Field report (Nobara 43 HTPC): switching the host to Steam Game Mode
mid-stream permanently black-screened the box. Live-proven root cause on
a Nobara repro VM: our takeover masks the box's gamescope-session-plus
unit, plasmalogin's Relogin=true then fails its session Exec repeatedly
and trips systemd's start limit within ~1 s — the display manager dies,
and our restore verb (unmask + user start) cannot bring a seatless
gamescope back. Only 'reset-failed + restart' of the DM recovers.
The takeover is now display-manager-flavor-aware:
- SDDM (Bazzite/SteamOS) keeps the proven mask+SIGKILL path unchanged.
- plasmalogin/unknown DMs never mask: with privilege (root or an
operator polkit rule scoped to the DM unit — documented) the host
stops the DM for the stream and restores it with reset-failed +
restart (PUNKTFUNK_RECOVER_SESSION_CMD as fallback), recorded in the
persisted takeover state so a host crash still restores; without
privilege the managed takeover degrades to ATTACH and mirrors the
box's live Game Mode instead of destabilizing the seat. Both legs of
the privileged cycle live-verified on the repro VM (headless managed
session works with zero login sessions; render nodes are 0666).
A loaded-but-inactive leftover instance never triggers the DM stop.
Companion fixes from the same triage:
- ensure_box_gamescope_mode gains the attach-only rebuild-probe guard
both managed paths already had (stale post-capture-loss detection
restarted the box's unit), and no longer re-modes a box that drives a
physical display — attach mirrors on-glass; re-mode is the
headless-box model.
- Capture-loss rebuilds targeting gamescope get a 100 s budget: the
40 s budget expired inside the first 45 s Steam-cold-start launch
attempt, a guaranteed single-shot failure.
- A PUNKTFUNK_COMPOSITOR pin now WARNs once per capture loss when the
live session no longer matches it (the pin disables
session-following — the reporter's original stream-death trigger).
- A managed session that took nothing over (client gamescope pin beside
a live desktop) is stopped on disconnect instead of being orphaned
forever.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
enricobuehlerandClaude Fable 5
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