feat: persist resume metadata on SFTP single-file cancel

internal/protocol/sftp/sftp.go

@@ -725,6 +725,14 @@ func downloadSingleFile(ctx context.Context, c *client, req *core.DownloadReques
 	for {
 		select {
 		case <-ctx.Done():
+			// Persist partial progress so the user can resume later
+			// with --resume. Unconditional — mirrors the FTP and SFTP
+			// parallel paths that always save a .goget.meta sidecar on
+			// cancellation.
+			if outputPath != "" && outputPath != "-" && total > 0 {
+				meta := output.NewResumeMetadata(req.URL.String(), "", "", int64(total), totalSize)
+				_ = meta.Save(outputPath)
+			}
 			return nil, ctx.Err()
 		default:
 		}