diff --git a/frontend/src/components/heaps/HeapsPanel.tsx b/frontend/src/components/heaps/HeapsPanel.tsx
index a4a4b08..32e70d2 100644
--- a/frontend/src/components/heaps/HeapsPanel.tsx
+++ b/frontend/src/components/heaps/HeapsPanel.tsx
@@ -44,13 +44,27 @@ import {
  *  - filter heapId: which heap is currently filtered to (visual)
  *  - heap.is_active: which heap T adds to (server-side, single per row)
  */
-export function HeapsPanel() {
+interface HeapsPanelProps {
+  /** Controlled expand state. When both props are supplied the panel
+   *  defers to the parent for collapse/expand, so the sidebar's pane
+   *  sizing layer can flex the Heaps pane only when it is open. */
+  expanded?: boolean
+  onExpandedChange?: (expanded: boolean) => void
+}
+
+export function HeapsPanel({ expanded: expandedProp, onExpandedChange }: HeapsPanelProps = {}) {
   const { data: heaps = [] } = useHeapsQuery()
   const navigateToSection = useFilterStore((s) => s.navigateToSection)
   const currentSection = useFilterStore((s) => s.currentSection)
   const queryClient = useQueryClient()
 
-  const [expanded, setExpanded] = useState(true)
+  const [expandedInternal, setExpandedInternal] = useState(true)
+  const expanded = expandedProp ?? expandedInternal
+  const setExpanded = (next: boolean | ((prev: boolean) => boolean)) => {
+    const resolved = typeof next === 'function' ? (next as (p: boolean) => boolean)(expanded) : next
+    if (onExpandedChange) onExpandedChange(resolved)
+    else setExpandedInternal(resolved)
+  }
   const [creating, setCreating] = useState(false)
   const [newName, setNewName] = useState('')
   // Which heap row is currently being hovered with a drag — used to render
@@ -174,13 +188,23 @@ export function HeapsPanel() {
 
   return (
     <div>
-      {/* Section header — eyebrow style to match the LeftSidebar
-       *  library/folders headers. */}
+      {/* Section header — mirrors the Folders section eyebrow in
+       *  LeftSidebar so Heaps sits alongside it at the same visual
+       *  tier, with heap rows indented the same as folder rows. */}
       <div
         className="group mt-2 flex cursor-pointer items-center gap-1 px-3 py-1 text-[10px] font-semibold uppercase tracking-[0.14em] text-text-muted hover:text-text"
         onClick={() => setExpanded((v) => !v)}
+        aria-expanded={expanded}
+        role="button"
       >
-        <button className="rounded p-0.5 hover:bg-surface-offset">
+        <button
+          className="rounded p-0.5 hover:bg-surface-offset"
+          onClick={(e) => {
+            e.stopPropagation()
+            setExpanded((v) => !v)
+          }}
+          aria-label="Toggle heaps"
+        >
           {expanded ? (
             <ChevronDown className="h-3 w-3" />
           ) : (
@@ -209,6 +233,7 @@ export function HeapsPanel() {
               className="flex items-center gap-1 px-2 py-0.5"
               style={{ paddingLeft: '20px' }}
             >
+              <div className="h-4 w-4 flex-shrink-0" aria-hidden="true" />
               <Input
                 autoFocus
                 type="text"
@@ -237,10 +262,11 @@ export function HeapsPanel() {
 
           {heaps.length === 0 && !creating && (
             <div
-              className="px-2 py-0.5 text-[11px] text-text-faint"
+              className="flex items-center gap-1 px-2 py-0.5 text-[11px] text-text-faint"
               style={{ paddingLeft: '20px' }}
             >
-              No heaps yet
+              <div className="h-4 w-4 flex-shrink-0" aria-hidden="true" />
+              <span>No heaps yet</span>
             </div>
           )}
 
@@ -308,6 +334,10 @@ export function HeapsPanel() {
                   }
                 }}
               >
+                {/* Chevron-slot spacer — heap rows don't expand, but this
+                 *  reserves the same width that leaf folder rows use so
+                 *  icons and labels line up across the two hierarchies. */}
+                <div className="h-4 w-4 flex-shrink-0" aria-hidden="true" />
                 <ShoppingBasket
                   className={cn(
                     'h-3.5 w-3.5 flex-shrink-0',
diff --git a/frontend/src/components/layout/LeftSidebar.tsx b/frontend/src/components/layout/LeftSidebar.tsx
index 10bd7fc..17cf3d4 100644
--- a/frontend/src/components/layout/LeftSidebar.tsx
+++ b/frontend/src/components/layout/LeftSidebar.tsx
@@ -25,7 +25,6 @@ import {
   Clock,
   Upload as UploadIcon,
   Download as DownloadIcon,
-  CalendarRange,
 } from 'lucide-react'
 import { DateRangePicker } from '../filter/DateRangePicker'
 import { cn } from '@/lib/utils'
@@ -83,6 +82,9 @@ export function LeftSidebar() {
   const { user, isAdmin, logout } = useAuth()
   const scanActivity = useScanActivity()
   const [expandedItems, setExpandedItems] = useState<Set<string>>(new Set(['library', 'folders', 'heaps']))
+  // Library pane collapse. Its body holds Views, Folders, Shared, and
+  // Heaps, so a single toggle hides the whole navigation area.
+  const [libraryPaneOpen, setLibraryPaneOpen] = useState(true)
   // Inline rename state for source-root rows. Stores the id being edited
   // and the draft name. Double-click a folder row to start.
   const [renamingId, setRenamingId] = useState<string | null>(null)
@@ -836,15 +838,40 @@ export function LeftSidebar() {
 
