feat: add sidebar collapse, category/tag filtering, and workspace CRUD (Phase D)

- Sidebar collapse/expand toggle with icon-only rail mode (persisted)
- Sidebar category/tag clicks navigate to /trees with URL params
- TreeLibraryPage syncs filters from URL search params bidirectionally
- Workspace create modal with icon picker and auto-slug generation
- TopBar logo adapts to collapsed sidebar state

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/components/layout/AppLayout.tsx

@@ -15,6 +15,7 @@ export function AppLayout() {
   const { user, logout } = useAuthStore()
   const { effectiveRole } = usePermissions()
   const fetchWorkspaces = useWorkspaceStore(s => s.fetchWorkspaces)
+  const sidebarCollapsed = useWorkspaceStore(s => s.sidebarCollapsed)
   const [mobileMenuOpen, setMobileMenuOpen] = useState(false)
 
   // Fetch workspaces on mount
@@ -65,7 +66,7 @@ export function AppLayout() {
   ]
 
   return (
-    <div className="app-shell">
+    <div className={cn('app-shell', sidebarCollapsed && 'app-shell--collapsed')}>
       {/* Top Bar - spans full width */}
       <TopBar />
 

frontend/src/components/layout/NavItem.tsx

@@ -8,9 +8,10 @@ interface NavItemProps {
   label: string
   badge?: number | 'dot'
   matchPaths?: string[]
+  collapsed?: boolean
 }
 
-export function NavItem({ href, icon: Icon, label, badge, matchPaths }: NavItemProps) {
+export function NavItem({ href, icon: Icon, label, badge, matchPaths, collapsed }: NavItemProps) {
   const location = useLocation()
   const isActive = matchPaths
     ? matchPaths.some(p => location.pathname.startsWith(p))
@@ -18,6 +19,31 @@ export function NavItem({ href, icon: Icon, label, badge, matchPaths }: NavItemP
       ? location.pathname === '/'
       : location.pathname.startsWith(href)
 
+  if (collapsed) {
+    return (
+      <Link
+        to={href}
+        className={cn(
+          'group relative flex items-center justify-center rounded-lg p-2 transition-all duration-120',
+          isActive
+            ? 'bg-[hsl(var(--sidebar-active))] text-foreground'
+            : 'text-muted-foreground hover:bg-[hsl(var(--sidebar-hover))] hover:text-foreground'
+        )}
+        title={label}
+      >
+        {isActive && (
+          <div className="absolute left-0 top-1/2 h-6 w-[3px] -translate-y-1/2 rounded-r-full bg-gradient-brand" />
+        )}
+        <Icon size={18} className={cn('shrink-0', isActive ? 'opacity-100' : 'opacity-70')} />
+        {badge !== undefined && badge !== 0 && badge !== 'dot' && (
+          <span className="absolute -right-0.5 -top-0.5 flex h-4 w-4 items-center justify-center rounded-full bg-primary text-[0.5rem] font-bold text-primary-foreground">
+            {badge}
+          </span>
+        )}
+      </Link>
+    )
+  }
+
   return (
     <Link
       to={href}

frontend/src/components/layout/Sidebar.tsx

@@ -1,5 +1,6 @@
 import { useEffect, useState } from 'react'
-import { LayoutGrid, Box, PenLine, Clock, FileText, Bookmark, Users, Settings } from 'lucide-react'
+import { useNavigate, useLocation } from 'react-router-dom'
+import { LayoutGrid, Box, PenLine, Clock, FileText, Bookmark, Users, Settings, PanelLeftClose, PanelLeftOpen } from 'lucide-react'
 import { useWorkspaceStore } from '@/store/workspaceStore'
 import { getWorkspaceLabels } from '@/constants/workspaceLabels'
 import { WorkspaceSwitcher } from '@/components/workspace/WorkspaceSwitcher'
@@ -18,6 +19,8 @@ interface CategoryItem {
 export function Sidebar() {
   const activeWorkspace = useWorkspaceStore(s => s.getActiveWorkspace())
   const activeWorkspaceId = useWorkspaceStore(s => s.activeWorkspaceId)
+  const sidebarCollapsed = useWorkspaceStore(s => s.sidebarCollapsed)
+  const toggleSidebar = useWorkspaceStore(s => s.toggleSidebar)
   const labels = getWorkspaceLabels(activeWorkspace?.slug)
 
