feat: real recursive folder tree in the sidebar

The Folders section in the LeftSidebar previously rendered the flat
list of source roots — actual subdirectories were invisible. Now it
shows the full nested tree, click any node to filter, drop targets
work at every depth.

Backend
- New GET /folders/tree returning a list of root nodes (one per
  active SourceRoot). Each node is { id, name, path, photo_count,
  children: [...] } with children sorted alphabetically at every
  level. Walks Folder rows whose source_root_id matches and whose
  path is at or beneath the source root, then attaches them by
  parent path so partial scans don't break the tree.
- The source root's display label is overlaid on the root folder
  node so the top-level entry reads as "Library" instead of
  "/photos".
- list_photos folder_id filter now does descendant matching: when
  a Folder id is given, it includes the folder itself and every
  Folder whose path is a sep-prefixed descendant. Matches the
  Lightroom mental model: clicking "Library" or any parent folder
  shows everything beneath it. The existing source-root-id branch
  is unchanged.

Frontend
- New types/api.ts FolderTreeNode interface and sourceFolders.tree()
  helper.
- New hooks/useFolderTreeQuery.ts with a 30s staleTime and a
  findFolderInTree() walker for id-based name lookups.
- LeftSidebar drops the flat foldersData list and uses the tree
  query. folderNodeToTreeItem recursively maps backend nodes into
  the existing TreeItem shape; renderTreeItem already knew how to
  recurse into children, so the tree just works at any depth.
  Drop targets, drag-to-move, drag-to-copy, double-click rename,
  and active-state highlighting all carry over to nested folders.
- The renameMutation now also invalidates ['folders', 'tree'] so a
  source-root rename refreshes the tree label immediately.
- ActiveFilterChips switches to the tree query and uses the new
  findFolderInTree walker so the chip label resolves correctly for
  sub-folder filters too — not just top-level source roots.
- The "Scan all folders" button visibility now keys off the tree
  length instead of the flat folders length.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/app/routers/folders.py

@@ -44,6 +44,81 @@ async def get_folders(db: AsyncSession = Depends(get_db)):
     
     return {"folders": folders_list}
 
+@router.get("/tree")
+async def get_folder_tree(db: AsyncSession = Depends(get_db)):
+    """Recursive folder tree, one root per active SourceRoot. The tree
+    starts at the Folder row matching the SourceRoot.path (the scanner
+    creates one for every walked directory), with the SourceRoot's
+    display name overlaid so the top-level entry reads as "Library"
+    instead of "/photos".
+
+    Returns a list of root nodes; each node has:
+        { id, name, path, photo_count, children: [...] }
+
+    Sub-folders that physically belong to the same source root but
+    weren't created on disk (e.g. the / row the scanner sometimes
+    creates as a parent walk) are skipped via path-prefix filtering.
+    """
+    sr_result = await db.execute(
+        select(SourceRoot).where(SourceRoot.is_active == True)  # noqa: E712
+    )
+    source_roots = sr_result.scalars().all()
+
+    out = []
+    for sr in source_roots:
+        # Folders physically inside this source root, by path prefix.
+        prefix = os.path.normpath(sr.path).rstrip(os.sep)
+        f_result = await db.execute(
+            select(Folder).where(
+                Folder.source_root_id == sr.id,
+                # Either the folder IS the source root, or it sits beneath it.
+                (Folder.path == prefix) | (Folder.path.like(prefix + os.sep + '%'))
+            )
+        )
+        folders = f_result.scalars().all()
+        if not folders:
+            continue
+
+        # Build a path → node map so we can attach children regardless of
+        # parent_id consistency.
+        nodes = {
+            f.path: {
+                "id": f.id,
+                "name": f.name or os.path.basename(f.path),
+                "path": f.path,
+                "photo_count": f.photo_count or 0,
+                "children": [],
+            }
+            for f in folders
+        }
+
+        root_node = None
+        for f in folders:
+            node = nodes[f.path]
+            if f.path == prefix:
+                root_node = node
+                # Override the display name with the source root's label.
+                node["name"] = sr.name or node["name"]
+                continue
+            parent_path = os.path.normpath(os.path.dirname(f.path))
+            parent = nodes.get(parent_path)
+            if parent is not None:
+                parent["children"].append(node)
+            # If parent isn't in the set (orphan from a partial scan), drop
+            # the node — it can't be rendered consistently.
+
+        if root_node is not None:
+            # Sort children alphabetically at every level.
+            def sort_recursive(n):
+                n["children"].sort(key=lambda c: c["name"].lower())
+                for c in n["children"]:
+                    sort_recursive(c)
+            sort_recursive(root_node)
+            out.append(root_node)
+
+    return out
+
+
 @router.patch("/{folder_id}")
 async def rename_folder(
     folder_id: str,

backend/app/routers/photos.py

@@ -71,15 +71,17 @@ async def list_photos(
     if date_to:
         filters.append(Photo.taken_at <= date_to)
     