   return (
     <div className="flex h-full flex-col bg-surface">
-      {/* Header with collapse button. Matches the right sidebar header
-       *  so both panels have symmetric affordances. */}
-      <div className="flex h-9 flex-shrink-0 items-center justify-between border-b border-border px-3">
-        <h2 className="text-[11px] font-semibold uppercase tracking-[0.14em] text-text-muted">
-          Library
-        </h2>
-        <div className="flex items-center gap-1">
+      {/* Active heap card — pinned at the very top so it stays visible
+       *  even when the date filter is expanded into a tall calendar.
+       *  Returns null when no heap is active, so the layout collapses
+       *  cleanly. */}
+      <ActiveHeapCard />
+
+      {/* Date range filter — always visible, collapsible. Drives the
+       *  global dateFrom/dateTo on the filter store, so it applies to
+       *  every section regardless of which tree item is selected. */}
+      <DateFilterSection />
+
+      {/* Resizable two-pane region: Library (Views + Folders + Shared)
+       *  on top, Heaps on the bottom. Each pane collapses to its
+       *  header; when both are expanded a drag divider splits the
+       *  vertical space between them (persisted to localStorage). */}
+      {/* Library pane — the sole navigation section. Contains Views,
+       *  Folders, Shared-with-me, and Heaps in a single scroll area;
+       *  collapses to its header when hidden. */}
+      <div
+        className="flex min-h-0 flex-col"
+        style={{ flex: libraryPaneOpen ? '1 1 0' : '0 0 auto' }}
+      >
+        <div
+          className="group flex h-9 flex-shrink-0 cursor-pointer items-center gap-2 border-b border-border px-3 text-[11px] font-semibold uppercase tracking-[0.14em] text-text-muted hover:text-text"
+          onClick={() => setLibraryPaneOpen((v) => !v)}
+          aria-expanded={libraryPaneOpen}
+          role="button"
+        >
+          <span className="flex-1 truncate">Library</span>
           <button
-            onClick={() => setUploadTarget({ open: true, folderId: null })}
+            onClick={(e) => {
+              e.stopPropagation()
+              setUploadTarget({ open: true, folderId: null })
+            }}
             className="rounded p-0.5 text-text-muted hover:bg-surface-2 hover:text-text"
             title="Upload photos"
             aria-label="Upload photos"
@@ -852,68 +879,61 @@ export function LeftSidebar() {
             <UploadIcon className="h-3.5 w-3.5" />
           </button>
         </div>
-      </div>
-      {/* Date range filter — always visible, collapsible. Drives the
-       *  global dateFrom/dateTo on the filter store, so it applies to
-       *  every section regardless of which tree item is selected. */}
-      <DateFilterSection />
+        {libraryPaneOpen && (
+          <div className="min-h-0 flex-1 overflow-y-auto pb-2">
+            {libraryTree.map((item) => renderTreeItem(item))}
 
