feat(mobile): single-pane stack + long-press tab menu + swipe-to-close

- Workspace: on mobile renders only panes[activePaneIdx] (rest skipped).
  When panes.length > 1, adds a horizontal pane-navigator strip built
  from SwipeablePaneTab above the active pane. URL state ?pane=<paneId>
  written by switchActivePane (user-initiated only) and read on URL
  change (back-button + deep-link). Bare URL resets activePaneIdx to 0.
- useLongPress: 500ms touchstart timer; on fire, dispatches a synthetic
  contextmenu event on target.closest('[data-tab-id]') so the existing
  Radix ContextMenuTrigger opens at the touch coordinates. Suppresses
  the synthetic click that follows touchend. Cancels on touchmove /
  touchend / touchcancel.
- ChatTabBar: each tab gets data-tab-id, touch handlers wired to
  useLongPress, and WebkitTouchCallout: 'none' to disable iOS Safari's
  text-selection callout.
- SwipeablePaneTab: tracks horizontal drag; bails if vertical delta
  exceeds 30px (so vertical scroll still works); past 60px on release
  fires onClose (removePane), else snaps back. Opacity fades 1->0.4
  approaching the threshold. Hand-rolled per spec.
- Pane drag-and-drop disabled on mobile (HTML5 drag is broken on touch
  anyway; mobile uses the navigator + swipe-to-close instead).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/web/src/components/ChatTabBar.tsx

@@ -8,6 +8,7 @@ import {
   ContextMenuSeparator,
   ContextMenuTrigger,
 } from '@/components/ui/context-menu';
+import { useLongPress } from '@/hooks/useLongPress';
 import { cn } from '@/lib/utils';
 
 interface Props {
@@ -40,6 +41,18 @@ export function ChatTabBar({
   const [renamingId, setRenamingId] = useState<string | null>(null);
   const [renameValue, setRenameValue] = useState('');
 
+  // Long-press: dispatch a synthetic contextmenu event on the tab so the
+  // existing Radix ContextMenuTrigger opens at the touch coordinates. Works
+  // because asChild composition makes the tab div the trigger element.
+  const longPress = useLongPress(({ clientX, clientY, target }) => {
+    if (!target || !(target instanceof Element)) return;
+    const tab = target.closest('[data-tab-id]') as HTMLElement | null;
+    if (!tab) return;
+    tab.dispatchEvent(
+      new MouseEvent('contextmenu', { bubbles: true, cancelable: true, clientX, clientY }),
+    );
+  });
+
   function startRename(chatId: string, currentName: string | null) {
     setRenamingId(chatId);
     setRenameValue(currentName ?? '');
@@ -63,7 +76,13 @@ export function ChatTabBar({
           <ContextMenu key={chat.id}>
             <ContextMenuTrigger asChild>
               <div
+                data-tab-id={chat.id}
                 onClick={() => onSwitchTab(tabIdx)}
+                onTouchStart={longPress.onTouchStart}
+                onTouchMove={longPress.onTouchMove}
+                onTouchEnd={longPress.onTouchEnd}
+                onTouchCancel={longPress.onTouchCancel}
+                style={{ WebkitTouchCallout: 'none' }}
                 className={cn(
                   'group flex items-center gap-1.5 px-3 py-1.5 text-xs border-r border-border cursor-default select-none shrink-0',
                   isActive