   const [categories, setCategories] = useState<CategoryItem[]>([])
@@ -50,50 +53,110 @@ export function Sidebar() {
     fetchData()
   }, [activeWorkspaceId])
 
+  const navigate = useNavigate()
+  const location = useLocation()
+
+  // Sync active filters from URL when on /trees page
+  useEffect(() => {
+    if (location.pathname === '/trees') {
+      const params = new URLSearchParams(location.search)
+      setActiveCategoryId(params.get('category') || null)
+      const tagsParam = params.get('tags')
+      setActiveTags(tagsParam ? tagsParam.split(',') : [])
+    }
+  }, [location.pathname, location.search])
+
+  const handleCategorySelect = (id: string | null) => {
+    setActiveCategoryId(id)
+    const params = new URLSearchParams(location.search)
+    if (id) {
+      params.set('category', id)
+    } else {
+      params.delete('category')
+    }
+    navigate(`/trees?${params.toString()}`)
+  }
+
   const handleTagClick = (tag: string) => {
-    setActiveTags(prev =>
+    const next = activeTags.includes(tag)
-      prev.includes(tag) ? prev.filter(t => t !== tag) : [...prev, tag]
+      ? activeTags.filter(t => t !== tag)
-    )
+      : [...activeTags, tag]
+    setActiveTags(next)
+    const params = new URLSearchParams(location.search)
+    if (next.length > 0) {
+      params.set('tags', next.join(','))
+    } else {
+      params.delete('tags')
+    }
+    navigate(`/trees?${params.toString()}`)
   }
 
   return (
     <nav className="sidebar flex flex-col border-r border-border bg-[hsl(var(--sidebar-bg))]">
-      {/* Workspace Switcher */}
+      {sidebarCollapsed ? (
-      <WorkspaceSwitcher />
+        <>
+          {/* Collapsed: icon-only nav */}
+          <div className="px-2 py-3 space-y-1">
+            <NavItem href="/" icon={LayoutGrid} label="" collapsed />
+            <NavItem href="/trees" icon={Box} label="" matchPaths={['/trees', '/flows']} collapsed />
+            <NavItem href="/my-trees" icon={PenLine} label="" collapsed />
+            <NavItem href="/sessions" icon={Clock} label="" badge={activeSessionCount || undefined} collapsed />
+            <NavItem href="/shares" icon={FileText} label="" collapsed />
+            <NavItem href="/step-library" icon={Bookmark} label="" collapsed />
+          </div>
+        </>
+      ) : (
+        <>
+          {/* Workspace Switcher */}
+          <WorkspaceSwitcher />
 
-      <div className="border-b border-[hsl(var(--border-subtle))]" />
+          <div className="border-b border-[hsl(var(--border-subtle))]" />
 
