The enforce service runs as root (no User=) but sets DISPLAY=:0, so any GUI
it starts lands on the desktop session. Two resolvers disagreed about who to
drop privileges to:
library_hider._resolve_desktop_user() read STEAM_ENFORCER_DESKTOP_USER
game_install._get_real_user() read only SUDO_USER or USER
systemd sets neither of the latter, so _get_real_user() returned None under
the service and every `geteuid() == 0 and real_user and ...` guard fell
through to running as root. Steam answered with a zenity modal ("Cannot run
as root user", /usr/lib/steam/steam:261) on screen.
Confirmed from the live process tree: root `bash /usr/lib/steam/steam
-cef-disable-gpu ... steam://install/618510` with a root zenity child. It
never reached the journal, because that text goes to zenity and _run_as_user
sends child output to DEVNULL.
- _desktop_env: add resolve_desktop_user/desktop_uid/desktop_user_cmd. Only
the argv builder is shared, never the spawn call: tests/_no_subprocess.py
patches subprocess per module by name, so a spawn site in an unpatched
module could fire a real `sudo -u kuhy steam`.
- game_install._get_real_user: delegate to the shared resolver. This alone
also fixes the root `steam -silent` in _ensure_steam_running and the
no-op os.chown on new appmanifests.
- _trigger_steam_install / enforcer.send_notification: drop privileges.
send_notification had no DBUS_SESSION_BUS_ADDRESS, so it silently reached
nobody for all six of its callers.
- _run_as_user: fail closed. Running unchanged as root when no desktop user
resolves is what put the modal on screen; refuse and log instead.
Also stop the retry storm behind it. steamapps does not exist (Steam has
never completed sign-in), so is_game_installed() was always False and the
loop re-triggered every allowed game every pass: 1656 attempts in 30
minutes, service RSS 1.5 GB (peak 4.3 GB), a FileNotFoundError traceback
each time. Guard install_game and _reinstall_missing_allowed on
steam_library_ready() -- a missing library means no install can succeed by
any route, so this is a correctness check rather than a tuned retry limit.
The module splits here are forced by the pre-commit 250-line gate, which
blocks any commit touching an over-cap file: game_install, library_hider and
_enforce_loop were already over before this change. They are split by
responsibility (_cdp transport, _steam_launch lifecycle, _steam_process
spawning, _steam_errors, _steam_client, _game_names, game_uninstall,
_enforce_steps, _owned_apps_cache, _echo, _protected_apps). game_install and
library_hider re-export their old public names, so the 15 modules that
import from them are untouched by this commit.
Verified as real root under the unit's environment: argv is now
`sudo -u kuhy env DISPLAY=:0 ... xdg-open steam://install/...` for both the
installer and notify-send; three enforce passes spawn no process and log
once; _run_as_user refuses with no desktop user. After restart: 0 retries,
0 tracebacks, 0 root-owned files under ~/.local/share/Steam, RSS 342 MB.
1311 tests pass. _desktop_env and _steam_state at 100% branch coverage.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016A1EYiv7e7HGhET84oa9M3