-      {/* Active heap card — pinned just below the Library header so
-       *  toasts (bottom-left fixed) can't cover it. Returns null when
-       *  no heap is active, so the layout collapses cleanly. */}
-      <ActiveHeapCard />
-
-      {/* Tree View */}
-      <div className="flex-1 overflow-y-auto pb-2">
-        {libraryTree.map((item) => renderTreeItem(item))}
-
-        {/* Shared with me — folders shared by other users */}
-        {sharedFolders.length > 0 && (
-          <div className="mt-1">
-            <div className="px-3 py-1 text-[10px] font-semibold uppercase tracking-[0.14em] text-text-muted">
-              Shared with me
-            </div>
-            {sharedFolders.map((sf) => {
-              const isSelected = currentSection === `folder-${sf.id}`
-              return (
-                <div
-                  key={sf.id}
-                  className={cn(
-                    'flex h-[24px] cursor-pointer items-center gap-1 rounded px-2 text-[12px] leading-none',
-                    isSelected ? 'bg-primary/20 text-primary' : 'text-text hover:bg-surface-2',
-                  )}
-                  style={{ paddingLeft: '20px' }}
-                  onClick={() =>
-                    navigateToSection(`folder-${sf.id}`, { folderId: sf.id })
-                  }
-                >
-                  <Users
-                    className={cn(
-                      'h-3.5 w-3.5 flex-shrink-0',
-                      isSelected ? 'text-primary' : 'text-text-muted'
-                    )}
-                  />
-                  <span className="truncate" title={sf.name}>
-                    {sf.name}
-                  </span>
-                  <span className="ml-0.5 truncate text-[10px] text-text-faint">
-                    {sf.owner_username}
-                  </span>
-                  <span className="ml-auto rounded bg-surface-offset px-1 text-[9px] uppercase text-text-faint">
-                    {sf.permission}
-                  </span>
-                  {sf.photo_count > 0 && (
-                    <span className="flex h-4 min-w-[20px] flex-shrink-0 items-center justify-center rounded bg-surface-offset px-1 text-[10px] tabular-nums text-text-muted">
-                      {sf.photo_count}
-                    </span>
-                  )}
+            {/* Shared with me — folders shared by other users */}
+            {sharedFolders.length > 0 && (
+              <div className="mt-1">
+                <div className="px-3 py-1 text-[10px] font-semibold uppercase tracking-[0.14em] text-text-muted">
+                  Shared with me
                 </div>
-              )
-            })}
+                {sharedFolders.map((sf) => {
+                  const isSelected = currentSection === `folder-${sf.id}`
+                  return (
+                    <div
+                      key={sf.id}
+                      className={cn(
+                        'flex h-[24px] cursor-pointer items-center gap-1 rounded px-2 text-[12px] leading-none',
+                        isSelected ? 'bg-primary/20 text-primary' : 'text-text hover:bg-surface-2',
+                      )}
+                      style={{ paddingLeft: '20px' }}
+                      onClick={() =>
+                        navigateToSection(`folder-${sf.id}`, { folderId: sf.id })
+                      }
+                    >
+                      <Users
+                        className={cn(
+                          'h-3.5 w-3.5 flex-shrink-0',
+                          isSelected ? 'text-primary' : 'text-text-muted'
+                        )}
+                      />
+                      <span className="truncate" title={sf.name}>
+                        {sf.name}
+                      </span>
+                      <span className="ml-0.5 truncate text-[10px] text-text-faint">
+                        {sf.owner_username}
+                      </span>
+                      <span className="ml-auto rounded bg-surface-offset px-1 text-[9px] uppercase text-text-faint">
+                        {sf.permission}
+                      </span>
+                      {sf.photo_count > 0 && (
+                        <span className="flex h-4 min-w-[20px] flex-shrink-0 items-center justify-center rounded bg-surface-offset px-1 text-[10px] tabular-nums text-text-muted">
+                          {sf.photo_count}
+                        </span>
+                      )}
+                    </div>
+                  )
+                })}
+              </div>
+            )}
+
+            {/* Heaps — nested inside the Library section; HeapsPanel owns
+             *  its own eyebrow header + collapse state. */}
+            <HeapsPanel />
           </div>
         )}
-
-        <HeapsPanel />
       </div>
 
       {/* Bottom panel — user identity + settings, pinned below the tree. */}
@@ -1016,25 +1036,24 @@ function DateFilterSection() {
       : `${dateFrom ?? '…'} → ${dateTo ?? '…'}`
     : 'Any date'
   return (
-    <div className="flex-shrink-0 border-b border-border">
-      <button
+    <div className="flex-shrink-0">
+      <div
         onClick={() => setOpen((v) => !v)}
-        className="flex w-full items-center gap-2 px-3 py-2 text-left text-xs text-text-muted hover:bg-surface-2"
+        className="group flex h-9 cursor-pointer items-center gap-2 border-b border-border px-3 text-[11px] font-semibold uppercase tracking-[0.14em] text-text-muted hover:text-text"
         aria-expanded={open}
+        role="button"
       >
-        <CalendarRange className="h-3.5 w-3.5 shrink-0" />
-        <span className="truncate">{summary}</span>
-        <span
-          className={cn(
-            'ml-auto shrink-0 text-[10px] uppercase tracking-wider',
-            active && 'text-primary',
-          )}
-        >
-          {open ? 'Hide' : active ? 'Filtering' : 'Filter'}
+        <span className="flex-1 truncate">
+          {active ? summary : 'Date'}
         </span>
-      </button>
+        {active && (
+          <span className="rounded bg-primary/20 px-1 py-px text-[9px] uppercase tracking-wider text-primary">
+            Filtering
+          </span>
+        )}
+      </div>
       {open && (
-        <div className="px-3 pb-3">
+        <div className="border-b border-border px-3 py-3">
           <DateRangePicker
             from={dateFrom}
             to={dateTo}