Regression in SLR_soldier, SLR_sniper client beta with Flatpak: Unable to receive --assign-fd source 6: Bad file descriptor

[smcv]

Your system information

• Distribution: Flatpak, running on Arch
• What compatibility tool are you using?: SLR 1.0 (scout)
• What versions are listed in steamapps/common/SteamLinuxRuntime/VERSIONS.txt? (a prerelease)
• What versions are listed in steamapps/common/SteamLinuxRuntime_soldier/VERSIONS.txt? depot 0.20240104.72531, pressure-vessel 0.20240103.0
• What versions are listed in steamapps/common/SteamLinuxRuntime_sniper/VERSIONS.txt? (not directly applicable here)

Please describe your issue in as much detail as possible:

Games fail to launch with:

pressure-vessel-adverb[1331]: E: Unable to receive --assign-fd source 6: Bad file descriptor

This is a regression in the client_beta branch. Soldier version 0.20231211.70176 (pressure-vessel 0.20231208.0) was OK.

Corresponding versions of sniper have the same regression (flathub/com.valvesoftware.Steam#1235).

Steps for reproducing this issue:

1. Run STEAM_LINUX_RUNTIME_VERBOSE=1 flatpak run com.valvesoftware.Steam (not strictly necessary to reproduce but it will make diagnosis easier)
2. Opt in to client_beta branch of Steam Linux Runtime 2.0 (soldier)
3. Select Steam Linux Runtime 1.0 (scout) for a game (I used Tomb Raider)
4. Launch the game

[smcv]

This is fixed in today's new betas (labelled 0.20240125.x).

As far as I know, the stable branch was never affected.