children }: { children: React.ReactNode }) => <>{children}</>,
+}));
+vi.mock("@/hooks/context/socket", async (orig) => {
+    const actual = (await orig()) as Record<string, unknown>;
+    return {
+        ...actual,
+        useSocket: () => ({
+            isConnected: false,
+            subscribeToChannel: () => () => {},
+            pushToChannel: () => {},
+            socket: null,
+            status: "closed",
+        }),
+        useChannel: () => ({ state: "closed", push: () => {}, channel: null }),
+        useChannelEvent: () => {},
+        useChannelSubscription: () => {},
+    };
+});
+
+const separator = () => screen.getByRole("separator", { name: "Resize the scope rail" });
+const rail = () => document.getElementById("unibox-scope-rail")!;
+const railVar = () => rail().style.getPropertyValue("--unibox-rail-w");
+const originalStorage = useAppStore.persist.getOptions().storage;
+
+describe("resizable unibox scope rail", SUITE, () => {
+    beforeEach(() => {
+        useAppStore.setState({ navCollapsed: false, uniboxRailWidth: 220, uniboxListWidth: 360 });
+    });
+
+    afterEach(() => {
+        cleanup();
+        useAppStore.persist.setOptions({ storage: originalStorage });
+        vi.mocked(localStorage.getItem).mockReset();
+        vi.restoreAllMocks();
+        vi.unstubAllGlobals();
+    });
+
+    it("renders an accessible 220px separator beside the rail, hidden below lg", async () => {
+        expect(useAppStore.getInitialState().uniboxRailWidth).toBe(220);
+        await mount("/app/unibox");
+        await settle();
+        expect(separator()).toHaveAttribute("aria-valuenow", "220");
+        expect(separator()).toHaveAttribute("aria-valuemin", "180");
+        expect(separator()).toHaveAttribute("aria-valuemax", "360");
+        expect(separator()).toHaveAttribute("aria-orientation", "vertical");
+        expect(separator()).toHaveAttribute("aria-controls", "unibox-scope-rail");
+        expect(separator().previousElementSibling).toBe(rail());
+        expect(separator().nextElementSibling).toHaveAttribute("id", "unibox-conversation-list");
+        expect(separator().className).toContain("hidden lg:flex");
+        expect(rail().className).toContain("hidden lg:flex");
+        expect(railVar()).toBe("220px");
+    });
+
+    it("changes the pane and store with arrow keys and resets with Enter and double-click", async () => {
+        await mount();
+        await settle();
+        act(() => fireEvent.keyDown(separator(), { key: "ArrowRight" }));
+        expect(useAppStore.getState().uniboxRailWidth).toBe(236);
+        expect(railVar()).toBe("236px");
+        expect(separator()).toHaveAttribute("aria-valuenow", "236");
+        act(() => fireEvent.keyDown(separator(), { key: "ArrowLeft", shiftKey: true }));
+        expect(useAppStore.getState().uniboxRailWidth).toBe(188);
+        expect(railVar()).toBe("188px");
+        act(() => fireEvent.keyDown(separator(), { key: "Enter" }));
+        expect(useAppStore.getState().uniboxRailWidth).toBe(220);
+        expect(railVar()).toBe("220px");
+        act(() => fireEvent.keyDown(separator(), { key: "End" }));
+        expect(useAppStore.getState().uniboxRailWidth).toBe(360);
+        act(() => fireEvent.doubleClick(separator()));
+        expect(useAppStore.getState().uniboxRailWidth).toBe(220);
+        expect(railVar()).toBe("220px");
+    });
+
+    it("drags the pane, commits on release and stops at both bounds", async () => {
+        await mount();
+        await settle();
+        act(() => {
+            fireEvent.pointerDown(separator(), { clientX: 220, button: 0, pointerId: 1 });
+            fireEvent.pointerMove(separator(), { clientX: 300, pointerId: 1 });
+        });
+        expect(railVar()).toBe("300px");
+        expect(useAppStore.getState().uniboxRailWidth).toBe(220);
+        act(() => fireEvent.pointerUp(separator(), { pointerId: 1 }));
+        expect(useAppStore.getState().uniboxRailWidth).toBe(300);
+        act(() => {
+            fireEvent.pointerDown(separator(), { clientX: 300, button: 0, pointerId: 2 });
+            fireEvent.pointerMove(separator(), { clientX: 4000, pointerId: 2 });
+            fireEvent.pointerUp(separator(), { pointerId: 2 });
+        });
+        expect(useAppStore.getState().uniboxRailWidth).toBe(360);
+        expect(railVar()).toBe("360px");
+        act(() => {
+            fireEvent.pointerDown(separator(), { clientX: 360, button: 0, pointerId: 3 });
+            fireEvent.pointerMove(separator(), { clientX: 0, pointerId: 3 });
