# Session-aware host — known limitations & follow-ups

> **Status:** Session detection SHIPPED — host auto-detects the live session (Gaming / KDE / GNOME /
> wlroots) **per connect** and routes video+input at it; opt-in mid-stream switch watcher
> (`PUNKTFUNK_SESSION_WATCH=1`). Code: `crates/punktfunk-host/src/vdisplay.rs` +
> `vdisplay/linux/{gamescope,kwin,mutter}.rs`. Items #2 + #3 resolved in code (`3363576`); this doc is
> trimmed to the still-open limitations + their design rationale.

The host auto-detects the live session per connect and routes both video and input at it — managed
gamescope at the client's resolution in Steam Gaming Mode, a KWin/Mutter virtual output at the
client's resolution on a Desktop. A watcher (opt-in: `PUNKTFUNK_SESSION_WATCH=1`) follows a
Gaming↔Desktop switch **mid-stream** and rebuilds the backend in place without a reconnect.

Live-validated on the Bazzite F44 box (`bazzite-deck-nvidia:testing`, RTX 4090): Desktop KDE at
5120×1440 + input; Gaming managed at 5120×1440; warm-session reuse on quick reconnect; Feature B
video-switch both directions.

(Resolved: **#2 mid-stream-switch input** — `vdisplay::settle_desktop_portal()`; **#3 KWin/Mutter
virtual output primary** — `apply_session_env` defaults `PUNKTFUNK_KWIN_VIRTUAL_PRIMARY` /
`PUNKTFUNK_MUTTER_VIRTUAL_PRIMARY` on for the auto desktop path. Both shipped in `3363576`; details in
git history.)

> **Update 2026-07-05:** items **#1** (SIGKILL teardown / keep-warm) and **#7** (restore-guard /
> keep-warm interaction) are picked up by `design/gamemode-and-dedicated-sessions.md` **Part A3**
> — the managed session's restore becomes registry-owned and policy-driven (`keep_alive` replaces
> the hardcoded 5 s debounce; "keep warm" = `keep_alive: forever`), with the SIGKILL-teardown
> experiment folded into that stage's validation. That doc also covers the display-management
> registry's game-mode conflicts (ownership classes, stale-node reuse) and dedicated per-launch
> gamescope game sessions.

## Still parked

### 1. F44 gamescope teardown corrupts the GPU context
Every gamescope teardown on this box (stop the autologin on connect; stop the managed session on
restore) risks leaking the NVIDIA GPU context — surfaces as `CUDA_ERROR_ILLEGAL_STATE` (401) in
`cuCtxCreate` / `vkCreateDevice` `VK_ERROR_INITIALIZATION_FAILED` (-3), then a black screen that
**needs a reboot**. The 5 s debounced restore + the desktop restore-guard cut the teardown *count*
but don't eliminate it. Options, in order of preference:
- **SIGKILL the gamescope on teardown** instead of `systemctl stop` (SIGTERM). Hypothesis: skipping
  gamescope's buggy SIGTERM teardown handler (the part that SIGSEGVs, exit 139) lets the process die
  hard and the driver reclaim its GPU resources cleanly via normal process exit — no half-torn-down
  context. Change `stop_autologin_sessions` + `stop_session` (`vdisplay/linux/gamescope.rs`, both
  still use `systemctl --user stop` = SIGTERM) to `systemctl --user kill --signal=SIGKILL <unit>`
  (+ a follow-up `stop`/`reset-failed` to clear unit state). **Untested** — this is the first thing
  to try; it would preserve "managed client-res gaming AND TV-shows-gaming-when-idle".
- **Keep the managed session warm** (no per-disconnect restore): spawn once, reuse forever, never
  tear down → ~1 teardown per host lifetime. Tradeoff: the TV is blank/idle when no client is
  connected (the autologin is never restored; return to gaming manually).
- Upstream gamescope/driver fix.

## Lower priority / polish

### 4. Mid-stream-switch input loss window (~6 s)
During the libei portal setup on a switch, buffered input drops (`libei: DROP — no resumed device`,
hundreds of events). Polish: pre-warm the portal, or hold events instead of dropping during the
device-resume window.

### 5. NVENC `InitializeEncoder failed: invalid param` (recovered)
At 5120×1440@240 the first NVENC open fails with `invalid param (8)` and **recovers** via the 2-way
split-encode path (the stream is live). Cosmetic but noisy — investigate the first-attempt failure /
silence the log.

### 6. NVENC HEVC bitrate cap (~800 Mbps on the RTX 4090)
HEVC opens at the GPU's max (~800 Mbps) when a higher rate is requested (e.g. 1600). Not a bug;
consider preferring AV1 when the client requests >~800 Mbps HEVC, and surface the cap in the
speed-test / bitrate UI.

### 7. Restore-guard / keep-warm model interaction
`do_restore_tv_session`, when a desktop is active, still stops the idle managed gamescope (a teardown
— leak risk per #1) and consumes `STOPPED_AUTOLOGIN` (so a later return-to-gaming won't auto-restore
the TV session). Resolve together with the keep-warm decision in #1.

### 8. Feature B is opt-in
The mid-stream watcher is gated behind `PUNKTFUNK_SESSION_WATCH=1` pending broader validation. Promote
to default-on once #2 (mid-stream input) lands and it's exercised on more boxes.

## Open items

1. **F44 gamescope teardown corrupts the GPU context** (#1) — try SIGKILL on teardown
   (`stop_autologin_sessions` / `stop_session` in `vdisplay/linux/gamescope.rs`), else keep the
   managed session warm, else upstream fix.
2. **Mid-stream-switch input-loss window (~6 s)** (#4) — pre-warm the portal or buffer/hold events
   instead of dropping during the device-resume window.
3. **NVENC `InitializeEncoder failed: invalid param` noise at 5120×1440@240** (#5) — recovers via
   split-encode; investigate the first-attempt failure / silence the log.
4. **NVENC HEVC ~800 Mbps cap on the RTX 4090** (#6) — consider preferring AV1 above it + surface the
   cap in the speed-test / bitrate UI.
5. **Restore-guard / keep-warm interaction** (#7) — couples to #1; resolve together.
6. **Feature B (`PUNKTFUNK_SESSION_WATCH`) still opt-in** (#8) — promote to default-on after #2 lands
   and it's exercised on more boxes.
