feat: add drag-to-resize sidebar and right panel, improve UI spacing

- Add dynamic width state management for sidebar (200-400px) and right panel (240-480px)
- Implement drag-to-resize functionality with useResize hook and visual feedback
- Persist panel widths to localStorage for consistent UX across sessions
- Increase sidebar toggle padding from pl-20 to pl-24 to avoid macOS traffic lights
- Match "Select a folder to start..." font size to textarea (text-sm)
- Remove redundant close button from RightPanelHeader
- Disable CSS transitions during resize for smoother dragging experience

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

src/renderer/src/components/MessageInput.tsx

@@ -76,7 +76,7 @@ export function MessageInput({
             {/* Folder selection prompt */}
             <div className="flex items-center gap-3">
               <Folder className="h-5 w-5 text-muted-foreground flex-shrink-0" />
-              <span className="text-muted-foreground flex-1">Select a folder to start...</span>
+              <span className="text-sm text-muted-foreground flex-1">Select a folder to start...</span>
               <Button
                 variant="outline"
                 size="sm"

src/renderer/src/components/StatusBar.tsx

@@ -25,7 +25,7 @@ export function StatusBar({
   return (
     <div className={cn(
       "titlebar-drag-region flex h-11 items-center justify-between px-4",
-      needsTrafficLightPadding && "pl-20"
+      needsTrafficLightPadding && "pl-24"
     )}>
       {/* Left: Sidebar trigger + Session info */}
       <div className="titlebar-no-drag flex items-center gap-3">

src/renderer/src/components/layout/RightPanel.tsx

@@ -6,10 +6,13 @@ import * as React from 'react'
 import { PanelLeftIcon, PanelRightIcon } from 'lucide-react'
 import { cn } from '@/lib/utils'
 import { Button } from '@/components/ui/button'
-import { useUIStore } from '@/stores/uiStore'
+import {
+  useUIStore,
+  RIGHT_PANEL_MIN_WIDTH,
+  RIGHT_PANEL_MAX_WIDTH,
+} from '@/stores/uiStore'
 import { useSidebar } from '@/components/ui/sidebar'
-
-const RIGHT_PANEL_WIDTH = '20rem' // 320px
+import { useResize } from '@/hooks/useResize'
 
 interface RightPanelProps {
   children: React.ReactNode
@@ -18,25 +21,47 @@ interface RightPanelProps {
 
 export function RightPanel({ children, className }: RightPanelProps) {
   const isOpen = useUIStore((s) => s.rightPanelOpen)
+  const rightPanelWidth = useUIStore((s) => s.rightPanelWidth)
+  const setRightPanelWidth = useUIStore((s) => s.setRightPanelWidth)
+
+  const { isResizing, handleProps } = useResize({
+    width: rightPanelWidth,
+    minWidth: RIGHT_PANEL_MIN_WIDTH,
+    maxWidth: RIGHT_PANEL_MAX_WIDTH,
+    onWidthChange: setRightPanelWidth,
+    direction: 'left',
+  })
 
   return (
     <div
       className={cn(
         'hidden lg:block',
-        'transition-[width] duration-200 ease-linear',
+        // Disable transition during resize for smoother dragging
+        !isResizing && 'transition-[width] duration-200 ease-linear',
         isOpen ? 'w-[var(--right-panel-width)]' : 'w-0'
       )}
-      style={{ '--right-panel-width': RIGHT_PANEL_WIDTH } as React.CSSProperties}
+      style={{ '--right-panel-width': `${rightPanelWidth}px` } as React.CSSProperties}
     >
       <div
         className={cn(
           'fixed inset-y-0 right-0 z-10 h-svh border-l bg-background',
-          'transition-[transform,opacity] duration-200 ease-linear',
+          // Disable transition during resize for smoother dragging
+          !isResizing && 'transition-[transform,opacity,width] duration-200 ease-linear',
           isOpen ? 'translate-x-0 opacity-100' : 'translate-x-full opacity-0',
           className
         )}
-        style={{ width: RIGHT_PANEL_WIDTH }}
+        style={{ width: `${rightPanelWidth}px` }}
       >
+        {/* Resize handle */}
+        {isOpen && (
+          <div
+            className={cn(
+              'absolute inset-y-0 left-0 w-1 hover:bg-primary/20 active:bg-primary/30',
+              isResizing && 'bg-primary/30'
+            )}
+            {...handleProps}
+          />
+        )}
         {children}
       </div>
     </div>
@@ -97,23 +122,12 @@ export function RightPanelHeader({
   children,
   ...props
 }: React.ComponentProps<'div'>) {
-  const toggle = useUIStore((s) => s.toggleRightPanel)
-
   return (
     <div
-      className={cn('group flex h-11 items-center border-b px-4', className)}
+      className={cn('flex h-11 items-center border-b px-4', className)}
       {...props}
     >
       {children}
-      <Button
-        variant="ghost"
-        size="icon"
-        className="ml-auto size-7 opacity-0 group-hover:opacity-100 transition-opacity"
-        onClick={toggle}
-      >
-        <PanelRightIcon className="h-4 w-4" />
-        <span className="sr-only">Close Right Panel</span>
-      </Button>
     </div>
   )
 }

