diff --git a/src/backend/drivers/139/driver.ts b/src/backend/drivers/139/driver.ts
index 70241b42..78f7e33c 100644
--- a/src/backend/drivers/139/driver.ts
+++ b/src/backend/drivers/139/driver.ts
@@ -50,7 +50,9 @@ export class Yun139Driver implements StorageDriver {
       if (foundFolder) {
         currentCatalogId = foundFolder.catalogID
       } else {
-        break
+        throw new Error(
+          `[139] folder not found: "${part}" in path "${physicalPath}"`,
+        )
       }
     }
 
diff --git a/src/backend/server/fs.ts b/src/backend/server/fs.ts
index ac90cef6..c35cb812 100644
--- a/src/backend/server/fs.ts
+++ b/src/backend/server/fs.ts
@@ -440,7 +440,9 @@ fsRouter.post("/list", async (c) => {
     // 对齐 Go 的路径级缓存策略；前端/上层可据此决定该目录的列表缓存时长。
     const cacheExpiration = storage
       ? resolveCacheExpiration(storage, reqPath)
-      : undefined
+      : 0 // Virtual directories must not be cached; a cached Virtual result
+          // would persist after the real storage comes online, causing the
+          // 'always shows root / Virtual provider' symptom for subsequent requests.
     return c.json({
       code: 200,
       message: "success",