-      {/* Primary Navigation */}
+          {/* Primary Navigation */}
-      <div className="px-3 py-2 space-y-0.5">
+          <div className="px-3 py-2 space-y-0.5">
-        <NavItem href="/" icon={LayoutGrid} label="Dashboard" />
+            <NavItem href="/" icon={LayoutGrid} label="Dashboard" />
-        <NavItem href="/trees" icon={Box} label={labels.allItems} matchPaths={['/trees', '/flows']} />
+            <NavItem href="/trees" icon={Box} label={labels.allItems} matchPaths={['/trees', '/flows']} />
-        <NavItem href="/my-trees" icon={PenLine} label={labels.editor} />
+            <NavItem href="/my-trees" icon={PenLine} label={labels.editor} />
-        <NavItem href="/sessions" icon={Clock} label="Sessions" badge={activeSessionCount || undefined} />
+            <NavItem href="/sessions" icon={Clock} label="Sessions" badge={activeSessionCount || undefined} />
-        <NavItem href="/shares" icon={FileText} label="Exports" />
+            <NavItem href="/shares" icon={FileText} label="Exports" />
-        <NavItem href="/step-library" icon={Bookmark} label="Step Library" badge="dot" />
+            <NavItem href="/step-library" icon={Bookmark} label="Step Library" badge="dot" />
-      </div>
+          </div>
 
-      <div className="border-b border-[hsl(var(--border-subtle))]" />
+          <div className="border-b border-[hsl(var(--border-subtle))]" />
 
-      {/* Categories */}
+          {/* Categories */}
-      <CategoryList
+          <CategoryList
-        categories={categories}
+            categories={categories}
-        activeId={activeCategoryId}
+            activeId={activeCategoryId}
-        onSelect={setActiveCategoryId}
+            onSelect={handleCategorySelect}
-      />
+          />
 
-      <div className="border-b border-[hsl(var(--border-subtle))]" />
+          <div className="border-b border-[hsl(var(--border-subtle))]" />
 
-      {/* Tags */}
+          {/* Tags */}
-      <TagCloud tags={tags} activeTags={activeTags} onTagClick={handleTagClick} />
+          <TagCloud tags={tags} activeTags={activeTags} onTagClick={handleTagClick} />
+        </>
+      )}
 
       {/* Spacer */}
       <div className="flex-1" />
 
       {/* Footer */}
       <div className="border-t border-[hsl(var(--border-subtle))] px-3 py-2 space-y-0.5">
-        <NavItem href="/account" icon={Users} label="Team" />
+        {!sidebarCollapsed && (
-        <NavItem href="/account" icon={Settings} label="Settings" />
+          <>
+            <NavItem href="/account" icon={Users} label="Team" />
+            <NavItem href="/account" icon={Settings} label="Settings" />
+          </>
+        )}
+        <button
+          onClick={toggleSidebar}
+          className="flex w-full items-center gap-3 rounded-lg px-3 py-2 text-[0.8125rem] font-medium text-muted-foreground hover:bg-[hsl(var(--sidebar-hover))] hover:text-foreground transition-colors"
+          title={sidebarCollapsed ? 'Expand sidebar' : 'Collapse sidebar'}
+        >
+          {sidebarCollapsed ? <PanelLeftOpen size={18} /> : <PanelLeftClose size={18} />}
+          {!sidebarCollapsed && <span>Collapse</span>}
+        </button>
       </div>
     </nav>
   )

frontend/src/components/layout/TopBar.tsx

@@ -14,6 +14,7 @@ export function TopBar() {
   const { user, logout } = useAuthStore()
   const { effectiveRole, isSuperAdmin } = usePermissions()
   const activeWorkspace = useWorkspaceStore(s => s.getActiveWorkspace())
+  const sidebarCollapsed = useWorkspaceStore(s => s.sidebarCollapsed)
   const labels = getWorkspaceLabels(activeWorkspace?.slug)
 
