diff --git a/web/src/index.css b/web/src/index.css
index 0ced4eeb50..39808b035b 100644
--- a/web/src/index.css
+++ b/web/src/index.css
@@ -468,7 +468,7 @@
 }
 
 /* Edge treatment is mode-specific but palette-independent. */
-html:not(.dark) .conversations-sidebar {
+html:not(.dark) .conversations-sidebar:not(.is-peek) {
   border-right: none;
   box-shadow: inset -8px 0 12px -8px rgb(0 0 0 / 5%);
 }
diff --git a/web/src/index.css.test.ts b/web/src/index.css.test.ts
index aa69585283..b38b69b970 100644
--- a/web/src/index.css.test.ts
+++ b/web/src/index.css.test.ts
@@ -196,7 +196,7 @@ describe("index.css sidebar canvas", () => {
     /:root:not\(\.dark\)\[data-theme\] \.conversations-sidebar,[^{]*\.dark\[data-theme\] \.conversations-sidebar \{[^}]*\}/,
   )?.[0];
   const lightEdgeRule = cssSource.match(
-    /html:not\(\.dark\) \.conversations-sidebar \{[^}]*\}/,
+    /html:not\(\.dark\) \.conversations-sidebar(?::not\(\.is-peek\))? \{[^}]*\}/,
   )?.[0];
   const darkEdgeRule = cssSource.match(/\.dark \.conversations-sidebar \{[^}]*\}/)?.[0];
 
diff --git a/web/src/shell/AppShell.tsx b/web/src/shell/AppShell.tsx
index 5aad6cfc20..30e4b573c3 100644
--- a/web/src/shell/AppShell.tsx
+++ b/web/src/shell/AppShell.tsx
@@ -159,6 +159,8 @@ export function AppShell() {
   const inlinePanelMinWidth = rightRailTab === "files" && fileViewerCommentsOpen ? 720 : undefined;
   const [searchParams, setSearchParams] = useSearchParams();
   const [sidebarOpen, setSidebarOpen] = useState(initialSidebarOpen);
+  const [sidebarPeek, setSidebarPeek] = useState(false);
+
   // Reads the same module-level store Sidebar drives, so the rail's ceiling
   // tracks the live sidebar width (including a drag) rather than a guess.
   const { width: sidebarWidth } = useResizableSidebar();
@@ -987,6 +989,15 @@ export function AppShell() {
     setRightPanelOpen(next);
   };
 
+  // The hotkey (⌘⌥[) and command-palette toggle for the left sidebar. A peeking
+  // sidebar counts as open, so toggling collapses it; either way peek is
+  // cleared so we never leave `sidebarOpen` and `sidebarPeek` both true (a
+  // floating-card layout the rest of the shell treats as a pushing panel).
+  const toggleLeftSidebar = () => {
+    setSidebarOpen(!(sidebarOpen || sidebarPeek));
+    setSidebarPeek(false);
+  };
+
   // Toggle the workspace rail's full-screen (maximized) state. Entering
   // collapses the left sidebar (the maximized rail wants the full width) after
   // stashing its prior open-state; exiting restores that state. The sidebar
@@ -1009,7 +1020,7 @@ export function AppShell() {
   // ⌘⌥[ / ⌘⌥] (Ctrl+Alt on Win/Linux) toggle the left and right sidebars. Bound
   // here where both panels' open-state lives.
   useSidebarToggleHotkeys({
-    onToggleLeft: () => setSidebarOpen((prev) => !prev),
+    onToggleLeft: toggleLeftSidebar,
     onToggleRight: toggleRightPanel,
   });
 
@@ -1415,8 +1426,16 @@ export function AppShell() {
             )}
             <Sidebar
               open={sidebarOpen}
+              onOpen={() => {
+                setSidebarOpen(true);
+                setSidebarPeek(false);
+              }}
+              peek={sidebarPeek}
               dragProgress={sidebarDragProgress}
-              onClose={() => setSidebarOpen(false)}
+              onClose={() => {
+                setSidebarOpen(false);
+                setSidebarPeek(false);
+              }}
               onOpenSearch={() => setCommandPaletteOpen(true)}
             />
 
