add saf directory display fix

mobile/services/safWalk.ts

@@ -0,0 +1,69 @@
+import type {
+  DirectoryEntry,
+  Folder,
+  FolderInfo,
+  PickDirectoryOptions,
+} from './safDirectory.types';
+
+export async function yieldToMainThread(): Promise<void> {
+  await new Promise<void>((resolve) => setTimeout(resolve, 0));
+}
+
+export const DEFAULT_WALK_BUDGET_MS = 16;
+
+export type SafWalkImpl = {
+  list: (uri: string) => DirectoryEntry[];
+  info: (uri: string) => FolderInfo;
+  yield: () => Promise<void>;
+};
+
+let walkImpl: SafWalkImpl | null = null;
+
+export function __setSafWalkImpl(impl: SafWalkImpl): void {
+  walkImpl = impl;
+}
+
+export function __setSafWalkForTests(impl: Partial<SafWalkImpl>): () => void {
+  const previous = walkImpl;
+  walkImpl = { ...previous, ...impl } as SafWalkImpl;
+  return () => {
+    walkImpl = previous;
+  };
+}
+
+export async function listFoldersChunked(
+  directoryUri: string,
+  options: PickDirectoryOptions = {},
+  budgetMs = DEFAULT_WALK_BUDGET_MS,
+): Promise<Folder[]> {
+  const impl = walkImpl;
+  if (!impl) throw new Error('SafWalkImpl not configured');
+
+  const { recursive = false, includeRoot = false } = options;
+  const result: Folder[] = [];
+  if (includeRoot) {
+    result.push({ ...impl.info(directoryUri), isDirectory: true });
+  }
+  if (!recursive) {
+    for (const entry of impl.list(directoryUri)) {
+      if (entry.isDirectory) result.push(entry);
+    }
+    return result;
+  }
+
+  let lastYield = Date.now();
+  const visit = async (uri: string) => {
+    if (Date.now() - lastYield >= budgetMs) {
+      lastYield = Date.now();
+      await impl.yield();
+    }
+    for (const entry of impl.list(uri)) {
+      if (entry.isDirectory) {
+        result.push(entry);
+        await visit(entry.uri);
+      }
+    }
+  };
+  await visit(directoryUri);
+  return result;
+}