[Feature Request] Add a step to clear Pacman's pkg cache in /var when using steamos-unminimize

[matte-schwartz]

Your system information

• Steam client version: 1726256783
• SteamOS version: 3.6.13
• Opted into Steam client beta?: Yes
• Opted into SteamOS beta?: Yes
• Have you checked for updates in Settings > System?: No

Please describe your issue in as much detail as possible:

When switching between SteamOS branches (i.e. Main and Preview), I've noticed that many packages in my Pacman cache will report as corrupted after switching, and the fix I've found is that I need to manually clear out my package cache in /var. Maybe adding an optional step to clear out the cache on request, or triggering the same when branches change, could be useful here?

Steps for reproducing this issue:

1. Start on SteamOS Preview, and use steamos-devmode enable and steamos-unminimize --dev
2. Switch branches, update, and attempt to follow the same steps
3. Now when running steamos-unminimize --dev again, you should start to see corrupted package errors after it checks package integrity.

Logs:

(863/863) checking package integrity                                                                                                                                                                             [####################################################################################################################################] 100%
error: glib2: signature from "GitLab CI Package Builder <[email protected]>" is invalid
:: File /var/cache/pacman/pkg/glib2-2.78.6-1.1-x86_64.pkg.tar.zst is corrupted (invalid or corrupted package (PGP signature)).
Do you want to delete it? [Y/n] n
error: wayland: signature from "GitLab CI Package Builder <[email protected]>" is invalid
:: File /var/cache/pacman/pkg/wayland-1.23.0-1-x86_64.pkg.tar.zst is corrupted (invalid or corrupted package (PGP signature)).
Do you want to delete it? [Y/n] n
error: libarchive: signature from "GitLab CI Package Builder <[email protected]>" is invalid
:: File /var/cache/pacman/pkg/libarchive-3.7.2-1.1-x86_64.pkg.tar.zst is corrupted (invalid or corrupted package (PGP signature)).
Do you want to delete it? [Y/n] n
error: ddcutil: signature from "GitLab CI Package Builder <[email protected]>" is invalid
:: File /var/cache/pacman/pkg/ddcutil-2.1.4-1.1-x86_64.pkg.tar.zst is corrupted (invalid or corrupted package (PGP signature)).
Do you want to delete it? [Y/n] n
error: kwin: signature from "GitLab CI Package Builder <[email protected]>" is invalid
:: File /var/cache/pacman/pkg/kwin-5.27.10-3-x86_64.pkg.tar.zst is corrupted (invalid or corrupted package (PGP signature)).
Do you want to delete it? [Y/n] n
error: less: signature from "GitLab CI Package Builder <[email protected]>" is invalid
:: File /var/cache/pacman/pkg/less-1:643-1.1-x86_64.pkg.tar.zst is corrupted (invalid or corrupted package (PGP signature)).
Do you want to delete it? [Y/n] n
error: openssh: signature from "GitLab CI Package Builder <[email protected]>" is invalid
:: File /var/cache/pacman/pkg/openssh-9.6p1-3.1-x86_64.pkg.tar.zst is corrupted (invalid or corrupted package (PGP signature)).
Do you want to delete it? [Y/n] n
error: plasma-remotecontrollers: signature from "GitLab CI Package Builder <[email protected]>" is invalid
:: File /var/cache/pacman/pkg/plasma-remotecontrollers-5.27.11-1.2-x86_64.pkg.tar.zst is corrupted (invalid or corrupted package (PGP signature)).
Do you want to delete it? [Y/n] n
error: pyzy: signature from "GitLab CI Package Builder <[email protected]>" is invalid
:: File /var/cache/pacman/pkg/pyzy-1.1-2.2-x86_64.pkg.tar.zst is corrupted (invalid or corrupted package (PGP signature)).
Do you want to delete it? [Y/n] n
error: zenity-gtk3: signature from "GitLab CI Package Builder <[email protected]>" is invalid
:: File /var/cache/pacman/pkg/zenity-gtk3-3.44.2-2-x86_64.pkg.tar.zst is corrupted (invalid or corrupted package (PGP signature)).
Do you want to delete it? [Y/n] n
error: steam-jupiter-stable: signature from "GitLab CI Package Builder <[email protected]>" is invalid
:: File /var/cache/pacman/pkg/steam-jupiter-stable-1.0.0.79-1.1-x86_64.pkg.tar.zst is corrupted (invalid or corrupted package (PGP signature)).
Do you want to delete it? [Y/n] n
error: failed to commit transaction (invalid or corrupted package)
Errors occurred, no packages were upgraded.