diff --git a/rust/crates/mnote-web/browser/sidebar-tree-live-apply-runtime.js b/rust/crates/mnote-web/browser/sidebar-tree-live-apply-runtime.js
index e3378868..393837a7 100644
--- a/rust/crates/mnote-web/browser/sidebar-tree-live-apply-runtime.js
+++ b/rust/crates/mnote-web/browser/sidebar-tree-live-apply-runtime.js
@@ -21,6 +21,9 @@ export const createSidebarTreeLiveApplyRuntime = (dependencies = {}) => {
   var fileTreeLazyChildrenCache = new Map();
   var fileTreeExpandedRelativePaths = new Set();
   var fileTreeLazyCacheRootUri = '';
+  var fileTreeExpansionStorageRootUri = '';
+  var fileTreeExpansionRestoreTimer = 0;
+  var FILETREE_EXPANSION_STORAGE_KEY = 'mnote.localFileTree.expandedRelativePaths.v1';
 
   function updateTitleEverywhere(documentId, title) {
     if (!documentId) return;
@@ -616,19 +619,68 @@ export const createSidebarTreeLiveApplyRuntime = (dependencies = {}) => {
     fileTreeLazyCacheRootUri = rootUri;
     fileTreeLazyChildrenCache.clear();
     fileTreeExpandedRelativePaths.clear();
+    loadStoredFileTreeExpansionState(rootUri);
+  }
+
+  function storedFileTreeExpansionBuckets() {
+    try {
+      if (!window.sessionStorage) return {};
+      var parsed = JSON.parse(window.sessionStorage.getItem(FILETREE_EXPANSION_STORAGE_KEY) || '{}');
+      return parsed && typeof parsed === 'object' && !Array.isArray(parsed) ? parsed : {};
+    } catch (_) {
+      return {};
+    }
+  }
+
+  function loadStoredFileTreeExpansionState(rootUri) {
+    var normalizedRootUri = String(rootUri || '').trim();
+    if (!normalizedRootUri || fileTreeExpansionStorageRootUri === normalizedRootUri) return;
+    fileTreeExpansionStorageRootUri = normalizedRootUri;
+    var buckets = storedFileTreeExpansionBuckets();
+    var paths = Array.isArray(buckets[normalizedRootUri]) ? buckets[normalizedRootUri] : [];
+    paths.forEach(function(path) {
+      var normalized = String(path || '').trim();
+      if (normalized) fileTreeExpandedRelativePaths.add(normalized);
+    });
+  }
+
+  function persistFileTreeExpansionState() {
+    var rootUri = String(currentRootUri() || fileTreeLazyCacheRootUri || '').trim();
+    if (!rootUri) return;
+    try {
+      if (!window.sessionStorage) return;
+      var buckets = storedFileTreeExpansionBuckets();
+      buckets[rootUri] = Array.from(fileTreeExpandedRelativePaths)
+        .map(function(path) { return String(path || '').trim(); })
+        .filter(Boolean)
+        .slice(0, 256);
+      window.sessionStorage.setItem(FILETREE_EXPANSION_STORAGE_KEY, JSON.stringify(buckets));
+    } catch (_) {}
+  }
+
+  function scheduleRestorePersistedFileTreeExpansionState() {
+    if (fileTreeExpansionRestoreTimer) window.clearTimeout(fileTreeExpansionRestoreTimer);
+    fileTreeExpansionRestoreTimer = window.setTimeout(function() {
+      fileTreeExpansionRestoreTimer = 0;
+      restorePersistedFileTreeExpansionState();
+    }, 0);
   }
 
   function rememberFileTreeExpansionState() {
+    var changed = false;
     document.querySelectorAll('#sidebar-file-tree-root .tree-row[data-shell-mode="filetree"]').forEach(function(row) {
       if (!(row instanceof HTMLElement)) return;
       var relativePath = localFileTreeRelativePathFromRow(row);
       if (!relativePath) return;
       if (row.getAttribute('aria-expanded') === 'true') {
+        if (!fileTreeExpandedRelativePaths.has(relativePath)) changed = true;
         fileTreeExpandedRelativePaths.add(relativePath);
       } else {
+        if (fileTreeExpandedRelativePaths.has(relativePath)) changed = true;
         fileTreeExpandedRelativePaths.delete(relativePath);
       }
     });
+    if (changed) persistFileTreeExpansionState();
   }
 
   function renderFileProjection(projection) {
@@ -727,6 +779,8 @@ export const createSidebarTreeLiveApplyRuntime = (dependencies = {}) => {
     if (currentSourceKind() !== 'local_folder') return;
     var rootUri = currentRootUri();
     if (!rootUri) return;
+    ensureFileTreeLazyCacheScope();
+    scheduleRestorePersistedFileTreeExpansionState();
     var revision = '';
     var refreshTimer = 0;
     var scheduleRefresh = function() {
@@ -824,6 +878,7 @@ export const createSidebarTreeLiveApplyRuntime = (dependencies = {}) => {
     if (!relativePath) return;
     if (expanded) fileTreeExpandedRelativePaths.add(relativePath);
     else fileTreeExpandedRelativePaths.delete(relativePath);
+    persistFileTreeExpansionState();
   }
 
   function renderCachedFileTreeChildren(row, button, relativePath) {
@@ -896,6 +951,29 @@ export const createSidebarTreeLiveApplyRuntime = (dependencies = {}) => {
     setTreeRowExpanded(row, button, !collapsed);
   }
 
+  function restorePersistedFileTreeExpansionState() {
+    if (currentSourceKind() !== 'local_folder') return false;
+    ensureFileTreeLazyCacheScope();
+    if (!fileTreeExpandedRelativePaths.size) return false;
+    var restored = false;
+    document.querySelectorAll('#sidebar-file-tree-root .tree-row[data-shell-mode="filetree"]').forEach(function(row) {
+      if (!(row instanceof HTMLElement)) return;
+      if (String(row.getAttribute('data-row-kind') || '').trim() !== 'folder') return;
+      var relativePath = localFileTreeRelativePathFromRow(row);
+      if (!relativePath || !fileTreeExpandedRelativePaths.has(relativePath)) return;
+      var button = row.querySelector('[data-rust-action="toggle"]');
+      if (row.getAttribute('data-filetree-children-loaded') === 'true') {
+        setTreeRowExpanded(row, button, true);
+        restored = true;
+        return;
+      }
+      void loadFileTreeChildren(row, button);
+      restored = true;
+    });
+    if (restored) document.documentElement.setAttribute('data-mnote-filetree-expansion-restored', 'true');
+    return restored;
+  }
+
 
   function installTreeLiveApplyEventListeners() {
     window.addEventListener('tree:title-updated', function(event) {
@@ -1021,6 +1099,7 @@ export const createSidebarTreeLiveApplyRuntime = (dependencies = {}) => {
     refreshLocalFolderSidebarSnapshot,
     removeDocumentRowForMode,
     renderSidebarSnapshot,
+    restorePersistedFileTreeExpansionState,
     setTreeLiveApplyError,
     startLocalFolderSidebarWatch,
     toggleChildren,
diff --git a/rust/crates/mnote-web/src/routes/onlyoffice.rs b/rust/crates/mnote-web/src/routes/onlyoffice.rs
index 7e6faa0d..cb059e58 100644
--- a/rust/crates/mnote-web/src/routes/onlyoffice.rs
+++ b/rust/crates/mnote-web/src/routes/onlyoffice.rs
@@ -474,7 +474,16 @@ pub async fn page(Query(query): Query<OnlyOfficePageQuery>) -> Result<Response,
           url.host = origin.host;
           return url.toString();
         }}
+        const isLocalFolderFileOpen = url.pathname === "/api/local-folder/files/open";
         const isLocal = ["127.0.0.1", "localhost", "host.docker.internal"].includes(url.hostname);
+        if (proxyOrigin && isLocalFolderFileOpen) {{
+          const origin = new URL(proxyOrigin);
+          url.protocol = origin.protocol;
+          url.host = origin.host;
+          const proxy = new URL("/api/onlyoffice/proxy", proxyOrigin);
+          proxy.searchParams.set("u", base64UrlEncodeUtf8(url.toString()));
+          return proxy.toString();
+        }}
         if (proxyOrigin && (isLocal || url.searchParams.has("token"))) {{
           const proxy = new URL("/api/onlyoffice/proxy", proxyOrigin);
           proxy.searchParams.set("u", base64UrlEncodeUtf8(url.toString()));
@@ -1827,6 +1836,11 @@ mod tests {
         );
         assert!(html.contains("documentUrlBase,"));
         assert!(html.contains("resolvedFileUrl: fileState.resolvedFileUrl"));
+        assert!(html.contains(
+            r#"const isLocalFolderFileOpen = url.pathname === "/api/local-folder/files/open";"#
+        ));
+        assert!(html.contains("if (proxyOrigin && isLocalFolderFileOpen)"));
+        assert!(html.contains("if (proxyOrigin && (isLocal || url.searchParams.has(\"token\")))"));
     }
 
     fn test_state(legacy_next_base_url: Option<String>) -> AppState {