src/renderer/src/components/ui/sidebar.tsx

@@ -6,8 +6,14 @@ import { cva, type VariantProps } from "class-variance-authority"
 import { PanelLeftIcon } from "lucide-react"
 
 import { useIsMobile } from "@/hooks/use-mobile"
+import { useResize } from "@/hooks/useResize"
 import { cn } from "@/lib/utils"
 import { Button } from "@/components/ui/button"
+import {
+  useUIStore,
+  SIDEBAR_MIN_WIDTH,
+  SIDEBAR_MAX_WIDTH,
+} from "@/stores/uiStore"
 import { Input } from "@/components/ui/input"
 import { Separator } from "@/components/ui/separator"
 import {
@@ -27,7 +33,6 @@ import {
 
 const SIDEBAR_COOKIE_NAME = "sidebar_state"
 const SIDEBAR_COOKIE_MAX_AGE = 60 * 60 * 24 * 7
-const SIDEBAR_WIDTH = "16rem"
 const SIDEBAR_WIDTH_MOBILE = "18rem"
 const SIDEBAR_WIDTH_ICON = "3rem"
 const SIDEBAR_KEYBOARD_SHORTCUT = "b"
@@ -126,6 +131,9 @@ function SidebarProvider({
     [state, open, setOpen, isMobile, openMobile, setOpenMobile, toggleSidebar]
   )
 
+  // Get sidebar width from store
+  const sidebarWidth = useUIStore((s) => s.sidebarWidth)
+
   return (
     <SidebarContext.Provider value={contextValue}>
       <TooltipProvider delayDuration={0}>
@@ -133,7 +141,7 @@ function SidebarProvider({
           data-slot="sidebar-wrapper"
           style={
             {
-              "--sidebar-width": SIDEBAR_WIDTH,
+              "--sidebar-width": `${sidebarWidth}px`,
               "--sidebar-width-icon": SIDEBAR_WIDTH_ICON,
               ...style,
             } as React.CSSProperties
@@ -165,6 +173,17 @@ function Sidebar({
 }) {
   const { isMobile, state, openMobile, setOpenMobile } = useSidebar()
 
+  // Resize functionality
+  const sidebarWidth = useUIStore((s) => s.sidebarWidth)
+  const setSidebarWidth = useUIStore((s) => s.setSidebarWidth)
+  const { isResizing, handleProps } = useResize({
+    width: sidebarWidth,
+    minWidth: SIDEBAR_MIN_WIDTH,
+    maxWidth: SIDEBAR_MAX_WIDTH,
+    onWidthChange: setSidebarWidth,
+    direction: side === "left" ? "right" : "left",
+  })
+
   if (collapsible === "none") {
     return (
       <div
@@ -218,7 +237,9 @@ function Sidebar({
       <div
         data-slot="sidebar-gap"
         className={cn(
-          "relative w-(--sidebar-width) bg-transparent transition-[width] duration-200 ease-linear",
+          "relative w-(--sidebar-width) bg-transparent",
+          // Disable transition during resize for smoother dragging
+          !isResizing && "transition-[width] duration-200 ease-linear",
           "group-data-[collapsible=offcanvas]:w-0",
           "group-data-[side=right]:rotate-180",
           variant === "floating" || variant === "inset"
@@ -229,7 +250,9 @@ function Sidebar({
       <div
         data-slot="sidebar-container"
         className={cn(
-          "fixed inset-y-0 z-10 hidden h-svh w-(--sidebar-width) transition-[left,right,width] duration-200 ease-linear md:flex",
+          "fixed inset-y-0 z-10 hidden h-svh w-(--sidebar-width) md:flex",
+          // Disable transition during resize for smoother dragging
+          !isResizing && "transition-[left,right,width] duration-200 ease-linear",
           side === "left"
             ? "left-0 group-data-[collapsible=offcanvas]:left-[calc(var(--sidebar-width)*-1)]"
             : "right-0 group-data-[collapsible=offcanvas]:right-[calc(var(--sidebar-width)*-1)]",
@@ -248,6 +271,18 @@ function Sidebar({
         >
           {children}
         </div>
+        {/* Resize handle - only show when expanded */}
+        {state === "expanded" && (
+          <div
+            data-slot="sidebar-resize-handle"
+            className={cn(
+              "absolute inset-y-0 w-1 hover:bg-primary/20 active:bg-primary/30",
+              side === "left" ? "right-0" : "left-0",
+              isResizing && "bg-primary/30"
+            )}
+            {...handleProps}
+          />
+        )}
       </div>
     </div>
   )

