Upload FastSeekWpf/Core/CacheManager.cs

FastSeekWpf/Core/CacheManager.cs

@@ -48,7 +48,14 @@ public static class CacheManager
             byte[] compressed = File.ReadAllBytes(CachePath);
             byte[] bytes = LZ4Pickler.Unpickle(compressed);
             string json = Encoding.UTF8.GetString(bytes);
-            return JsonSerializer.Deserialize<CacheData>(json, JsonOptions);
+            var cache = JsonSerializer.Deserialize<CacheData>(json, JsonOptions);
+            // Back-compat: single DriveRoot → DriveRoots list
+            if (cache != null && cache.DriveRoots == null || cache!.DriveRoots.Count == 0)
+            {
+                // This is the old format — can't use it, need full rescan
+                return null;
+            }
+            return cache;
         }
         catch
         {