apps/web/src/components/SwipeablePaneTab.tsx

@@ -0,0 +1,103 @@
+import { useRef, useState } from 'react';
+import type { TouchEvent } from 'react';
+import { cn } from '@/lib/utils';
+
+interface Props {
+  label: string;
+  isActive: boolean;
+  onTap: () => void;
+  onClose: () => void;
+  canClose: boolean;
+}
+
+const CLOSE_THRESHOLD = 60;
+const MAX_TRAVEL = 120;
+const VERTICAL_BAIL = 30;
+
+// Pane tab with horizontal swipe-to-close (mobile only). Tracks horizontal
+// finger movement; if vertical exceeds VERTICAL_BAIL the gesture is cancelled
+// (so vertical scroll still works). On release past CLOSE_THRESHOLD, the
+// onClose callback fires. Otherwise the tab snaps back. Hand-rolled per spec.
+export function SwipeablePaneTab({ label, isActive, onTap, onClose, canClose }: Props) {
+  const [translateX, setTranslateX] = useState(0);
+  const [dragging, setDragging] = useState(false);
+  const startRef = useRef<{ x: number; y: number; bailed: boolean } | null>(null);
+
+  const onTouchStart = (e: TouchEvent) => {
+    if (!canClose) return;
+    const t = e.touches[0];
+    if (!t) return;
+    startRef.current = { x: t.clientX, y: t.clientY, bailed: false };
+    setDragging(true);
+  };
+
+  const onTouchMove = (e: TouchEvent) => {
+    const start = startRef.current;
+    if (!start || start.bailed) return;
+    const t = e.touches[0];
+    if (!t) return;
+    const dx = t.clientX - start.x;
+    const dy = t.clientY - start.y;
+    if (Math.abs(dy) > VERTICAL_BAIL) {
+      start.bailed = true;
+      setTranslateX(0);
+      setDragging(false);
+      return;
+    }
+    if (dx < 0) {
+      setTranslateX(Math.max(dx, -MAX_TRAVEL));
+    } else {
+      setTranslateX(0);
+    }
+  };
+
+  const onTouchEnd = () => {
+    const start = startRef.current;
+    startRef.current = null;
+    setDragging(false);
+    if (!start || start.bailed) {
+      setTranslateX(0);
+      return;
+    }
+    const tx = translateX;
+    if (tx <= -CLOSE_THRESHOLD) {
+      onClose();
+      // Don't reset translateX; the parent will unmount this tab.
+    } else {
+      setTranslateX(0);
+    }
+  };
+
+  // Opacity fades from 1 -> 0.4 as the tab approaches the close threshold.
+  const opacity =
+    translateX < 0
+      ? Math.max(0.4, 1 - (Math.abs(translateX) / CLOSE_THRESHOLD) * 0.6)
+      : 1;
+
+  return (
+    <button
+      type="button"
+      onClick={onTap}
+      onTouchStart={onTouchStart}
+      onTouchMove={onTouchMove}
+      onTouchEnd={onTouchEnd}
+      onTouchCancel={onTouchEnd}
+      style={{
+        transform: `translateX(${translateX}px)`,
+        opacity,
+        // Only animate when releasing (snap-back); during drag the transform
+        // tracks the finger 1:1 for a tight feel.
+        transition: dragging ? undefined : 'transform 0.15s ease, opacity 0.15s ease',
+      }}
+      className={cn(
+        'shrink-0 px-3 py-2 text-xs rounded min-h-[44px] min-w-[44px]',
+        isActive
+          ? 'bg-background text-foreground border'
+          : 'text-muted-foreground hover:bg-muted/40',
+      )}
+      aria-current={isActive ? 'true' : undefined}
+    >
+      <span className="truncate max-w-[140px] inline-block">{label}</span>
+    </button>
+  );
+}

apps/web/src/components/Workspace.tsx

@@ -1,11 +1,14 @@
-import { useCallback } from 'react';
+import { useCallback, useEffect } from 'react';
+import { useLocation, useNavigate, useSearchParams } from 'react-router-dom';
 import { PanelRight, MessageSquare, Terminal, Bot } from 'lucide-react';
 import type { Chat, WorkspacePane } from '@/api/types';
 import { useWorkspacePanes, MAX_PANES } from '@/hooks/useWorkspacePanes';
 import { useSessionChats } from '@/hooks/useSessionChats';
+import { useViewport } from '@/hooks/useViewport';
 import { ChatPane } from '@/components/panes/ChatPane';
 import { ChatTabBar } from '@/components/ChatTabBar';
 import { SessionLandingPage } from '@/components/SessionLandingPage';
+import { SwipeablePaneTab } from '@/components/SwipeablePaneTab';
 import {
   DropdownMenu,
   DropdownMenuContent,
@@ -67,12 +70,59 @@ export function Workspace({ sessionId, projectId }: Props) {
     initializeFirstChatIfEmpty,
   });
 
