feat(ui): bring back make sidebar resizable with drag handle and persisted width

ui/desktop/src/components/Layout/AppLayout.tsx

@@ -1,4 +1,4 @@
-import React, { useEffect, useState } from 'react';
+import React, { useCallback, useEffect, useRef, useState } from 'react';
 import { IpcRendererEvent } from 'electron';
 import { Outlet, useLocation } from 'react-router-dom';
 import { motion } from 'framer-motion';
@@ -9,7 +9,7 @@ import ChatSessionsContainer from '../ChatSessionsContainer';
 import { useChatContext } from '../../contexts/ChatContext';
 import { NavigationProvider, useNavigationContext } from './NavigationContext';
 import { Navigation } from './NavigationPanel';
-import { NAV_DIMENSIONS, Z_INDEX } from './constants';
+import { Z_INDEX } from './constants';
 import { cn } from '../../utils';
 import { UserInput } from '../../types/message';
 
@@ -54,7 +54,41 @@ const AppLayoutContent: React.FC<AppLayoutContentProps> = ({ activeSessions }) =
     return () => window.electron.off('fullscreen-change', handler);
   }, [safeIsMacOS]);
 
-  const { isNavExpanded, setIsNavExpanded } = useNavigationContext();
+  const { isNavExpanded, setIsNavExpanded, navWidth, setNavWidth } = useNavigationContext();
+  const [isDragging, setIsDragging] = useState(false);
+  const isResizing = useRef(false);
+  const startX = useRef(0);
+  const startWidth = useRef(0);
+
+  const handleResizeMouseDown = useCallback(
+    (e: React.MouseEvent) => {
+      isResizing.current = true;
+      startX.current = e.clientX;
+      startWidth.current = navWidth;
+      setIsDragging(true);
+      e.preventDefault();
+    },
+    [navWidth]
+  );
+
+  useEffect(() => {
+    const handleMouseMove = (e: MouseEvent) => {
+      if (!isResizing.current) return;
+      setNavWidth(startWidth.current + (e.clientX - startX.current));
+    };
+    const handleMouseUp = () => {
+      if (isResizing.current) {
+        isResizing.current = false;
+        setIsDragging(false);
+      }
+    };
+    window.addEventListener('mousemove', handleMouseMove);
+    window.addEventListener('mouseup', handleMouseUp);
+    return () => {
+      window.removeEventListener('mousemove', handleMouseMove);
+      window.removeEventListener('mouseup', handleMouseUp);
+    };
+  }, [setNavWidth]);
 
   if (!chatContext) {
     throw new Error('AppLayoutContent must be used within ChatProvider');
@@ -93,14 +127,22 @@ const AppLayoutContent: React.FC<AppLayoutContentProps> = ({ activeSessions }) =
         <motion.div
           key="nav"
           initial={false}
-          animate={{ width: isNavExpanded ? NAV_DIMENSIONS.NAV_WIDTH : 0 }}
-          transition={{ type: 'spring', stiffness: 400, damping: 40 }}
+          animate={{ width: isNavExpanded ? navWidth : 0 }}
+          transition={
+            isDragging ? { duration: 0 } : { type: 'spring', stiffness: 400, damping: 40 }
+          }
           style={{ height: '100%' }}
           className="relative flex-shrink-0 overflow-hidden h-full p-2"
         >
           <div className="w-full h-full overflow-hidden rounded-xl border border-border-primary">
             <Navigation />
           </div>
+          {isNavExpanded && (
+            <div
+              className="absolute right-0 top-0 h-full w-2 cursor-col-resize hover:bg-border-primary/30 transition-colors"
+              onMouseDown={handleResizeMouseDown}
+            />
+          )}
         </motion.div>
 
         {/* Main content — no border / no card; just flows on the canvas. */}

ui/desktop/src/components/Layout/NavigationContext.tsx

@@ -7,6 +7,7 @@ import React, {
   useRef,
   useState,
 } from 'react';
+import { NAV_DIMENSIONS } from './constants';
 
 /**
  * When the window is narrower than this many CSS pixels, we auto-collapse
@@ -15,9 +16,14 @@ import React, {
  */
 const NARROW_WINDOW_THRESHOLD = 700;
 
+export const MIN_NAV_WIDTH = 160;
+export const MAX_NAV_WIDTH = 400;
+
 interface NavigationContextValue {
   isNavExpanded: boolean;
   setIsNavExpanded: (expanded: boolean) => void;
+  navWidth: number;
+  setNavWidth: (width: number) => void;
 }
 
 const NavigationContext = createContext<NavigationContextValue | null>(null);
@@ -49,6 +55,23 @@ export const NavigationProvider: React.FC<NavigationProviderProps> = ({ children
     localStorage.setItem('navigation_expanded', String(expanded));
   }, []);
 
+  const [navWidth, setNavWidthState] = useState<number>(() => {
+    const stored = localStorage.getItem('navigation_width');
+    if (stored) {
+      const parsed = parseInt(stored, 10);
+      if (!isNaN(parsed) && parsed >= MIN_NAV_WIDTH && parsed <= MAX_NAV_WIDTH) {
+        return parsed;
+      }
+    }
+    return NAV_DIMENSIONS.NAV_WIDTH;
+  });
+
+  const setNavWidth = useCallback((width: number) => {
+    const clamped = Math.min(MAX_NAV_WIDTH, Math.max(MIN_NAV_WIDTH, width));
+    setNavWidthState(clamped);
+    localStorage.setItem('navigation_width', String(clamped));
+  }, []);
+
   const isNavExpandedRef = useRef(isNavExpanded);
   useEffect(() => {
     isNavExpandedRef.current = isNavExpanded;
@@ -90,6 +113,8 @@ export const NavigationProvider: React.FC<NavigationProviderProps> = ({ children
   const value: NavigationContextValue = {
     isNavExpanded,
     setIsNavExpanded,
+    navWidth,
+    setNavWidth,
   };
 
   return <NavigationContext.Provider value={value}>{children}</NavigationContext.Provider>;