   const [userMenuOpen, setUserMenuOpen] = useState(false)
@@ -57,14 +58,20 @@ export function TopBar() {
     <>
       <header className="topbar flex items-center gap-4 border-b border-border bg-background px-4">
         {/* Logo area */}
-        <Link to="/" className="flex items-center gap-2.5 pr-4" style={{ width: 'calc(260px - 40px)' }}>
+        <Link
-          <div className="flex h-8 w-8 items-center justify-center rounded-lg bg-gradient-brand">
+          to="/"
+          className="flex items-center gap-2.5 pr-4 transition-all duration-200"
+          style={{ width: sidebarCollapsed ? '32px' : 'calc(260px - 40px)' }}
+        >
+          <div className="flex h-8 w-8 shrink-0 items-center justify-center rounded-lg bg-gradient-brand">
             <BrandLogo size="sm" className="h-4 w-4" />
           </div>
-          <span className="text-sm font-heading font-bold tracking-tight">
+          {!sidebarCollapsed && (
-            <span className="text-foreground">Resolution</span>
+            <span className="text-sm font-heading font-bold tracking-tight">
-            <span className="text-gradient-brand">Flow</span>
+              <span className="text-foreground">Resolution</span>
-          </span>
+              <span className="text-gradient-brand">Flow</span>
+            </span>
+          )}
         </Link>
 
         {/* Search trigger */}

frontend/src/components/workspace/WorkspaceCreateModal.tsx

@@ -0,0 +1,136 @@
+import { useState } from 'react'
+import { X, Loader2 } from 'lucide-react'
+import { workspacesApi } from '@/api/workspaces'
+import { useWorkspaceStore } from '@/store/workspaceStore'
+import { toast } from '@/lib/toast'
+import { cn } from '@/lib/utils'
+
+interface WorkspaceCreateModalProps {
+  open: boolean
+  onClose: () => void
+}
+
+const ICONS = ['📁', '🔧', '📋', '🚀', '🎯', '💼', '🔒', '📊', '🧪', '⚙️']
+
+export function WorkspaceCreateModal({ open, onClose }: WorkspaceCreateModalProps) {
+  const fetchWorkspaces = useWorkspaceStore(s => s.fetchWorkspaces)
+  const [name, setName] = useState('')
+  const [description, setDescription] = useState('')
+  const [icon, setIcon] = useState('📁')
+  const [saving, setSaving] = useState(false)
+
+  const slug = name
+    .toLowerCase()
+    .replace(/[^a-z0-9\s-]/g, '')
+    .replace(/\s+/g, '-')
+    .slice(0, 50)
+
+  const handleSubmit = async (e: React.FormEvent) => {
+    e.preventDefault()
+    if (!name.trim() || !slug) return
+    setSaving(true)
+    try {
+      await workspacesApi.create({ name: name.trim(), slug, description: description.trim() || undefined, icon })
+      await fetchWorkspaces()
+      toast.success(`Workspace "${name}" created`)
+      setName('')
+      setDescription('')
+      setIcon('📁')
+      onClose()
+    } catch (err: unknown) {
+      const message = err instanceof Error ? err.message : 'Failed to create workspace'
+      toast.error(message)
+    } finally {
+      setSaving(false)
+    }
+  }
+
+  if (!open) return null
+
+  return (
+    <div className="fixed inset-0 z-[100] flex items-center justify-center">
+      <div className="absolute inset-0 bg-black/60 backdrop-blur-sm animate-fade-in" onClick={onClose} />
+      <div className="relative w-full max-w-md rounded-xl border border-border bg-card p-6 shadow-2xl animate-scale-in">
+        <div className="flex items-center justify-between mb-5">
+          <h2 className="text-lg font-heading font-bold text-foreground">Create Workspace</h2>
+          <button onClick={onClose} className="rounded-lg p-1 text-muted-foreground hover:bg-accent hover:text-foreground">
+            <X size={18} />
+          </button>
+        </div>
+
+        <form onSubmit={handleSubmit} className="space-y-4">
+          {/* Icon picker */}
+          <div>
+            <label className="mb-1.5 block text-sm font-medium text-foreground">Icon</label>
+            <div className="flex flex-wrap gap-1.5">
+              {ICONS.map(i => (
+                <button
+                  key={i}
+                  type="button"
+                  onClick={() => setIcon(i)}
+                  className={cn(
+                    'flex h-9 w-9 items-center justify-center rounded-lg text-lg transition-colors',
+                    icon === i
+                      ? 'bg-primary/10 border border-primary/30'
+                      : 'border border-border hover:bg-accent'
+                  )}
+                >
+                  {i}
+                </button>
+              ))}
+            </div>
+          </div>
+
+          {/* Name */}
+          <div>
+            <label className="mb-1.5 block text-sm font-medium text-foreground">Name</label>
+            <input
+              type="text"
+              value={name}
+              onChange={e => setName(e.target.value)}
+              placeholder="e.g., Network Operations"
+              className="w-full rounded-lg border border-border bg-background px-3 py-2 text-sm text-foreground placeholder:text-muted-foreground focus:border-primary focus:outline-none focus:ring-1 focus:ring-primary/20"
+              autoFocus
+            />
+            {slug && (
+              <p className="mt-1 text-[0.6875rem] text-muted-foreground">
+                Slug: <code className="rounded bg-secondary px-1">{slug}</code>
+              </p>
+            )}
+          </div>
+
+          {/* Description */}
+          <div>
+            <label className="mb-1.5 block text-sm font-medium text-foreground">Description <span className="text-muted-foreground font-normal">(optional)</span></label>
+            <input
+              type="text"
+              value={description}
+              onChange={e => setDescription(e.target.value)}
+              placeholder="Brief description"
+              className="w-full rounded-lg border border-border bg-background px-3 py-2 text-sm text-foreground placeholder:text-muted-foreground focus:border-primary focus:outline-none focus:ring-1 focus:ring-primary/20"
+            />
+          </div>
+
+          {/* Actions */}
+          <div className="flex justify-end gap-2 pt-2">
+            <button
+              type="button"
+              onClick={onClose}
+              className="rounded-lg border border-border px-4 py-2 text-sm font-medium text-muted-foreground hover:bg-accent hover:text-foreground transition-colors"
+            >
+              Cancel
+            </button>
+            <button
+              type="submit"
+              disabled={!name.trim() || saving}
+              className="flex items-center gap-2 rounded-lg bg-gradient-brand px-4 py-2 text-sm font-semibold text-white shadow-lg shadow-primary/20 hover:opacity-90 transition-opacity disabled:opacity-50"
+            >
+              {saving && <Loader2 size={14} className="animate-spin" />}
+              Create
+            </button>
+          </div>
+        </form>
+      </div>
+    </div>
+  )
+}