+  const { isMobile } = useViewport();
+  const [searchParams] = useSearchParams();
+  const navigate = useNavigate();
+  const location = useLocation();
+
+  // URL -> state (mobile only). Handles deep-link arrival and Back button
+  // history pops. On a bare URL (no ?pane), reset to first pane so Back
+  // from a ?pane URL returns the user to a sensible default.
+  useEffect(() => {
+    if (!isMobile || panes.length === 0) return;
+    const paneId = searchParams.get('pane');
+    if (!paneId) {
+      if (activePaneIdx !== 0) setActivePaneIdx(0);
+      return;
+    }
+    const idx = panes.findIndex((p) => p.id === paneId);
+    if (idx >= 0 && idx !== activePaneIdx) setActivePaneIdx(idx);
+  }, [isMobile, searchParams, panes, activePaneIdx, setActivePaneIdx]);
+
+  // Switch active pane and push URL (mobile only). User-initiated only;
+  // never called from URL-sync effect.
+  const switchActivePane = useCallback(
+    (idx: number) => {
+      setActivePaneIdx(idx);
+      if (isMobile) {
+        const pane = panes[idx];
+        if (!pane) return;
+        const params = new URLSearchParams(location.search);
+        params.set('pane', pane.id);
+        navigate(`${location.pathname}?${params.toString()}`);
+      }
+    },
+    [setActivePaneIdx, isMobile, panes, navigate, location.pathname, location.search],
+  );
+
   function chatsForPane(pane: WorkspacePane): Chat[] {
     return pane.chatIds
       .map((id) => chats.find((c) => c.id === id))
       .filter((c): c is Chat => c !== undefined);
   }
 
+  function paneLabel(pane: WorkspacePane): string {
+    const activeChatId = pane.chatId;
+    if (activeChatId) {
+      const chat = chats.find((c) => c.id === activeChatId);
+      if (chat) return chat.name ?? 'New chat';
+    }
+    if (pane.kind === 'chat') return 'Chat';
+    if (pane.kind === 'terminal') return 'Terminal';
+    if (pane.kind === 'agent') return 'Agent';
+    return 'Empty';
+  }
+
   return (
     <div className="flex flex-col h-full min-h-0">
       <div className="flex items-center gap-2 border-b border-border bg-muted/20 px-3 py-1.5 shrink-0">
@@ -82,7 +132,7 @@ export function Workspace({ sessionId, projectId }: Props) {
               type="button"
               disabled={panes.length >= MAX_PANES}
               className={cn(
-                'flex items-center gap-1 text-xs px-2 py-1 rounded hover:bg-muted',
+                'flex items-center gap-1 text-xs px-2 py-1 rounded hover:bg-muted max-md:min-h-[44px] max-md:px-3',
                 panes.length >= MAX_PANES && 'opacity-40 cursor-not-allowed hover:bg-transparent'
               )}
             >
@@ -104,30 +154,51 @@ export function Workspace({ sessionId, projectId }: Props) {
         </DropdownMenu>
       </div>
 