@@ -1446,8 +1465,16 @@ export function AppShell() {
                 }
               >
                 <ChatHeader
-                  sidebarOpen={sidebarOpen}
-                  onOpenSidebar={() => setSidebarOpen(true)}
+                  sidebarOpen={sidebarOpen || sidebarPeek}
+                  onOpenSidebar={(peek?: boolean) => {
+                    if (peek) {
+                      setSidebarPeek(true);
+                      setSidebarOpen(false);
+                    } else {
+                      setSidebarOpen(true);
+                      setSidebarPeek(false);
+                    }
+                  }}
                   isChildSession={isChildSession}
                   parentSessionId={activeSession?.parentSessionId}
                   conversationId={conversationId}
@@ -1712,7 +1739,7 @@ export function AppShell() {
           <CommandPalette
             open={commandPaletteOpen}
             onOpenChange={setCommandPaletteOpen}
-            onToggleLeftSidebar={() => setSidebarOpen((prev) => !prev)}
+            onToggleLeftSidebar={toggleLeftSidebar}
             onToggleRightSidebar={toggleRightPanel}
           />
           {/* Transient toasts (e.g. "session archived"). Mounted once here so
diff --git a/web/src/shell/ChatHeader.tsx b/web/src/shell/ChatHeader.tsx
index 8c68ea58e5..1281b6a4bb 100644
--- a/web/src/shell/ChatHeader.tsx
+++ b/web/src/shell/ChatHeader.tsx
@@ -26,9 +26,11 @@ import { AgentInfoButton } from "@/components/AgentInfo";
 import { nativeCodingAgentForSubagentWrapper } from "@/lib/nativeCodingAgents";
 import { PresenceAvatars } from "@/components/PresenceAvatars";
 import type { Agent } from "@/hooks/useAgents";
+import { useIsMobileViewport } from "@/hooks/useIsMobileViewport";
 import { cn } from "@/lib/utils";
 import { TAB_BADGE_BASE } from "./railTabs";
 import { ViewModeToggle } from "./ViewModeToggle";
+import { useCallback, useEffect, useRef } from "react";
 
