Bug Report: steampipe_fixups.py restore empties default_pfx but wineboot is never called to rebuild it

System Information

• OS: Ubuntu 24.04.4 LTS (Noble Numbat)
• Kernel: 6.17.0-20-generic (HWE)
• GPU: NVIDIA GeForce GTX 1080 Ti
• Driver: nvidia-driver-570 (570.211.01)
• Steam client: 1773426488
• Proton versions affected: Proton Experimental, Proton 9.0 (Beta), Proton Hotfix, GE-Proton10-32

Description

At every game launch, steampipe_fixups.py restore is called and empties files/share/default_pfx/ — removing all DLL files from drive_c/windows/system32/ and drive_c/windows/syswow64/, as well as fonts, registry files, and other prefix contents.

After this cleanup, make_default_prefix() in the proton script is never called to rebuild default_pfx because missing_default_prefix() only checks whether the directory exists, not whether it contains valid content:

def missing_default_prefix(self):
    return not os.path.isdir(self.default_pfx_dir)

def make_default_prefix(self):
    with self.dist_lock:
        local_env = dict(g_session.env)
        if self.missing_default_prefix():
            local_env["WINEPREFIX"] = self.default_pfx_dir
            local_env["WINEDEBUG"] = "-all"
            g_session.run_proc([self.wine_bin, "wineboot"], local_env)
            g_session.run_proc([self.wineserver_bin, "-w"], local_env)

Since steampipe_fixups.py restore empties the directory without removing it, missing_default_prefix() returns False and wineboot is never invoked. The result is that default_pfx remains empty, and every subsequent game launch fails with:

FileNotFoundError: [Errno 2] No such file or directory:
'.../files/share/default_pfx/drive_c/windows/system32/d3d8.dll'

Steps to Reproduce

1. Install any Proton version on Ubuntu 24.04 with kernel 6.17
2. Launch any Windows game using Proton
3. Observe that steampipe_fixups.py restore empties default_pfx
4. Observe that wineboot is never called to rebuild it
5. All subsequent game launches fail silently

Expected Behavior

After steampipe_fixups.py restore runs, make_default_prefix() should detect that default_pfx is empty or invalid and call wineboot to rebuild it.

Suggested Fix

missing_default_prefix() should check for the presence of expected content, not just directory existence. For example:

def missing_default_prefix(self):
    system32 = os.path.join(self.default_pfx_dir, "drive_c/windows/system32")
    if not os.path.isdir(system32):
        return True
    dll_count = len([f for f in os.listdir(system32) if f.endswith(".dll")])
    return dll_count < 100

Workaround

Manually delete the entire default_pfx directory before launching a game, forcing missing_default_prefix() to return True and triggering a rebuild via wineboot.

Log Evidence

inotifywait — default_pfx deletions with no subsequent CREATE events

2026-04-11 19:42:27 .../files/share/default_pfx/drive_c/windows/syswow64/ win32s16.dll DELETE
2026-04-11 19:42:27 .../files/share/default_pfx/drive_c/windows/syswow64/ typelib.dll DELETE
2026-04-11 19:42:27 .../files/share/default_pfx/drive_c/windows/syswow64/ libvkd3d-shader-1.dll DELETE
2026-04-11 19:42:27 .../files/share/default_pfx/drive_c/windows/syswow64/ libvkd3d-1.dll DELETE
2026-04-11 19:42:27 .../files/share/default_pfx/drive_c/users/steamuser/ AppData DELETE,ISDIR
2026-04-11 19:42:27 .../files/share/default_pfx/drive_c/users/ steamuser DELETE,ISDIR
2026-04-11 19:42:27 .../files/share/default_pfx/ system.reg DELETE
2026-04-11 19:42:27 .../files/share/default_pfx/ .update-timestamp DELETE
2026-04-11 19:42:27 .../files/share/default_pfx/ dosdevices DELETE,ISDIR
# [490 lines total — all DELETE, zero CREATE events]

Proton log (steam-[gameid].log) — FileNotFoundError after cleanup

======================
Proton: 1775583929 experimental-10.0-20260407
SteamGameId: [gameid]
Command: ['[game executable]', '/Steam', '/novr']
Options: {'forcelgadd'}
depot: 3.0.20260218.209091
pressure-vessel: 0.20260218.0
Kernel: Linux 6.17.0-20-generic x86_64
======================
Traceback (most recent call last):
  File ".../proton", line 2100, in <module>
    g_session.init_session(sys.argv[1] != "runinprefix")
  File ".../proton", line 1979, in init_session
    g_compatdata.setup_prefix()
  File ".../proton", line 1128, in setup_prefix
    try_copy(g_proton.default_pfx_dir + "drive_c/windows/system32/" + f + ".dll", ...)
  File ".../proton", line 169, in try_copy
    copyfile(src, dst)
  File ".../proton", line 231, in copyfile_reflink
    with open(srcname, 'rb', buffering=0) as src:
FileNotFoundError: [Errno 2] No such file or directory:
  '.../files/share/default_pfx/drive_c/windows/system32/d3d8.dll'

journalctl — confirming the error in system log

Apr 11 19:33:03 [hostname] steam[PID]: FileNotFoundError: [Errno 2] No such file or directory:
  '.../Proton - Experimental [appid]/files/share/default_pfx/drive_c/windows/system32/d3d8.dll'
Apr 11 19:33:03 [hostname] steam[PID]: Game Recording - game stopped [gameid=[gameid]]
Apr 11 19:33:03 [hostname] steam[PID]: Removing process [PID] for gameID [gameid]

Additional Notes

This issue affects all installed Proton versions simultaneously, suggesting it is triggered by a common code path in steampipe_fixups.py. The issue has persisted across multiple kernel and Proton updates over approximately 6-8 months.

inotifywait confirmed that all 490 deletions occur within the same second (batch delete), and no CREATE events follow — confirming that wineboot is never invoked after the cleanup.