+      {isMobile && panes.length > 1 && (
+        <div className="flex items-center gap-1 overflow-x-auto border-b border-border bg-muted/10 px-2 py-1 shrink-0">
+          {panes.map((pane, idx) => (
+            <SwipeablePaneTab
+              key={pane.id}
+              label={paneLabel(pane)}
+              isActive={idx === activePaneIdx}
+              onTap={() => switchActivePane(idx)}
+              onClose={() => removePane(idx)}
+              canClose={panes.length > 1}
+            />
+          ))}
+        </div>
+      )}
+
       <div
-        className="flex-1 grid min-h-0"
-        style={{
-          gridTemplateColumns: `repeat(${panes.length}, minmax(0, 1fr))`,
-        }}
+        className={cn('flex-1 min-h-0', isMobile ? 'flex' : 'grid')}
+        style={
+          isMobile
+            ? undefined
+            : { gridTemplateColumns: `repeat(${panes.length}, minmax(0, 1fr))` }
+        }
       >
-        {panes.map((pane, idx) => (
+        {panes.map((pane, idx) => {
+          const visible = !isMobile || idx === activePaneIdx;
+          if (!visible) return null;
+          return (
           <div
             key={pane.id}
             className={cn(
               'flex flex-col h-full min-h-0 border-r border-border last:border-r-0 relative',
-              idx === activePaneIdx && 'ring-1 ring-inset ring-ring/20',
-              dragOverIdx === idx && draggingIdxRef.current !== idx &&
+              isMobile ? 'flex-1 w-full' : undefined,
+              !isMobile && idx === activePaneIdx && 'ring-1 ring-inset ring-ring/20',
+              !isMobile && dragOverIdx === idx && draggingIdxRef.current !== idx &&
                 'before:absolute before:inset-y-0 before:left-0 before:w-0.5 before:bg-primary before:z-10'
             )}
             onClick={() => setActivePaneIdx(idx)}
-            onDragOver={panes.length > 1 ? handlePaneDragOver(idx) : undefined}
-            onDragLeave={panes.length > 1 ? handlePaneDragLeave : undefined}
-            onDrop={panes.length > 1 ? handlePaneDrop(idx) : undefined}
+            onDragOver={!isMobile && panes.length > 1 ? handlePaneDragOver(idx) : undefined}
+            onDragLeave={!isMobile && panes.length > 1 ? handlePaneDragLeave : undefined}
+            onDrop={!isMobile && panes.length > 1 ? handlePaneDrop(idx) : undefined}
           >
             <div
-              draggable={panes.length > 1}
-              onDragStart={panes.length > 1 ? handlePaneDragStart(idx) : undefined}
-              onDragEnd={panes.length > 1 ? handlePaneDragEnd : undefined}
+              draggable={!isMobile && panes.length > 1}
+              onDragStart={!isMobile && panes.length > 1 ? handlePaneDragStart(idx) : undefined}
+              onDragEnd={!isMobile && panes.length > 1 ? handlePaneDragEnd : undefined}
             >
               <ChatTabBar
                 pane={pane}
@@ -165,7 +236,8 @@ export function Workspace({ sessionId, projectId }: Props) {
               )}
             </div>
           </div>
-        ))}
+          );
+        })}
       </div>
     </div>
   );

apps/web/src/hooks/useLongPress.ts

@@ -0,0 +1,75 @@
+import { useCallback, useRef } from 'react';
+import type { TouchEvent } from 'react';
+
+interface LongPressHandlers {
+  onTouchStart: (e: TouchEvent) => void;
+  onTouchMove: (e: TouchEvent) => void;
+  onTouchEnd: (e: TouchEvent) => void;
+  onTouchCancel: (e: TouchEvent) => void;
+}
+
+interface Options {
+  ms?: number;
+  // Suppress the synthetic click that follows touchend when long-press fired.
+  suppressClickOnFire?: boolean;
+}
+
+// Hand-rolled long-press detector. Starts a timer on touchstart; cancels on
+// touchmove or early touchend; fires the callback on timer expiry. Caller is
+// expected to suppress text-selection callout via CSS (-webkit-touch-callout).
+export function useLongPress(
+  callback: (touch: { clientX: number; clientY: number; target: EventTarget | null }) => void,
+  { ms = 500, suppressClickOnFire = true }: Options = {},
+): LongPressHandlers {
+  const timerRef = useRef<number | null>(null);
+  const firedRef = useRef(false);
+
+  const clear = useCallback(() => {
+    if (timerRef.current !== null) {
+      window.clearTimeout(timerRef.current);
+      timerRef.current = null;
+    }
+  }, []);
+
+  const onTouchStart = useCallback(
+    (e: TouchEvent) => {
+      firedRef.current = false;
+      const touch = e.touches[0];
+      if (!touch) return;
+      const x = touch.clientX;
+      const y = touch.clientY;
+      const target = e.target;
+      clear();
+      timerRef.current = window.setTimeout(() => {
+        firedRef.current = true;
+        callback({ clientX: x, clientY: y, target });
+      }, ms);
+    },
+    [callback, ms, clear],
+  );
+
+  const onTouchMove = useCallback(() => {
+    clear();
+  }, [clear]);
+
+  const onTouchEnd = useCallback(
+    (e: TouchEvent) => {
+      clear();
+      if (firedRef.current && suppressClickOnFire) {
+        // Block the synthetic click that follows touchend; the long-press
+        // already handled the gesture.
+        e.preventDefault();
+      }
+    },
+    [clear, suppressClickOnFire],
+  );
+
+  const onTouchCancel = useCallback(
+    (_e: TouchEvent) => {
+      clear();
+    },
+    [clear],
+  );
+
+  return { onTouchStart, onTouchMove, onTouchEnd, onTouchCancel };
+}