 /**
  * Gating flags + handlers for the mobile-only session-menu FAB (the
@@ -97,7 +99,7 @@ interface ChatHeaderProps {
   /** Whether the left sidebar is open (hides the open-sidebar button). */
   sidebarOpen: boolean;
   /** Open the left sidebar. */
-  onOpenSidebar: () => void;
+  onOpenSidebar: (peek?: boolean) => void;
   /** Whether the active session is a sub-agent (shows the back link). */
   isChildSession: boolean;
   /** Parent session id for the back link's destination (when a child). */
@@ -183,6 +185,26 @@ export function ChatHeader({
   onToggleRightPanel,
   mobileMenu,
 }: ChatHeaderProps) {
+  // Dwell on the toggle for 1s to peek the sidebar; leaving before then cancels
+  // the pending peek so a quick pass-over never opens it. Peek is a desktop
+  // hover affordance — on mobile the toggle just opens the full-screen overlay,
+  // so a tap's synthetic pointerenter must not trigger it.
+  const isMobile = useIsMobileViewport();
+  const peekTimer = useRef<ReturnType<typeof setTimeout> | null>(null);
+  const cancelPeek = useCallback(() => {
+    if (peekTimer.current) {
+      clearTimeout(peekTimer.current);
+      peekTimer.current = null;
+    }
+  }, []);
+  const onPeekSidebar = useCallback(() => {
+    if (isMobile) return;
+    cancelPeek();
+    peekTimer.current = setTimeout(() => {
+      onOpenSidebar(true);
+    }, 400);
+  }, [isMobile, onOpenSidebar, cancelPeek]);
+  useEffect(() => cancelPeek, [cancelPeek]);
   // A native sub-agent (a Claude Code Task, a Codex collab thread) is bound to
   // its parent's `<vendor>-native-ui` row, so its agent name is an internal
   // the server itself hides (`public_agent_name`). Name the product instead,
@@ -223,8 +245,13 @@ export function ChatHeader({
                 variant="ghost"
                 size="icon"
                 aria-label="Open sidebar"
-                onClick={onOpenSidebar}
+                onClick={() => {
+                  cancelPeek();
+                  onOpenSidebar(false);
+                }}
                 className="text-muted-foreground hover:text-foreground"
+                onPointerEnter={onPeekSidebar}
+                onPointerLeave={cancelPeek}
               >
                 <PanelLeftIcon className="size-4" />
               </Button>
diff --git a/web/src/shell/Sidebar.rowActions.test.tsx b/web/src/shell/Sidebar.rowActions.test.tsx
index ce570a7b71..850572a9b6 100644
--- a/web/src/shell/Sidebar.rowActions.test.tsx
+++ b/web/src/shell/Sidebar.rowActions.test.tsx
@@ -999,3 +999,52 @@ describe("sharing kill switch", () => {
     expect(screen.getByTestId("share-conversation")).not.toHaveAttribute("data-disabled");
   });
 });
+
+describe("peek mode row menu", () => {
+  // Peek render variant: the menu content portals OUTSIDE the <aside>, so
+  // moving the pointer from the kebab into the open menu fires the aside's
+  // onPointerLeave. The grace-period close must hold while a menu is open.
+  function renderPeek() {
+    const onClose = vi.fn();
+    const qc = new QueryClient({ defaultOptions: { queries: { retry: false } } });
+    render(
+      <QueryClientProvider client={qc}>
+        <TooltipProvider>
+          <MemoryRouter>
+            <Sidebar open={false} peek onClose={onClose} />
+          </MemoryRouter>
+        </TooltipProvider>
+      </QueryClientProvider>,
+    );
+    return { onClose };
+  }
+
+  beforeEach(() => vi.useFakeTimers({ shouldAdvanceTime: true }));
+  afterEach(() => vi.useRealTimers());
+
+  it("holds the peek open while a row's kebab menu is open", () => {
+    const { onClose } = renderPeek();
+
+    // Open the row's kebab (Radix opens on pointerdown) — its content portals
+    // outside the aside, so the pointer entering it leaves the aside.
+    fireEvent.pointerDown(screen.getByTestId("conversation-actions"), { button: 0 });
+    expect(screen.getByTestId("rename-conversation")).toBeInTheDocument();
+
+    const aside = screen.getByRole("complementary", { name: "Conversations" });
+    fireEvent.pointerLeave(aside);
+
+    // Grace period elapses, but the open menu holds the peek — no close.
+    vi.advanceTimersByTime(1000);
+    expect(onClose).not.toHaveBeenCalled();
+  });
+
+  it("closes once the menu is gone and the pointer is away", () => {
+    const { onClose } = renderPeek();
+
+    const aside = screen.getByRole("complementary", { name: "Conversations" });
+    // No menu open: a plain pointer-leave closes after the grace period.
+    fireEvent.pointerLeave(aside);
+    vi.advanceTimersByTime(1000);
+    expect(onClose).toHaveBeenCalledTimes(1);
+  });
+});
diff --git a/web/src/shell/Sidebar.tsx b/web/src/shell/Sidebar.tsx
index 1b19b32cdf..146bdc185f 100644
--- a/web/src/shell/Sidebar.tsx
+++ b/web/src/shell/Sidebar.tsx
@@ -51,6 +51,7 @@ import {
   SquarePenIcon,
   Trash2Icon,
   XIcon,
+  PanelLeftOpenIcon,
 } from "lucide-react";
 import {
   DndContext,
@@ -253,6 +254,12 @@ type SelectionScope = "sessions" | "projects";
 interface SidebarProps {
   open: boolean;
   onClose: () => void;
+  /**
+   * Pin a peeking sidebar fully open (the in-sidebar toggle shown while
+   * peeking). Optional (defaults to a no-op) so the sidebar renders standalone
+   * in tests.
+   */
+  onOpen?: () => void;
   /**
    * Live open fraction (0 = closed, 1 = open) while the iOS shell's left-edge
    * swipe is dragging the sidebar; `null` when not dragging. When set, the
@@ -268,6 +275,10 @@ interface SidebarProps {
    * Optional (defaults to a no-op) so the sidebar renders standalone in tests.
    */
   onOpenSearch?: () => void;
+  /**
+   * Whether the sidebar is peeking.
+   */
+  peek?: boolean;
 }
 
