Launcher: drop Steam's overlay from LD_PRELOAD

Launched from the Steam library, Steam preloads gameoverlayrenderer.so,
which segfaults Chromium's zygote; the GPU process can't start and
Chromium quits after about 30 seconds. Found testing on a Steam Frame;
reviewed by GPT-6 Astra.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

docs/technical-notes.md

@@ -85,6 +85,15 @@ the shortcut through the Steam client's DevTools port (`127.0.0.1:8080`,
 page `SharedJSContext`) with `SteamClient.Apps.AddShortcut`, so Steam doesn't
 need restarting. (`steam steam://addnonsteamgame/<path>` adds nothing.)
 
+Steam preloads its in-game overlay, `gameoverlayrenderer.so`, into everything
+it launches through `LD_PRELOAD`. In Chromium it segfaults the zygote during
+library initialisation. The GPU process then fails to launch
+(`GPU process launch failed: error_code=1002`), and after a few tries
+Chromium quits with `GPU process isn't usable. Goodbye.` about 30 seconds
+after starting. The `chromium-xr` launcher removes the overlay from
+`LD_PRELOAD` before starting Chromium, keeping anything else that was
+preloaded.
+
 ## Debugging
 
 - `chromium-xr --remote-debugging-port=9223 URL` opens DevTools on the Frame's

frame/chromium-xr

@@ -7,6 +7,27 @@ set -euo pipefail
 CHROME="${CHROMIUM_XR_HOME:-$HOME/chromium-xr}/chrome"
 [[ -x "$CHROME" ]] || { echo "chromium-xr: no build at $CHROME (run frame/install.sh)" >&2; exit 1; }
 
+# Steam preloads its in-game overlay (gameoverlayrenderer.so) into anything it
+# launches. It segfaults in Chromium's zygote, the GPU process then can't
+# start, and Chromium quits with "GPU process isn't usable". Drop it and keep
+# anything else that was preloaded.
+if [[ -n "${LD_PRELOAD:-}" ]]; then
+  keep=()
+  # Split on spaces and colons only, like ld.so, with no glob expansion.
+  # read -d '' takes the whole value, newlines included (it returns 1 at EOF).
+  IFS=' :' read -r -d '' -a libs < <(printf '%s' "$LD_PRELOAD") || true
+  for lib in ${libs[@]+"${libs[@]}"}; do
+    [[ -z "$lib" || "$lib" == *gameoverlayrenderer.so ]] || keep+=("$lib")
+  done
+  if (( ${#keep[@]} )); then
+    LD_PRELOAD=${keep[0]}
+    for lib in "${keep[@]:1}"; do LD_PRELOAD+=":$lib"; done
+    export LD_PRELOAD
+  else
+    unset LD_PRELOAD
+  fi
+fi
+
 # --enable-features=OpenXR: the Linux OpenXR device is off by default.
 # --ozone-platform=x11: gamescope's X display, where each app is a panel.
 # --no-first-run and --password-store=basic: otherwise startup can stop at a