perf(files): breadcrumb no longer blocks the listing; ancestors cached

Every folder navigation awaited rebuildBreadCrumb() — one sequential
fetch per ancestor level — before requesting the first page, so a
depth-8 folder paid ~8 RTTs of dead time before the content even
started loading. And nothing was cached: navigating between sibling
folders re-fetched the same ancestors every time.

- filesModel: session cache id → FolderItem for breadcrumb resolution
  (warm navigations rebuild the trail with zero fetches), invalidated
  on rename/move (single + batch) via invalidateFolderMeta. The trail
  is now built locally and committed atomically, guarded by a
  generation token so a rebuild superseded by a faster follow-up
  navigation can no longer interleave writes into the newer trail.
- filesView.loadFiles: the rebuild runs concurrently with the first
  page fetch; crumbs, history and title update when it resolves.
  Navigation latency becomes max(listing, ancestor chain) instead of
  their sum — and ~equal to the listing alone once the cache is warm.
  The home-folder fallback for inaccessible targets is preserved by
  reloading the listing when the rebuild had to reset app.currentPath.

https://claude.ai/code/session_01Dp3oWon5GBMVn4j3QXZdgx

static/js/app/filesView.js

@@ -438,9 +438,17 @@ async function loadFiles(options = { insertHistory: true }) {
             }
         }
 
-        await rebuildBreadCrumb();
-        ui.updateBreadcrumb();
-        updateHistory(options.insertHistory ?? true);
+        // Rebuild the breadcrumb concurrently with the first page fetch —
+        // the listing does not depend on it, and awaiting the ancestor
+        // chain first added one round-trip per depth level before the
+        // content even started loading. Crumbs, history and title update
+        // when it resolves (skipped when superseded by a newer navigation).
+        const requestedPath = app.currentPath;
+        const breadcrumbReady = rebuildBreadCrumb().then((committed) => {
+            if (!committed) return;
+            ui.updateBreadcrumb();
+            updateHistory(options.insertHistory ?? true);
+        });
 
         clearTimeout(spinnerTimeout);
 
@@ -457,6 +465,17 @@ async function loadFiles(options = { insertHistory: true }) {
         // Hand off to _loadPage (re-use cursor/groupBy state just reset above).
         _loading = false; // _loadPage sets its own guard
         await _loadPage({ isFirstPage: true });
+        await breadcrumbReady;
+
+        // rebuildBreadCrumb falls back to the home folder when the
+        // requested folder is inaccessible (deleted / permission revoked).
+        // The old sequential flow got the home listing for free; reload to
+        // match it.
+        if (app.currentPath !== requestedPath) {
+            ui.resetFilesList();
+            _nextCursor = null;
+            await _loadPage({ isFirstPage: true });
+        }
 
         // Deep-link: open a specific file if requested via app.viewFile.
         // We don't have a flat file list anymore (cursor pages), so only try