Test doc: Steam Input steals the pad on 480; abort key; steam env baked in

Reproduced A/B on the dev box: with RP412STEAM=1 the wired pad
disappears from XInput because Steam Input intercepts Xbox controllers
for AppID 480. One-time client setting fixes it (disable Steam Input
for Spacewar, or globally for Xbox controllers); PadRIO hot-connects
within 3s once released. Our own AppID will configure this
server-side.

environ.ini in the dist now ships RP412STEAM=1 (the packer regenerates
the file, which was wiping the hand edit each round); machines without
Steam credentials fall back to TCP cleanly.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docs/STEAM-3-MACHINE-TEST.md

@@ -43,6 +43,29 @@ appid file is missing.
 6. Everyone lands back in the lobby room. A can launch again —
    different track, same lobby, no restarts.
 
+## Controllers: disable Steam Input (once per machine)
+
+Steam Input intercepts Xbox controllers for AppID 480 the moment the
+game initializes SteamAPI, hiding them from XInput entirely - the pad
+works everywhere else and is invisible only in-game (reproduced A/B on
+the dev box). Fix, either scope:
+
+- Per game: Steam Library -> Spacewar -> Properties -> Controller ->
+  Override for Spacewar: **Disable Steam Input**.
+- Global: Steam -> Settings -> Controller -> uncheck **Enable Steam
+  Input for Xbox controllers**.
+
+PadRIO re-probes every 3 seconds, so the pad hot-connects the moment
+Steam releases it - no restart needed. (Our own AppID will configure
+this server-side; test machines need the client setting.)
+
+## The abort key
+
+The ampersand key (Shift+7) is the arcade mission-abort. It ends YOUR
+mission on the spot - score banked, back to the lobby room. If the
+host presses it, the race ends for everyone (members return to the
+room too). Every "crash on keypress" so far has been this key.
+
 ## Notes and knowns
 
 - All pods use engine ports 1501/1502 by convention under Steam; the