diff --git a/src/brainy.ts b/src/brainy.ts
index 711d8d02..c479fcc3 100644
--- a/src/brainy.ts
+++ b/src/brainy.ts
@@ -16732,8 +16732,19 @@ export class Brainy<T = any> implements BrainyInterface<T> {
       if (legacyEntityPaths.length === 0) {
         // Already flat (root entities, no head-branch entities) → stamp the marker
         // so future opens short-circuit. A genuinely empty/fresh dir gets no marker.
-        const rootEntities = await probe.listRawObjects('entities')
-        if (rootEntities.length > 0) {
+        // "Are there any entities?" is answered by ONE directory read, not by a
+        // recursive listing of every file in the tree: this runs on the open path
+        // of every store that does not yet carry the marker (a restore, a store
+        // built by an older release), and on a large store that listing walks the
+        // whole canonical tree to learn a boolean.
+        const oneLevel = (
+          probe as unknown as { listRawPrefixes?: (prefix: string) => Promise<string[]> }
+        ).listRawPrefixes
+        const hasRootEntities =
+          typeof oneLevel === 'function'
+            ? (await oneLevel.call(probe, 'entities')).length > 0
+            : (await probe.listRawObjects('entities')).length > 0
+        if (hasRootEntities) {
           await probe.writeRawObject('_system/migration-layout.json', {
             layout: 'flat-v8',
             version: 8,