Add resizable sidebar panel with drag handle

client/src/components/Sidebar.tsx

@@ -19,6 +19,7 @@ import {
 } from "lucide-react";
 import { useStore, AgentStatus } from "../stores/useStore";
 import { Terminal } from "./Terminal";
+import { useResizable } from "../hooks/useResizable";
 
 const statusConfig: Record<AgentStatus, { label: string; color: string }> = {
   running: { label: "Running", color: "#22C55E" },
@@ -56,8 +57,16 @@ export function Sidebar() {
     nodes,
     setNewSessionModalOpen,
     setNewSessionForNodeId,
+    sidebarWidthPercent,
+    setSidebarWidthPercent,
   } = useStore();
 
+  const { isDragging, handleMouseDown } = useResizable({
+    minPercent: 20,
+    maxPercent: 60,
+    onResize: setSidebarWidthPercent,
+  });
+
   const session = selectedNodeId ? sessions.get(selectedNodeId) : null;
   const node = selectedNodeId ? nodes.find(n => n.id === selectedNodeId) : null;
 
@@ -108,8 +117,16 @@ export function Sidebar() {
           animate={{ x: 0, opacity: 1 }}
           exit={{ x: "100%", opacity: 0 }}
           transition={{ type: "spring", stiffness: 400, damping: 40 }}
-          className="fixed right-0 top-14 bottom-0 w-full max-w-lg z-50 flex flex-col bg-canvas-dark border-l border-border"
+          className="fixed right-0 top-14 bottom-0 z-50 flex flex-col bg-canvas-dark border-l border-border"
+          style={{ width: `${sidebarWidthPercent}vw` }}
         >
+          {/* Drag handle */}
+          <div
+            onMouseDown={handleMouseDown}
+            className={`absolute left-0 top-0 bottom-0 w-1.5 cursor-col-resize transition-colors z-10 ${
+              isDragging ? "bg-violet-500" : "hover:bg-violet-500/40"
+            }`}
+          />
           {/* Header */}
           <div className="flex-shrink-0 px-4 py-3 border-b border-border">
             <div className="flex items-center gap-3">

client/src/hooks/useResizable.ts

@@ -0,0 +1,66 @@
+import { useState, useCallback, useEffect } from "react";
+
+interface UseResizableOptions {
+  minPercent?: number;
+  maxPercent?: number;
+  onResize?: (percent: number) => void;
+}
+
+interface UseResizableReturn {
+  isDragging: boolean;
+  handleMouseDown: (e: React.MouseEvent) => void;
+}
+
+export function useResizable({
+  minPercent = 20,
+  maxPercent = 60,
+  onResize,
+}: UseResizableOptions = {}): UseResizableReturn {
+  const [isDragging, setIsDragging] = useState(false);
+
+  const handleMouseDown = useCallback((e: React.MouseEvent) => {
+    e.preventDefault();
+    setIsDragging(true);
+  }, []);
+
+  useEffect(() => {
+    if (!isDragging) return;
+
+    const handleMouseMove = (e: MouseEvent) => {
+      // Calculate percentage: sidebar is on the right, so width = distance from mouse to right edge
+      const percent = ((window.innerWidth - e.clientX) / window.innerWidth) * 100;
+      const clampedPercent = Math.min(maxPercent, Math.max(minPercent, percent));
+      onResize?.(clampedPercent);
+    };
+
+    const handleMouseUp = () => {
+      setIsDragging(false);
+    };
+
+    document.addEventListener("mousemove", handleMouseMove);
+    document.addEventListener("mouseup", handleMouseUp);
+
+    return () => {
+      document.removeEventListener("mousemove", handleMouseMove);
+      document.removeEventListener("mouseup", handleMouseUp);
+    };
+  }, [isDragging, minPercent, maxPercent, onResize]);
+
+  // Prevent text selection and set cursor globally during drag
+  useEffect(() => {
+    if (isDragging) {
+      document.body.style.cursor = "col-resize";
+      document.body.style.userSelect = "none";
+    } else {
+      document.body.style.cursor = "";
+      document.body.style.userSelect = "";
+    }
+
+    return () => {
+      document.body.style.cursor = "";
+      document.body.style.userSelect = "";
+    };
+  }, [isDragging]);
+
+  return { isDragging, handleMouseDown };
+}

client/src/stores/useStore.ts

@@ -35,6 +35,16 @@ export interface AgentSession {
   currentTool?: string;
 }
 
+const getInitialSidebarWidth = (): number => {
+  if (typeof window === 'undefined') return 35;
+  const stored = localStorage.getItem('openui:sidebarWidthPercent');
+  if (stored) {
+    const parsed = parseFloat(stored);
+    if (!isNaN(parsed) && parsed >= 20 && parsed <= 60) return parsed;
+  }
+  return 35; // default ~512px equivalent on 1440px screens
+};
+
 interface AppState {
   // Config
   launchCwd: string;
@@ -62,6 +72,8 @@ interface AppState {
   setSelectedNodeId: (id: string | null) => void;
   sidebarOpen: boolean;
   setSidebarOpen: (open: boolean) => void;
+  sidebarWidthPercent: number;
+  setSidebarWidthPercent: (percent: number) => void;
   addAgentModalOpen: boolean;
   setAddAgentModalOpen: (open: boolean) => void;
   newSessionModalOpen: boolean;
@@ -123,6 +135,11 @@ export const useStore = create<AppState>((set) => ({
   setSelectedNodeId: (id) => set({ selectedNodeId: id }),
   sidebarOpen: false,
   setSidebarOpen: (open) => set({ sidebarOpen: open }),
+  sidebarWidthPercent: getInitialSidebarWidth(),
+  setSidebarWidthPercent: (percent) => {
+    localStorage.setItem('openui:sidebarWidthPercent', String(percent));
+    set({ sidebarWidthPercent: percent });
+  },
   addAgentModalOpen: false,
   setAddAgentModalOpen: (open) => set({ addAgentModalOpen: open }),
   newSessionModalOpen: false,