Fixed multiple clients bug in umu.

ptlinux/cli.py

@@ -819,6 +819,7 @@ def _play_locked(
 			runner,
 			start_option=start_option,
 			use_gamebox=not no_box,
+			concurrent_prefix_launch=reuse_prepared,
 		)
 	except KeyboardInterrupt:
 		current_game_log = _current_game_log(

ptlinux/runtime.py

@@ -380,6 +380,7 @@ def run_game(
 	*,
 	start_option: DepotStartOption = DEFAULT_DEPOT_START_OPTION,
 	use_gamebox: bool = True,
+	concurrent_prefix_launch: bool = False,
 	timeout_seconds: float = 12 * 60 * 60,
 	check: bool = True,
 	extra_environment: Mapping[str, str] | None = None,
@@ -428,6 +429,13 @@ def run_game(
 			selection,
 			synchronization=resolve_proton_sync_mode(settings.proton_sync),
 		)
+	if selection.kind in {"umu", "proton7-container"}:
+		# Keep every UMU launch identical except for the verb, as required when
+		# several games share one prefix. The first client owns prefix startup;
+		# every later shared-lease client joins the active wineserver directly.
+		environment["PROTON_VERB"] = (
+			"runinprefix" if concurrent_prefix_launch else "waitforexitandrun"
+		)
 	if use_gamebox:
 		game_command = build_gamebox_command(game_command, settings)
 	if extra_environment: