Does this work?

LightlessSyncServer/LightlessSyncStaticFilesServer/Services/CachedFileProvider.cs

@@ -219,4 +219,27 @@ public sealed class CachedFileProvider : IDisposable
     {
         return hashes.Exists(_currentTransfers.Keys.Contains);
     }
+
+    public FileInfo? TryGetLocalFileInfo(string hash)
+    {
+        var fi = FilePathUtil.GetFileInfoForHash(_hotStoragePath, hash);
+        if (fi != null)
+        {
+            return GetLocalFilePath(hash);
+        }
+
+        _ = Task.Run(async () =>
+        {
+            try
+            {
+                await DownloadFileWhenRequired(hash).ConfigureAwait(false);
+            }
+            catch (Exception ex)
+            {
+                _logger.LogWarning(ex, "Download failed for {hash}", hash);
+            }
+        });
+
+        return null;
+    }
 }