fix(launcher): remove orphaned client-in-game helpers

A launcher can exit while its long-lived close/hide helper remains. The next
run then starts another watcher, so several copies watch the same prefix.

Add an opt-in RCLOL_CLEAN_STALE_HELPERS=1 preflight that removes only helper
processes of this prefix reparented to init/systemd. Helpers of a live
launcher, other prefixes, the game, Riot/League/CEF, darlingserver and the
runtime are preserved. Unreadable or relative process data leaves a process
alone.

Validated across repeated launcher starts: the cleanup removed four, then one,
then one orphaned watcher; a subsequent dry run reported no orphaned helpers.
Zombie reaping after partial recovery is tracked separately in #124.

docs/SETUP.md

@@ -86,6 +86,15 @@ launchd/mldr, sockets and `.init.pid`; if X11/Xwayland cannot be inspected it
 does nothing. See
 [troubleshooting](TROUBLESHOOTING.md#client-remains-running-without-a-window).
 
+`RCLOL_CLEAN_STALE_HELPERS=1` runs a preflight before the match helper starts.
+It removes `close-league-client-in-game.py` and
+`hide-league-client-in-game.py` processes of this prefix whose parent is
+`init`/`systemd`, which means the launcher that started them has exited. A
+helper of a live launcher, another prefix, the game, Riot/League/CEF and
+`darlingserver` are preserved. It fails closed when a command line,
+environment, stat entry or parent cannot be read. See
+[troubleshooting](TROUBLESHOOTING.md#multiple-client-in-game-helpers).
+
 `RCLOL_FILTER_HOST_ENV=1` opts in to removing host desktop-session variables before
 the guest starts: `WAYLAND_DISPLAY`, `XDG_SESSION_*`, `XDG_CURRENT_DESKTOP`,
 GNOME/KDE/GDM, systemd, SSH agent, terminal, toolkit (`QT_*`, `GTK_*`, `GDK_*`),

docs/TROUBLESHOOTING.md

@@ -158,6 +158,30 @@ managed client window is visible. With X11/Xwayland unavailable it fails closed.
 This saves the Darling bootstrap but not the Riot Client/CEF startup itself. If
 no window appears afterward, use a full runtime shutdown/restart.
 
+### Multiple client-in-game helpers
+
+The close/hide helper is a long-lived watcher. If an earlier launcher exits
+while it remains, the next launch can start another copy; list them with:
+
+```sh
+pgrep -af 'close-league-client-in-game.py|hide-league-client-in-game.py'
+```
+
+To remove the orphaned copies before the next helper starts:
+
+```sh
+RCLOL_CLEAN_STALE_HELPERS=1 ./scripts/run.sh
+```
+
+Only helpers of the current prefix whose parent is `init`/`systemd` are
+terminated. Helpers whose launcher is still alive, other prefixes, the game,
+Riot/League/CEF, `darlingserver` and the runtime are never touched. A dry run
+is available from the configured tools directory:
+
+```sh
+RCLOL_CLEAN_STALE_HELPERS=1 python3 build/runtime/tools/clean-stale-helpers.py --dry-run
+```
+
 ### Client window stays black after a match
 
 The League client keeps its Chromium/CEF UI (`LeagueClientUx` and its helpers)