+            fireEvent.pointerUp(separator(), { pointerId: 3 });
+        });
+        expect(useAppStore.getState().uniboxRailWidth).toBe(180);
+        expect(railVar()).toBe("180px");
+    });
+
+    it.each([
+        [4, 180],
+        [99999, 360],
+        [null, 220],
+        ["300", 220],
+        [undefined, 220],
+    ])("rehydrates stored width %s as %s", async (stored, expected) => {
+        vi.mocked(localStorage.getItem).mockImplementation((key) => key === "warmbly-storage"
+            ? JSON.stringify({ state: { uniboxRailWidth: stored } })
+            : null);
+        await useAppStore.persist.rehydrate();
+        expect(useAppStore.getState().uniboxRailWidth).toBe(expected);
+    });
+
+    it("persists a chosen width and restores it on rehydration", async () => {
+        await mount();
+        await settle();
+        vi.mocked(localStorage.setItem).mockClear();
+        act(() => fireEvent.keyDown(separator(), { key: "ArrowRight" }));
+        const saved = vi.mocked(localStorage.setItem).mock.calls
+            .filter(([key]) => key === "warmbly-storage").at(-1)![1];
+        expect(JSON.parse(saved).state.uniboxRailWidth).toBe(236);
+        act(() => useAppStore.getState().setUniboxRailWidth(220));
+        vi.mocked(localStorage.getItem).mockImplementation((key) => key === "warmbly-storage" ? saved : null);
+        await act(async () => { await useAppStore.persist.rehydrate(); });
+        expect(useAppStore.getState().uniboxRailWidth).toBe(236);
+        expect(railVar()).toBe("236px");
+    });
+
+    it("re-measures the list cap after a rail change and during a drag", async () => {
+        let railResize: (() => void) | undefined;
+        vi.stubGlobal("ResizeObserver", class {
+            constructor(private sync: () => void) {}
+            observe(el: Element) {
+                if (el.id === "unibox-scope-rail") railResize = this.sync;
+            }
+            unobserve() {}
+            disconnect() {}
+        });
+        const originalRect = Element.prototype.getBoundingClientRect;
+        vi.spyOn(Element.prototype, "getBoundingClientRect").mockImplementation(function (this: Element) {
+            const list = document.getElementById("unibox-conversation-list");
+            if (this === list?.parentElement) return new DOMRect(0, 0, 1100, 800);
+            if (this === list) {
+                const left = parseFloat(railVar()) + 6;
+                return new DOMRect(left, 0, 620, 800);
+            }
+            return originalRect.call(this);
+        });
+        useAppStore.setState({ uniboxListWidth: 620 });
+        await mount();
+        await settle();
+        const listSeparator = () => screen.getByRole("separator", { name: "Resize the conversation list" });
+        // 1100 - (220 + 6) - 6px list handle - 360px thread reserve.
+        expect(listSeparator()).toHaveAttribute("aria-valuemax", "508");
+        act(() => fireEvent.keyDown(separator(), { key: "End" }));
+        expect(listSeparator()).toHaveAttribute("aria-valuemax", "368");
+        expect(listSeparator()).toHaveAttribute("aria-valuenow", "368");
+        act(() => fireEvent.keyDown(separator(), { key: "Enter" }));
+        expect(listSeparator()).toHaveAttribute("aria-valuemax", "508");
+        expect(railResize).toBeTypeOf("function");
+        act(() => {
+            fireEvent.pointerDown(separator(), { clientX: 220, button: 0, pointerId: 1 });
+            fireEvent.pointerMove(separator(), { clientX: 300, pointerId: 1 });
+            railResize!();
+        });
+        expect(listSeparator()).toHaveAttribute("aria-valuemax", "428");
+        expect(useAppStore.getState().uniboxRailWidth).toBe(220);
+        expect(useAppStore.getState().uniboxListWidth).toBe(620);
+        act(() => fireEvent.pointerUp(separator(), { pointerId: 1 }));
+    });
+});
diff --git a/web/src/stores/index.ts b/web/src/stores/index.ts
index 786ef8108..36617e021 100644
--- a/web/src/stores/index.ts
+++ b/web/src/stores/index.ts
@@ -19,6 +19,9 @@ export {
   UNIBOX_LIST_MIN_WIDTH,
   UNIBOX_LIST_MAX_WIDTH,
   UNIBOX_LIST_DEFAULT_WIDTH,
+  UNIBOX_RAIL_MIN_WIDTH,
+  UNIBOX_RAIL_MAX_WIDTH,
+  UNIBOX_RAIL_DEFAULT_WIDTH,
 } from './slices/uiSlice'
 export type { ShortcutSlice } from './slices/shortcutSlice'
 export type { DataSlice } from './slices/dataSlice'
diff --git a/web/src/stores/slices/uiSlice.ts b/web/src/stores/slices/uiSlice.ts
index f16687d5e..98fe87bd7 100644
--- a/web/src/stores/slices/uiSlice.ts
+++ b/web/src/stores/slices/uiSlice.ts
@@ -19,6 +19,15 @@ export interface UniboxRailFavorite {
   name?: string
 }
 
+export const UNIBOX_RAIL_MIN_WIDTH = 180
+export const UNIBOX_RAIL_MAX_WIDTH = 360
+export const UNIBOX_RAIL_DEFAULT_WIDTH = 220
+
+export const clampUniboxRailWidth = (w: unknown): number => {
+  if (typeof w !== 'number' || !Number.isFinite(w)) return UNIBOX_RAIL_DEFAULT_WIDTH
+  return Math.round(Math.min(UNIBOX_RAIL_MAX_WIDTH, Math.max(UNIBOX_RAIL_MIN_WIDTH, w)))
+}
+
 // Exported because rehydration bypasses the setter: zustand's default merge
 // writes localStorage straight into state, so the clamp has to run there too or
 // a hand-edited (or newly out-of-range) value reaches the DOM unchecked.
@@ -70,6 +79,7 @@ export interface UISlice {
   // against the thread pane; the CRM rail remembers the last explicit toggle
   // so closing it survives opening the next thread.
   uniboxListWidth: number
+  uniboxRailWidth: number
   uniboxContactRailOpen: boolean
 
   // Actions - Sidebar
@@ -103,6 +113,7 @@ export interface UISlice {
 
   // Actions - Unibox layout
   setUniboxListWidth: (width: number) => void
+  setUniboxRailWidth: (width: number) => void
   setUniboxContactRailOpen: (open: boolean) => void
 }
 
@@ -204,6 +215,7 @@ export const createUISlice: StateCreator<UISlice, [], [], UISlice> = (set, get)
 
   // Unibox layout
   uniboxListWidth: UNIBOX_LIST_DEFAULT_WIDTH,
+  uniboxRailWidth: UNIBOX_RAIL_DEFAULT_WIDTH,
   uniboxContactRailOpen: false,
 
   // Actions - Sidebar
@@ -279,6 +291,10 @@ export const createUISlice: StateCreator<UISlice, [], [], UISlice> = (set, get)
   toggleAIAssistant: () => set((state) => ({ aiAssistantOpen: !state.aiAssistantOpen })),
 
   // Actions - Unibox layout
+  setUniboxRailWidth: (width) => {
+    const uniboxRailWidth = clampUniboxRailWidth(width)
+    set((state) => (state.uniboxRailWidth === uniboxRailWidth ? state : { uniboxRailWidth }))
+  },
   setUniboxListWidth: (width) => {
     const uniboxListWidth = clampUniboxListWidth(width)
     set((state) => (state.uniboxListWidth === uniboxListWidth ? state : { uniboxListWidth }))
diff --git a/web/src/stores/useAppStore.ts b/web/src/stores/useAppStore.ts
index 29c8a2a80..18b1579a5 100644
--- a/web/src/stores/useAppStore.ts
+++ b/web/src/stores/useAppStore.ts
@@ -3,7 +3,7 @@ import { devtools, persist } from 'zustand/middleware'
 import { useShallow } from 'zustand/react/shallow'
 import { createUserSlice, type UserSlice } from './slices/userSlice'
 import { createOrganizationSlice, type OrganizationSlice } from './slices/organizationSlice'
-import { createUISlice, clampUniboxListWidth, sanitizeNavCollapsedSections, sanitizeUniboxRailFavorites, sanitizeUniboxRailHidden, sanitizeUniboxRailOrder, type UISlice } from './slices/uiSlice'
+import { createUISlice, clampUniboxListWidth, clampUniboxRailWidth, sanitizeNavCollapsedSections, sanitizeUniboxRailFavorites, sanitizeUniboxRailHidden, sanitizeUniboxRailOrder, type UISlice } from './slices/uiSlice'
 import { createShortcutSlice, type ShortcutSlice } from './slices/shortcutSlice'
 import { createDataSlice, type DataSlice } from './slices/dataSlice'
 import { createRealtimeSlice, type RealtimeSlice } from './slices/realtimeSlice'
@@ -38,8 +38,8 @@ export const useAppStore = create<AppStore>()(
       }),
       {
         name: 'warmbly-storage',
-        // Rehydration does not go through the slice setters, so re-clamp the one
-        // stored value that has bounds. Without this a value from an older build
+        // Rehydration does not go through the slice setters, so re-clamp the
+        // stored values that have bounds. Without this a value from an older build
         // (or a hand-edited one) renders as `width: NaNpx`.
         merge: (persisted, current) => {
           const p = (persisted ?? {}) as Partial<AppStore>
@@ -47,6 +47,7 @@ export const useAppStore = create<AppStore>()(
             ...current,
             ...p,
             uniboxListWidth: clampUniboxListWidth(p.uniboxListWidth),
+            uniboxRailWidth: clampUniboxRailWidth(p.uniboxRailWidth),
             navCollapsedSections: sanitizeNavCollapsedSections(p.navCollapsedSections),
             uniboxRailFolded: sanitizeNavCollapsedSections(p.uniboxRailFolded),
             uniboxRailHidden: sanitizeUniboxRailHidden(p.uniboxRailHidden),
@@ -65,8 +66,9 @@ export const useAppStore = create<AppStore>()(
           agentWidth: state.agentWidth,
           agentFloating: state.agentFloating,
           agentFloatRect: state.agentFloatRect,
-          // Unibox layout (list column width + CRM rail default)
+          // Unibox layout (pane widths + CRM rail default)
           uniboxListWidth: state.uniboxListWidth,
+          uniboxRailWidth: state.uniboxRailWidth,
           uniboxContactRailOpen: state.uniboxContactRailOpen,
           // Unibox scope rail (folds, hidden rows, row and section order, favorites)
           uniboxRailFolded: state.uniboxRailFolded,