Your system information

• Steam client version (build number or date): 1785187029
• Distribution (e.g. Ubuntu): Nobara Linux (KDE Plasma Desktop), Fedora-based
• Opted into Steam client beta?: No
• Have you checked for system updates?: Yes
• Steam Logs:

steam-logs-minimal.tar.gz

• GPU: AMD (Ryzen 7 4800HS integrated Radeon Graphics / Vega 7, RADV RENOIR, driver radv 26.1.5)

Please describe your issue in as much detail as possible:

Expected: Steam Linux Runtime 4.0 (AppID 4183110) installs normally through the Steam client and stays installed, so that Proton builds depending on it (Proton Experimental, Proton 11.0, Proton-GE Latest) can launch games normally.

Actual: Steam Linux Runtime 4.0 cannot be reliably installed or kept installed through the normal Steam client UI. It gets stuck showing as "installed" in the Library → Tools view (white/enabled text, greyed-out/unclickable Install button, no Install option in the right-click context menu — visually identical to the other correctly-installed runtimes) while the app's .acf manifest shows SizeOnDisk: 0, BytesDownloaded: 0, and an empty InstalledDepots block. On disk, the install folder (steamapps/common/SteamLinuxRuntime_4/) exists but its subfolders (pressure-vessel, pressure-vessel-arm64, steamrt4_platform_*) are 0 bytes, and there is no toolmanifest.vdf — the install never actually completes.

Any Proton build that depends on AppID 4183110 (Proton Experimental, Proton 11.0, Proton-GE Latest) then fails to launch — either silently (process exits ~1 second after clicking Play, button just reverts to "Play" with no message) or with a "Compatibility tool failed" popup. compat_log.txt shows:

Failed to load manifest for tool 4183110!
...
Tool 4183110 "Steam Linux Runtime 4.0" unsupported version 0.
Tool <proton_appid> "<Proton build>" has a dependency on tool 4183110: dependent tool cmdline wrap failed.

Proton builds that do not depend on AppID 4183110 (Proton 9.0-4, Proton 10.0-4, which depend on Steam Linux Runtime 3.0 "sniper" / AppID 1628350 instead) launch the exact same games without any issue, same shortcuts, same launch options otherwise. The other three runtimes (1070560 scout, 1391110 soldier, 1628350 sniper) have never shown this problem — only 4183110.

I was able to force a real, complete install of the runtime using steamcmd directly, but only with an authenticated account login — anonymous login fails outright with ERROR! Failed to install app '4183110' (No subscription). With an authenticated account it succeeds (Success! App '4183110' fully installed.) and produces a correct .acf (real SizeOnDisk, BytesDownloaded matching BytesToDownload, InstalledDepots populated with depot 4183111). Proton-GE Latest and Proton Experimental then work correctly — DXVK/Vulkan device init succeeds, games reach their main menu — for the remainder of that session.

However, at some point after that — not necessarily a reboot, possibly just normal Steam client activity — the .acf reverts back to the zeroed-out state, even though the ~650 MB of actual runtime files remain untouched on disk (confirmed with du -sh, consistently ~600-650 MB before and after the manifest resets). This is not a failed or corrupted download: the download completes correctly, and then the client's own record of it is subsequently invalidated by something. Running "Verify integrity of tool files" from the Library UI reports "All files successfully validated" while simultaneously showing "Size of installation: 0 B" — it's validating against a manifest that expects zero installed depots, so it never detects or repairs the mismatch between the real files on disk and the registered (empty) state.

Re-running steamcmd with authenticated login fixes it again temporarily (one retry was needed the second time, after a transient ERROR! Failed to install app '4183110' (Invalid platform) on the first attempt — an immediate identical re-run succeeded). But even with a freshly confirmed-good .acf and Steam closed during the entire steamcmd run (to rule out the client interfering mid-install), launching a game through the normal Steam Play button still failed on the next attempt, this time with no "Failed to load manifest" line in compat_log.txt at all — the tool's command prefix was set successfully — suggesting the failure point may shift around, or that the manifest state checked at launch time can differ from what was on disk moments earlier.

This looks closely related to #13199, #13248, and GloriousEggroll/proton-ge-custom#534, but I don't think any of those threads describe the specific "install completes correctly via steamcmd, then silently reverts to a zeroed-out ghost state on its own" behavior, which is why I'm filing this separately.

Additional observations:

• Anonymous steamcmd login failing with No subscription for AppID 4183110, while other Steam Linux Runtime tools install fine anonymously, suggests this specific app's ownersonly licensing may be resolving differently than the others — possibly related to why the graphical client (which should already be authenticated) fails to resolve/maintain the same entitlement correctly.
• SteamDB shows no build update for AppID 4183110 since early June, so this isn't caused by a recent change to the runtime package itself — it points back to Steam client-side behavior.

Steps for reproducing this issue:

1. On a system where Steam Linux Runtime 4.0 (AppID 4183110) is not yet installed, select Proton Experimental, Proton 11.0, or Proton-GE Latest as the compatibility tool for any game/shortcut and try to launch it.
2. Observe the launch fail (silently, or with "Compatibility tool failed"), and check ~/.steam/steam/logs/compat_log.txt for Failed to load manifest for tool 4183110! / unsupported version 0.
3. Check Library → Tools: Steam Linux Runtime 4.0 shows as installed (no Install button available) despite the game failing.
4. Check ~/.steam/steam/steamapps/appmanifest_4183110.acf: SizeOnDisk and BytesDownloaded are 0, InstalledDepots is empty.
5. Check ~/.steam/steam/steamapps/common/SteamLinuxRuntime_4/: folder exists, subfolders are present but empty (0 bytes), no toolmanifest.vdf.
6. Close Steam. Run steamcmd +@sSteamCmdForcePlatformType linux +login <your account> +app_update 4183110 validate +quit (anonymous login will fail with No subscription).
7. Confirm the .acf now shows correct SizeOnDisk/BytesDownloaded/InstalledDepots, and that the affected Proton builds now launch games correctly.
8. Continue using Steam normally for a while (exact trigger not isolated — happened across a mix of closing/reopening the client and a full reboot). Re-check the .acf and/or try launching an affected game again.
9. Observe the failure returns, and the .acf has reverted to the zeroed-out state from step 4, despite the runtime files from step 6 still being present on disk.