R6: responsive — mobile rail drawer + full-screen Computer overlay

- SlidePanel gains an  prop: at ≤md the open Computer panel
  becomes a fixed full-screen layer (max-md:!w-full beats the inline
  width) instead of a cramped docked rail — the measured mobile/tablet
  behavior. The screen card goes full-bleed (no radius/shadow/max-width)
  on small screens; desktop docking is unchanged.
- LeftRail collapses behind a hamburger at ≤md and slides in as a drawer
  over the content with a backdrop, auto-closing on navigation
  (render-phase route check, no effect). Desktop keeps the static 176px
  rail (the hamburger and drawer transforms are max-md-scoped, so the
  1440 desktop suite is untouched).

83 unit tests; desktop p0/p3/a11y journeys green; verified at 390px the
rail collapses to the toggle.

Co-Authored-By: Claude Fable 5 <[email protected]>

frontend/src/components/computer/DevicePanel.tsx

@@ -41,15 +41,15 @@ export function DevicePanel({ agent }: { agent: Agent }) {
   }
 
   return (
-    <SlidePanel open={open} width={WIDTHS[device]} label="Computer">
+    <SlidePanel open={open} width={WIDTHS[device]} label="Computer" overlay>
       <div
         data-testid="device-panel-theme"
-        className="flex h-full flex-col px-3 pt-[88px] pb-6"
+        className="flex h-full flex-col px-3 pt-[88px] pb-6 max-md:bg-background max-md:p-0"
         style={clawThemeStyle(agent)}
       >
         <div
           ref={cardRef}
-          className="relative mx-auto flex h-full w-full max-w-[400px] flex-col overflow-hidden rounded-[32px] shadow-screen"
+          className="relative mx-auto flex h-full w-full max-w-[400px] flex-col overflow-hidden rounded-[32px] shadow-screen max-md:max-w-none max-md:rounded-none max-md:shadow-none"
         >
           <WallpaperSurface>
             <header className="relative flex h-11 shrink-0 items-center gap-2 px-3">

frontend/src/components/shell/LeftRail.tsx

@@ -1,8 +1,12 @@
+"use client";
+
 import Link from "next/link";
-import { Plus } from "lucide-react";
+import { usePathname } from "next/navigation";
+import { Menu, Plus, X } from "lucide-react";
+import { useRef, useState } from "react";
 
 import type { Agent, User } from "@/lib/api/schemas";
-import { AgentRosterItem } from "./AgentRosterItem";
+import { RosterList } from "./RosterList";
 import { ShellNav } from "./ShellNav";
 import { UserMenu } from "./UserMenu";
 
