Prebuild lookup structures to reduce UI lag on very large file lists.

frontend/src/components/UploadButton.vue

@@ -98,7 +98,7 @@ const uploadCloudFiles = (files: CloudFile[]) => {
   files.sort((a, b) => collator.compare(a.cloudName, b.cloudName))
   // Optimistic update: ghost folders and files
   const now = Math.floor(Date.now() / 1000)
-  const byPath = new Map(store.document.map(d => [d.loc ? `${d.loc}/${d.name}` : d.name, d]))
+  const byPath = store.docsByPath
   const added = new Set<string>()
   for (const f of files) {
     const lastSlash = f.cloudName.lastIndexOf('/')

frontend/src/stores/main.ts

@@ -269,6 +269,24 @@ export const useMainStore = defineStore('main', {
     sortOrder(): SortOrder { return this.query ? this.prefs.sortFiltered : this.prefs.sortListing },
     isUserLogged(): boolean { return this.user.isLoggedIn },
     recentDocuments(): Doc[] { return sorted(this.document, 'modified') },
+    /** Set of all full paths - for O(1) existence checks */
+    pathSet(): Set<string> {
+      return new Set(this.document.map(d => d.loc ? `${d.loc}/${d.name}` : d.name))
+    },
+    /** Map from location to documents in that folder - for O(1) folder listing */
+    docsByLoc(): Map<string, Doc[]> {
+      const map = new Map<string, Doc[]>()
+      for (const doc of this.document) {
+        const arr = map.get(doc.loc)
+        if (arr) arr.push(doc)
+        else map.set(doc.loc, [doc])
+      }
+      return map
+    },
+    /** Map from full path to Doc - for O(1) path lookup */
+    docsByPath(): Map<string, Doc> {
+      return new Map(this.document.map(d => [d.loc ? `${d.loc}/${d.name}` : d.name, d]))
+    },
     selectedFiles(): SelectedItems {
       const selected = this.selected
       const found = new Set<FUID>()

frontend/src/utils/fileutil.ts

@@ -3,8 +3,7 @@ import { useMainStore } from '@/stores/main'
 
 export const exists = (path: string[]) => {
   const store = useMainStore()
-  const p = path.join('/')
-  return store.document.some(doc => (doc.loc ? `${doc.loc}/${doc.name}` : doc.name) === p)
+  return store.pathSet.has(path.join('/'))
 }
 
 /** Strip file extension intelligently (handles .tar.gz, name.with.dots.pdf, etc.) */

frontend/src/views/ExplorerView.vue

@@ -51,7 +51,7 @@ const documents = computed(() => {
 
   // List the current location (no search)
   if (!query) return sorted(
-    store.document.filter(doc => doc.loc === loc),
+    store.docsByLoc.get(loc) ?? [],
     store.prefs.sortListing,
   )