Your system information

• Steam client version (build number or date): 1769025840
• Distribution (e.g. Ubuntu): Debian 13
• Opted into Steam client beta?: No
• Have you checked for system updates?: Yes
• Steam Logs: steam-logs.tar.gz
• Steam Runtime Diagnostics
• GPU: Nvidia

Please describe your issue in as much detail as possible:

I attempted to install Sonic Frontiers to my gaming partition at ~/Games, and it didn't show up as installed, or with any errors. Afterwards, I couldn't install or update anything else on Steam, and instead got a 'disk write error,' and my content log was being spammed with Failed to write app state file as in #12150 (and possibly #12559).

Removing ~/Games as a library folder didn't work; clicking the remove button did nothing. After unmounting that partition, I could remove the library folder in Steam. When I tried to re-add it, nothing happened, as some people describe in #9640. Instead of a permissions error, though, console_linux.txt showed a not found error for the test script:

[2026-01-29 21:08:38] Couldn't write /.steam_exec_test.sh: Permission denied
[2026-01-29 21:08:38] Couldn't write /boot/efi/.steam_exec_test.sh: Permission denied
[2026-01-29 21:08:38] sh: 1: /home/autumn/Games/.steam_exec_test.sh: not found
[2026-01-29 21:08:38] Failed system("/home/autumn/Games/.steam_exec_test.sh") in execute test: 32512

I saw a new ~/games folder was created, with a lowercase g instead of uppercase. It contained an all-uppercase version of the SteamLibrary folder from ~/Games, with a few folders from Sonic Frontiers, a couple config files from No Man's Sky, and its own libraryfolder.vdf, but no other games that are on that drive.

~/games~ took 7s 
❯ tree
.
└── STEAMLIBRARY
    ├── libraryfolder.vdf
    └── STEAMAPPS
        └── COMMON
            ├── NO MAN'S SKY
            │   ├── BINARIES
            │   │   └── SETTINGS
            │   │       ├── GCMODSETTINGS.MXML
            │   │       ├── GCUSERSETTINGSDATA.MXML
            │   │       ├── TKGAMESETTINGS.MXML
            │   │       └── TKGRAPHICSSETTINGS.MXML
            │   └── GAMEDATA
            │       └── SHADERCACHE
            └── SonicFrontiers
                └── image
                    └── x64
                        └── raw
                            ├── bmpfont
                            ├── boss
                            ├── character
                            ├── decotext
                            │   ├── editor
                            │   └── parameter2
                            ├── dlc
                            │   ├── dlccrm
                            │   ├── dlcddx
                            │   ├── dlcmhr
                            │   └── dlcxmas
                            ├── enemy
                            ├── event
                            │   └── scene
                            ├── gedit
                            ├── general
                            │   └── resident_general
                            ├── hedgehog
                            │   ├── font
                            │   ├── level
                            │   └── sound
                            │       └── debug
                            ├── LICENSE
                            ├── miniboss
                            ├── minigame
                            ├── misc
                            └── movie

40 directories, 5 files

After trashing that folder, Steam could immediately re-add the library folder and detect its games without issue. I assume this is a case sensitivity bug somewhere, but writing this, I'm concerned I might just be going crazy. ¯\(ツ)/¯

] library_folder_add "/home/autumn/Games"
Failed mounting that path!
 
] library_folder_add "/home/autumn/Games"
Mounted path "/home/autumn/Games" : index 2
CAPIJobRequestUserStats - Server response failed 2
CAPIJobRequestUserStats - Server response failed 2
CAPIJobRequestUserStats - Server response failed 2
CAPIJobRequestUserStats - Server response failed 2
 
] library_folder_add "/home/autumn/Games/SteamLibrary"
Mounted path "/home/autumn/Games/SteamLibrary" : index 2

Steps for reproducing this issue:

1. Install Steam
2. Mount a second partition/drive to a path with mixed case (e.g. ~/Games, not ~/games). Ensure your own user has read/write/execute privileges to that path.
3. Add the second partition/drive to the Steam client.
4. Install Skyrim SE, and see that it works (or whatever other game; I have many installed).
5. Install Sonic Frontiers. It downloads all the way, but disappears after downloading.
6. Attempt to install Sonic Frontiers again. It downloads shadercache, then immediately gives a Disk Error.
7. Attempt to install any other pending updates. In my case, every download gave an immediate disk error.