frontend/src/components/workspace/WorkspaceSwitcher.tsx

@@ -1,6 +1,7 @@
 import { useState, useRef, useEffect } from 'react'
 import { ChevronDown, Plus } from 'lucide-react'
 import { useWorkspaceStore } from '@/store/workspaceStore'
+import { WorkspaceCreateModal } from './WorkspaceCreateModal'
 import { toast } from '@/lib/toast'
 import { cn } from '@/lib/utils'
 
@@ -9,6 +10,7 @@ export function WorkspaceSwitcher() {
   const activeWorkspace = workspaces.find(w => w.id === activeWorkspaceId)
 
   const [open, setOpen] = useState(false)
+  const [createModalOpen, setCreateModalOpen] = useState(false)
   const ref = useRef<HTMLDivElement>(null)
 
   useEffect(() => {
@@ -30,6 +32,7 @@ export function WorkspaceSwitcher() {
   if (!activeWorkspace) return null
 
   return (
+    <>
     <div className="relative px-3 py-2" ref={ref}>
       <button
         onClick={() => setOpen(!open)}
@@ -66,7 +69,10 @@ export function WorkspaceSwitcher() {
             ))}
           </div>
           <div className="border-t border-border p-1">
-            <button className="flex w-full items-center gap-2 rounded-md px-3 py-2 text-sm text-muted-foreground hover:bg-accent hover:text-foreground">
+            <button
+              onClick={() => { setOpen(false); setCreateModalOpen(true) }}
+              className="flex w-full items-center gap-2 rounded-md px-3 py-2 text-sm text-muted-foreground hover:bg-accent hover:text-foreground"
+            >
               <Plus size={14} />
               Add workspace…
             </button>
@@ -74,5 +80,8 @@ export function WorkspaceSwitcher() {
         </div>
       )}
     </div>
+
+    <WorkspaceCreateModal open={createModalOpen} onClose={() => setCreateModalOpen(false)} />
+    </>
   )
 }