-    # Folder filter — the sidebar exposes "source roots" (top-level scan
+    # Folder filter. The sidebar can pass either a SourceRoot id or a
-    # paths) under the same UI affordance as folders, so the same param has
+    # Folder id; both should include descendants so clicking a parent
-    # to accept either a folder id or a source root id. If the value matches
+    # folder shows everything under it (Lightroom semantics).
-    # a source root, expand to every folder under that root and use IN.
     if folder_id:
         sr_check = await db.execute(
-            select(SourceRoot.id).where(SourceRoot.id == folder_id)
+            select(SourceRoot).where(SourceRoot.id == folder_id)
         )
-        if sr_check.scalar_one_or_none() is not None:
+        sr_row = sr_check.scalar_one_or_none()
+
+        if sr_row is not None:
+            # Source root → all folders under it (any depth).
             child_folders = await db.execute(
                 select(Folder.id).where(Folder.source_root_id == folder_id)
             )
@@ -87,11 +89,25 @@ async def list_photos(
             if child_ids:
                 filters.append(Photo.folder_id.in_(child_ids))
             else:
-                # Source root with no folder rows yet — match nothing rather
-                # than returning the entire library.
                 filters.append(Photo.id == '__no_match__')
         else:
-            filters.append(Photo.folder_id == folder_id)
+            # Folder id → that folder + every descendant by path prefix.
+            target_check = await db.execute(
+                select(Folder).where(Folder.id == folder_id)
+            )
+            target = target_check.scalar_one_or_none()
+            if target is None:
+                filters.append(Photo.id == '__no_match__')
+            else:
+                target_path = os.path.normpath(target.path).rstrip(os.sep)
+                desc_result = await db.execute(
+                    select(Folder.id).where(
+                        (Folder.path == target_path)
+                        | (Folder.path.like(target_path + os.sep + '%'))
+                    )
+                )
+                desc_ids = [row[0] for row in desc_result.all()]
+                filters.append(Photo.folder_id.in_(desc_ids))
     
     # Media type filter
     if media_type:

frontend/src/components/filter/ActiveFilterChips.tsx

@@ -1,21 +1,21 @@
 import { X } from 'lucide-react'
 import { useQuery } from '@tanstack/react-query'
 import { useFilterStore, hasActiveFilters } from '../../store/filterStore'
-import { sourceFolders, heaps as heapsApi, tags as tagsApi } from '../../services/api'
+import { sourceFolders, heaps as heapsApi, tags as tagsApi, type FolderTreeNode } from '../../services/api'
+import { findFolderInTree } from '../../hooks/useFolderTreeQuery'
 
 export function ActiveFilterChips() {
   const f = useFilterStore()
 
   // Look up names for id-based filters so the chips show something
-  // human-readable instead of opaque uuids.
+  // human-readable instead of opaque uuids. The folder tree handles
-  const { data: foldersData } = useQuery({
+  // both top-level source roots and nested subfolders.
-    queryKey: ['folders'],
+  const { data: folderTree } = useQuery<FolderTreeNode[]>({
-    queryFn: sourceFolders.list,
+    queryKey: ['folders', 'tree'],
+    queryFn: sourceFolders.tree,
     enabled: f.folderId !== null,
   })
-  const folder = f.folderId
+  const folder = f.folderId ? findFolderInTree(folderTree, f.folderId) : null
-    ? (foldersData?.folders ?? []).find((x: any) => x.id === f.folderId)
-    : null
 
   const { data: heaps = [] } = useQuery({
     queryKey: ['heaps'],
@@ -86,7 +86,7 @@ export function ActiveFilterChips() {
   if (f.folderId) {
     chips.push({
       key: 'folder',
-      label: `Folder: ${folder?.name || folder?.path?.split('/').pop() || f.folderId}`,
+      label: `Folder: ${folder?.name || f.folderId}`,
       onRemove: () => f.setFolderId(null),
     })
   }

frontend/src/components/layout/LeftSidebar.tsx

@@ -12,12 +12,13 @@ import {
   Copy,
 } from 'lucide-react'
 import clsx from 'clsx'
-import { sourceFolders, library, photos as photosApi } from '../../services/api'
+import { sourceFolders, library, photos as photosApi, type FolderTreeNode } from '../../services/api'
-import { useQuery, useMutation, useQueryClient } from '@tanstack/react-query'
+import { useMutation, useQueryClient } from '@tanstack/react-query'
 import { toast } from '../ToastContainer'
 import { useFilterStore } from '../../store/filterStore'
 import { HeapsPanel } from '../heaps/HeapsPanel'
 import { PHOTO_DRAG_MIME } from '../timeline/PhotoThumbnail'
+import { useFolderTreeQuery } from '../../hooks/useFolderTreeQuery'
 
 interface TreeItem {
   id: string
@@ -148,17 +149,15 @@ export function LeftSidebar() {
     }
   }
   