 /**
@@ -451,7 +462,14 @@ export function useMigrateLocalPinsToServer(
   }, [pinnedLoaded, filterHonored]);
 }
 
-export function Sidebar({ open, onClose, dragProgress = null, onOpenSearch }: SidebarProps) {
+export function Sidebar({
+  open,
+  onClose,
+  onOpen,
+  dragProgress = null,
+  onOpenSearch,
+  peek,
+}: SidebarProps) {
   const [selectionMode, setSelectionMode] = useState(false);
   // Which rows the current selection targets: the flat "Sessions" list, or the
   // sessions nested inside project folders. Set when selection mode is entered
@@ -646,11 +664,37 @@ export function Sidebar({ open, onClose, dragProgress = null, onOpenSearch }: Si
   // interactive even though `open` hasn't flipped yet — treat a live drag as
   // visually open so it isn't `inert`/`aria-hidden` mid-gesture.
   const dragging = dragProgress != null;
-  const effectiveOpen = open || dragging;
+  const effectiveOpen = open || dragging || peek;
+
+  // While peeking, leaving the card closes it after a short grace period;
+  // re-entering before that fires cancels the close so a wobble doesn't
+  // dismiss it.
+  const peekCloseTimer = useRef<ReturnType<typeof setTimeout> | null>(null);
+  const cancelPeekClose = useCallback(() => {
+    if (peekCloseTimer.current) {
+      clearTimeout(peekCloseTimer.current);
+      peekCloseTimer.current = null;
+    }
+  }, []);
+  useEffect(() => cancelPeekClose, [cancelPeekClose]);
 