@@ -13,25 +17,59 @@ interface LeftRailProps {
 }
 
 /** The persistent 176px left rail (measured): wordmark, the claw avatar
- *  stack (48px squircles), dashed add tile, then global nav + the current
+ *  stack, dashed add tile, global nav + user. At ≤md it collapses behind
- *  user pinned to the bottom. */
+ *  a hamburger and slides in as a drawer over the content. */
 export function LeftRail({ user, roster, creditsBalance }: LeftRailProps) {
+  const [open, setOpen] = useState(false);
+  const pathname = usePathname();
+  // Close the drawer when the route changes (render-phase, no effect).
+  const lastPath = useRef(pathname);
+  if (lastPath.current !== pathname) {
+    lastPath.current = pathname;
+    if (open) setOpen(false);
+  }
+
   return (
-    <aside className="flex h-dvh w-rail shrink-0 flex-col px-1 py-4">
+    <>
-      <p className="px-3 pb-4 font-mono text-sm font-semibold tracking-tight text-foreground">
+      <button
+        type="button"
+        aria-label="Open navigation"
+        onClick={() => setOpen(true)}
+        className="fixed top-4 left-3 z-30 hidden size-9 items-center justify-center rounded-radius-button bg-surface-warm text-foreground shadow-card max-md:inline-flex"
+      >
+        <Menu aria-hidden size={18} />
+      </button>
+      {open && (
+        <button
+          type="button"
+          aria-label="Close navigation"
+          onClick={() => setOpen(false)}
+          className="fixed inset-0 z-40 hidden bg-black/50 max-md:block"
+        />
+      )}
+      <aside
+        className={`z-50 flex h-dvh w-rail shrink-0 flex-col px-1 py-4 transition-transform duration-normal ease-app max-md:fixed max-md:bg-background max-md:shadow-edge ${
+          open ? "max-md:translate-x-0" : "max-md:-translate-x-full"
+        }`}
+      >
+        <div className="flex items-center justify-between px-3 pb-4">
+          <p className="font-mono text-sm font-semibold tracking-tight text-foreground">
             clawmates
           </p>
+          <button
+            type="button"
+            aria-label="Close navigation"
+            onClick={() => setOpen(false)}
+            className="hidden text-muted-foreground max-md:inline-flex"
+          >
+            <X aria-hidden size={16} />
+          </button>
+        </div>
         <div className="flex-1 overflow-y-auto">
           {roster.length === 0 ? (
             <p className="px-3 text-xs text-muted-foreground">No claws yet</p>
           ) : (
-          <ul aria-label="Your claws" className="flex flex-col">
+            <RosterList roster={roster} />
-            {roster.map((agent) => (
-              <li key={agent.id}>
-                <AgentRosterItem agent={agent} />
-              </li>
-            ))}
-          </ul>
           )}
           <Link
             href="/claws/new"
@@ -53,5 +91,6 @@ export function LeftRail({ user, roster, creditsBalance }: LeftRailProps) {
           <UserMenu user={user} />
         </div>
       </aside>
+    </>
   );
 }

frontend/src/components/ui/SlidePanel.tsx

@@ -9,6 +9,9 @@ interface SlidePanelProps {
   /** Accessible name for the complementary region. */
   label: string;
   className?: string;
+  /** On ≤md screens, cover the viewport instead of docking as a rail
+   *  (the measured responsive behavior for the Computer panel). */
+  overlay?: boolean;
   children: ReactNode;
 }
 
@@ -18,12 +21,17 @@ interface SlidePanelProps {
  * pushes layout instead of overlaying it, while the inner div keeps the final
  * width so children never reflow mid-animation. Content stays mounted during
  * the exit transition and unmounts on `transitionend`.
+ *
+ * With `overlay`, at ≤md the open panel becomes a fixed full-screen layer
+ * (`!w-full` beats the inline width) so phones/tablets get the spec's
+ * full-screen Computer instead of a cramped rail.
  */
 export function SlidePanel({
   open,
   width,
   label,
   className,
+  overlay = false,
   children,
 }: SlidePanelProps) {
   const [mounted, setMounted] = useState(open);
@@ -35,21 +43,31 @@ export function SlidePanel({
   }
 
   function handleTransitionEnd(event: TransitionEvent<HTMLDivElement>) {
-    if (event.propertyName === "width" && !open && event.target === event.currentTarget) {
+    if (
+      event.propertyName === "width" &&
+      !open &&
+      event.target === event.currentTarget
+    ) {
       setMounted(false);
     }
   }
 
+  const overlayTrack =
+    overlay && open
+      ? " max-md:fixed max-md:inset-0 max-md:z-40 max-md:h-dvh max-md:!w-full"
+      : "";
+  const overlayInner = overlay ? " max-md:!w-full" : "";
+
   return (
     <div
       role="complementary"
       aria-label={label}
       aria-hidden={!open}
-      className={`panel-track ${className ?? ""}`}
+      className={`panel-track${overlayTrack} ${className ?? ""}`}
       style={{ width: open ? `${width}px` : "0px" }}
       onTransitionEnd={handleTransitionEnd}
     >
-      <div style={{ width: `${width}px` }} className="h-full">
+      <div style={{ width: `${width}px` }} className={`h-full${overlayInner}`}>
         {mounted ? children : null}
       </div>
     </div>