frontend/src/index.css

@@ -76,6 +76,11 @@
   grid-template-rows: 56px 1fr;
   height: 100vh;
   overflow: hidden;
+  transition: grid-template-columns 200ms ease;
+}
+
+.app-shell--collapsed {
+  grid-template-columns: 56px 1fr;
 }
 
 .topbar {

frontend/src/pages/TreeLibraryPage.tsx

@@ -27,8 +27,10 @@ export function TreeLibraryPage() {
   const [trees, setTrees] = useState<TreeListItem[]>([])
   const [categories, setCategories] = useState<CategoryListItem[]>([])
   const [folders, setFolders] = useState<FolderListItem[]>([])
-  const [selectedCategoryId, setSelectedCategoryId] = useState<string>('')
+  const urlCategory = searchParams.get('category') || ''
-  const [selectedTags, setSelectedTags] = useState<string[]>([])
+  const urlTags = searchParams.get('tags')
+  const [selectedCategoryId, setSelectedCategoryId] = useState<string>(urlCategory)
+  const [selectedTags, setSelectedTags] = useState<string[]>(urlTags ? urlTags.split(',') : [])
   const [selectedFolderId, setSelectedFolderId] = useState<string | null>(null)
   const [searchQuery, setSearchQuery] = useState('')
   const [isLoading, setIsLoading] = useState(true)
@@ -40,7 +42,7 @@ export function TreeLibraryPage() {
     urlType === 'troubleshooting' || urlType === 'procedural' ? urlType : 'all'
   )
 
-  // Sync type filter when URL changes (e.g. clicking nav sub-items)
+  // Sync filters when URL changes (e.g. clicking sidebar categories/tags or nav sub-items)
   useEffect(() => {
     const t = searchParams.get('type')
     if (t === 'troubleshooting' || t === 'procedural') {
@@ -48,6 +50,9 @@ export function TreeLibraryPage() {
     } else {
       setTypeFilter('all')
     }
+    setSelectedCategoryId(searchParams.get('category') || '')
+    const tagsParam = searchParams.get('tags')
+    setSelectedTags(tagsParam ? tagsParam.split(',') : [])
   }, [searchParams])
 
   // View preferences from store

frontend/src/store/workspaceStore.ts

@@ -6,15 +6,18 @@ interface WorkspaceState {
   workspaces: Workspace[]
   activeWorkspaceId: string | null
   loading: boolean
+  sidebarCollapsed: boolean
   setActiveWorkspace: (id: string) => void
   fetchWorkspaces: () => Promise<void>
   getActiveWorkspace: () => Workspace | undefined
+  toggleSidebar: () => void
 }
 
 export const useWorkspaceStore = create<WorkspaceState>((set, get) => ({
   workspaces: [],
   activeWorkspaceId: localStorage.getItem('active-workspace-id'),
   loading: false,
+  sidebarCollapsed: localStorage.getItem('sidebar-collapsed') === 'true',
 
   setActiveWorkspace: (id: string) => {
     localStorage.setItem('active-workspace-id', id)
@@ -47,4 +50,10 @@ export const useWorkspaceStore = create<WorkspaceState>((set, get) => ({
     const { workspaces, activeWorkspaceId } = get()
     return workspaces.find(w => w.id === activeWorkspaceId)
   },
+
+  toggleSidebar: () => {
+    const next = !get().sidebarCollapsed
+    localStorage.setItem('sidebar-collapsed', String(next))
+    set({ sidebarCollapsed: next })
+  },
 }))