-  // Fetch folders from API
+  // Fetch the recursive folder tree (one root per active source root).
-  const { data: foldersData } = useQuery({
+  const { data: folderTree = [] } = useFolderTreeQuery()
-    queryKey: ['folders'],
-    queryFn: sourceFolders.list,
-  })
 
   const renameMutation = useMutation({
     mutationFn: ({ id, name }: { id: string; name: string }) =>
       sourceFolders.rename(id, name),
     onSuccess: () => {
       queryClient.invalidateQueries({ queryKey: ['folders'] })
+      queryClient.invalidateQueries({ queryKey: ['folders', 'tree'] })
     },
     onError: (e: any) =>
       toast.error('Rename failed', e?.response?.data?.detail || e.message || 'Unknown error'),
@@ -198,6 +197,18 @@ export function LeftSidebar() {
     setExpandedItems(newExpanded)
   }
   
+  // Recursively map a backend FolderTreeNode into our generic TreeItem.
+  const folderNodeToTreeItem = (node: FolderTreeNode): TreeItem => ({
+    id: `folder-${node.id}`,
+    label: node.name,
+    icon: <Folder className="h-4 w-4" />,
+    count: node.photo_count,
+    type: 'folder',
+    children: node.children.length > 0
+      ? node.children.map(folderNodeToTreeItem)
+      : undefined,
+  })
+
   const libraryTree: TreeItem[] = [
     {
       id: 'library',
@@ -214,13 +225,7 @@ export function LeftSidebar() {
       id: 'folders',
       label: 'Folders',
       icon: <Folder className="h-4 w-4" />,
-      children: foldersData?.folders?.map((folder: any) => ({
+      children: folderTree.map(folderNodeToTreeItem),
-        id: `folder-${folder.id}`,
-        label: folder.name || folder.path.split('/').pop() || folder.path,
-        icon: <Folder className="h-4 w-4" />,
-        count: folder.photo_count,
-        type: 'folder',
-      })) || [],
     },
   ]
   
@@ -411,7 +416,7 @@ export function LeftSidebar() {
       </div>
       
       {/* Bottom Actions */}
-      {foldersData?.folders?.length > 0 && (
+      {folderTree.length > 0 && (
         <div className="border-t border-border p-3">
           <button
             onClick={handleScanAll}

frontend/src/hooks/useFolderTreeQuery.ts

@@ -0,0 +1,26 @@
+import { useQuery } from '@tanstack/react-query'
+import { sourceFolders, type FolderTreeNode } from '../services/api'
+
+export const FOLDER_TREE_QUERY_KEY = ['folders', 'tree'] as const
+
+export function useFolderTreeQuery() {
+  return useQuery<FolderTreeNode[]>({
+    queryKey: FOLDER_TREE_QUERY_KEY,
+    queryFn: sourceFolders.tree,
+    staleTime: 30_000,
+  })
+}
+
+/** Walk the tree to find a node by id. Used for chip name lookups. */
+export function findFolderInTree(
+  tree: FolderTreeNode[] | undefined,
+  id: string
+): FolderTreeNode | null {
+  if (!tree) return null
+  for (const node of tree) {
+    if (node.id === id) return node
+    const child = findFolderInTree(node.children, id)
+    if (child) return child
+  }
+  return null
+}

frontend/src/services/api.ts

@@ -12,12 +12,26 @@ const api = axios.create({
 // Source Folders API. Source roots are config-driven now (PHOTO_DIRS in
 // .env → bootstrap on backend startup), so the UI only reads them and
 // optionally renames the display label.
+export interface FolderTreeNode {
+  id: string
+  name: string
+  path: string
+  photo_count: number
+  children: FolderTreeNode[]
+}
+
 export const sourceFolders = {
   list: async () => {
     const response = await api.get('/folders')
     return response.data
   },
 
+  /** Recursive folder tree, one root per active source root. */
+  tree: async (): Promise<FolderTreeNode[]> => {
+    const response = await api.get('/folders/tree')
+    return response.data
+  },
+
   scan: async (folderId: string) => {
     const response = await api.post(`/folders/${folderId}/scan`)
     return response.data