src/renderer/src/hooks/useResize.ts

@@ -0,0 +1,91 @@
+/**
+ * Hook for drag-to-resize functionality
+ */
+import { useCallback, useEffect, useRef, useState } from 'react'
+
+interface UseResizeOptions {
+  /** Current width */
+  width: number
+  /** Minimum width */
+  minWidth: number
+  /** Maximum width */
+  maxWidth: number
+  /** Callback when width changes */
+  onWidthChange: (width: number) => void
+  /** Direction of resize: 'left' means drag from left edge, 'right' means drag from right edge */
+  direction: 'left' | 'right'
+}
+
+interface UseResizeReturn {
+  /** Whether currently resizing */
+  isResizing: boolean
+  /** Props to spread on the resize handle element */
+  handleProps: {
+    onMouseDown: (e: React.MouseEvent) => void
+    style: React.CSSProperties
+  }
+}
+
+export function useResize({
+  width,
+  minWidth,
+  maxWidth,
+  onWidthChange,
+  direction,
+}: UseResizeOptions): UseResizeReturn {
+  const [isResizing, setIsResizing] = useState(false)
+  const startXRef = useRef(0)
+  const startWidthRef = useRef(0)
+
+  const handleMouseDown = useCallback(
+    (e: React.MouseEvent) => {
+      e.preventDefault()
+      setIsResizing(true)
+      startXRef.current = e.clientX
+      startWidthRef.current = width
+    },
+    [width]
+  )
+
+  useEffect(() => {
+    if (!isResizing) return
+
+    const handleMouseMove = (e: MouseEvent) => {
+      const delta = e.clientX - startXRef.current
+      // For left sidebar, dragging right increases width
+      // For right panel, dragging left increases width
+      const newWidth =
+        direction === 'right'
+          ? startWidthRef.current + delta
+          : startWidthRef.current - delta
+      const clampedWidth = Math.max(minWidth, Math.min(maxWidth, newWidth))
+      onWidthChange(clampedWidth)
+    }
+
+    const handleMouseUp = () => {
+      setIsResizing(false)
+    }
+
+    document.addEventListener('mousemove', handleMouseMove)
+    document.addEventListener('mouseup', handleMouseUp)
+
+    // Add cursor style to body during resize
+    document.body.style.cursor = 'col-resize'
+    document.body.style.userSelect = 'none'
+
+    return () => {
+      document.removeEventListener('mousemove', handleMouseMove)
+      document.removeEventListener('mouseup', handleMouseUp)
+      document.body.style.cursor = ''
+      document.body.style.userSelect = ''
+    }
+  }, [isResizing, minWidth, maxWidth, onWidthChange, direction])
+
+  return {
+    isResizing,
+    handleProps: {
+      onMouseDown: handleMouseDown,
+      style: { cursor: 'col-resize' },
+    },
+  }
+}

src/renderer/src/stores/uiStore.ts

@@ -5,16 +5,29 @@
 import { create } from 'zustand'
 import { persist } from 'zustand/middleware'
 
+// Width constraints
+export const SIDEBAR_MIN_WIDTH = 200
+export const SIDEBAR_MAX_WIDTH = 400
+export const SIDEBAR_DEFAULT_WIDTH = 256
+
+export const RIGHT_PANEL_MIN_WIDTH = 240
+export const RIGHT_PANEL_MAX_WIDTH = 480
+export const RIGHT_PANEL_DEFAULT_WIDTH = 320
+
 interface UIStore {
   // Sidebar state
   sidebarOpen: boolean
+  sidebarWidth: number
   toggleSidebar: () => void
   setSidebarOpen: (open: boolean) => void
+  setSidebarWidth: (width: number) => void
 
   // Right panel state
   rightPanelOpen: boolean
+  rightPanelWidth: number
   toggleRightPanel: () => void
   setRightPanelOpen: (open: boolean) => void
+  setRightPanelWidth: (width: number) => void
 }
 
 export const useUIStore = create<UIStore>()(
@@ -22,13 +35,19 @@ export const useUIStore = create<UIStore>()(
     (set) => ({
       // Sidebar - default open
       sidebarOpen: true,
+      sidebarWidth: SIDEBAR_DEFAULT_WIDTH,
       toggleSidebar: () => set((state) => ({ sidebarOpen: !state.sidebarOpen })),
       setSidebarOpen: (open) => set({ sidebarOpen: open }),
+      setSidebarWidth: (width) =>
+        set({ sidebarWidth: Math.max(SIDEBAR_MIN_WIDTH, Math.min(SIDEBAR_MAX_WIDTH, width)) }),
 
       // Right panel - default open
       rightPanelOpen: true,
+      rightPanelWidth: RIGHT_PANEL_DEFAULT_WIDTH,
       toggleRightPanel: () => set((state) => ({ rightPanelOpen: !state.rightPanelOpen })),
       setRightPanelOpen: (open) => set({ rightPanelOpen: open }),
+      setRightPanelWidth: (width) =>
+        set({ rightPanelWidth: Math.max(RIGHT_PANEL_MIN_WIDTH, Math.min(RIGHT_PANEL_MAX_WIDTH, width)) }),
     }),
     {
       name: 'ui-state', // localStorage key