   return (
     <aside
       aria-label="Conversations"
+      onPointerEnter={cancelPeekClose}
+      onPointerLeave={() => {
+        if (!peek) return;
+        cancelPeekClose();
+        // Defer closing if any context menu is open
+        const tryClose = () => {
+          if (document.querySelector('[role="menu"][data-state="open"]')) {
+            peekCloseTimer.current = setTimeout(tryClose, 200);
+            return;
+          }
+          onClose();
+        };
+        peekCloseTimer.current = setTimeout(tryClose, 200);
+      }}
       className={cn(
         // Base: bg + flex column. No transition — expand/collapse snaps
         // instantly (animating the width also lagged drag-to-resize).
@@ -681,8 +725,17 @@ export function Sidebar({ open, onClose, dragProgress = null, onOpenSearch }: Si
         // divider — no outer margin or rounding. Width (the user-resizable
         // variable) animates →0 to push main; when closed the border
         // collapses too so nothing lingers.
-        "md:relative md:inset-auto md:translate-x-0 md:overflow-hidden",
-        open ? "md:m-0 md:w-[var(--sidebar-width)] " : "md:m-0 md:w-0 md:border-0",
+        "md:translate-x-0 md:overflow-hidden",
+        // Normal desktop flow: relative panel that pushes main. Suppressed while
+        // peeking so its `md:inset-auto`/`md:relative` don't override the
+        // floating-card positioning below (same `md:` layer, source order wins).
+        !peek && "md:relative md:inset-auto",
+        open || peek ? "md:m-0 md:w-[var(--sidebar-width)] " : "md:m-0 md:w-0 md:border-0",
+        // Peek: float as a card 4px off the viewport edge (capped at 300px wide),
+        // ringed and shadowed, sliding+fading in from the left so it reads as an
+        // overlay rather than a push.
+        peek &&
+          "is-peek md:absolute md:inset-2 p-0 md:max-w-[400px] ring-1 ring-border rounded-xl md:shadow-xl animate-in fade-in slide-in-from-left-4 duration-200 ease-out",
       )}
       style={
         {
@@ -705,11 +758,15 @@ export function Sidebar({ open, onClose, dragProgress = null, onOpenSearch }: Si
       {/* Right-edge resize handle (desktop only), mirroring the right rail's
           left-edge handle. Hidden on mobile, where the sidebar is a
           full-screen overlay with no resize affordance; the parent's ``inert``
-          when closed also keeps it from being draggable while collapsed. */}
-      <div
-        {...resizeHandleProps}
-        className="absolute inset-y-0 right-0 z-10 hidden w-1 cursor-col-resize transition-colors hover:bg-primary/30 active:bg-primary/50 md:block"
-      />
+          when closed also keeps it from being draggable while collapsed.
+          Hidden while peeking too — the peek card is a fixed-width flyout, not
+          a resizable panel. */}
+      {!peek && (
+        <div
+          {...resizeHandleProps}
+          className="absolute inset-y-0 right-0 z-10 hidden w-1 cursor-col-resize transition-colors hover:bg-primary/30 active:bg-primary/50 md:block"
+        />
+      )}
       {inSettings ? (
         <SettingsSidebarBody onNavClick={onNavClick} />
       ) : (
@@ -768,26 +825,49 @@ export function Sidebar({ open, onClose, dragProgress = null, onOpenSearch }: Si
                 </TooltipTrigger>
                 <TooltipContent side="bottom">Settings</TooltipContent>
               </Tooltip>
-              <Tooltip>
-                <TooltipTrigger asChild>
-                  <Button
-                    type="button"
-                    variant="ghost"
-                    size="icon-xs"
-                    aria-label="Close sidebar"
-                    onClick={onClose}
-                    className="size-6 text-muted-foreground hover:text-foreground"
-                  >
-                    {/* panel-right-open while the sidebar IS open — this button
+              {!peek ? (
+                <Tooltip>
+                  <TooltipTrigger asChild>
+                    <Button
+                      type="button"
+                      variant="ghost"
+                      size="icon-xs"
+                      aria-label="Close sidebar"
+                      onClick={onClose}
+                      className="size-6 text-muted-foreground hover:text-foreground"
+                    >
+                      {/* panel-right-open while the sidebar IS open — this button
                     only renders in the open state (ChatHeader's PanelLeftIcon
                     covers the collapsed state). */}
-                    <PanelRightOpenIcon className="ui-icon" />
-                  </Button>
-                </TooltipTrigger>
-                {/* Bottom placement keeps the tooltip clear of the macOS
+                      <PanelRightOpenIcon className="ui-icon" />
+                    </Button>
+                  </TooltipTrigger>
+                  {/* Bottom placement keeps the tooltip clear of the macOS
                 Electron shell's traffic lights at the window's top edge. */}
-                <TooltipContent side="bottom">Collapse sidebar</TooltipContent>
-              </Tooltip>
+                  <TooltipContent side="bottom">Collapse sidebar</TooltipContent>
+                </Tooltip>
+              ) : (
+                <Tooltip>
+                  <TooltipTrigger asChild>
+                    <Button
+                      type="button"
+                      variant="ghost"
+                      size="icon-xs"
+                      aria-label="Open sidebar"
+                      onClick={onOpen}
+                      className="size-6 text-muted-foreground hover:text-foreground"
+                    >
+                      {/* panel-right-open while the sidebar IS open — this button
+                    only renders in the open state (ChatHeader's PanelLeftIcon
+                    covers the collapsed state). */}
+                      <PanelLeftOpenIcon className="ui-icon" />
+                    </Button>
+                  </TooltipTrigger>
+                  {/* Bottom placement keeps the tooltip clear of the macOS
+                Electron shell's traffic lights at the window's top edge. */}
+                  <TooltipContent side="bottom">Open sidebar</TooltipContent>
+                </Tooltip>
+              )}
             </div>
           </div>