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feat(vdisplay): harden keep-alive reconnect — same-client preempt, quit-skips-linger, configurable idle

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On-glass testing (Test 2, KWin .116) surfaced that a reconnect within the QUIC idle-timeout
window (~8s) lands on a fresh SECOND display instead of reusing the kept one: the old session
was still Active (not yet Lingering), so the registry's keep-alive reuse (which only matches
Lingering) skipped it and the old session kept streaming to nobody. Three fixes:

#3 Same-client reconnect preempt (the real fix): admission::preempt_same_identity() lists a
   reconnecting client's OWN still-live session(s) (same cert fingerprint); serve_session signals
   their stop + waits the release grace BEFORE acquiring, so the zombie tears down → its display
   lingers → the reconnect REUSES it instead of making a second. Implements the "preempts
   downstream" the admission docs already promised. Independent of the mode_conflict policy; the
   pure core (same_identity_stops) is unit-tested.

#2 Deliberate quit skips linger: a client that deliberately disconnects closes the QUIC connection
   with QUIT_CLOSE_CODE (0x51, shared in core::quic); the host reads the ApplicationClosed reason
   and tears the display down immediately (registry release() gained force_immediate →
   Linger::Immediate; multi-session-safe via the pure lifecycle machine), while a bare disconnect
   still lingers for reconnect. Threaded via a session quit flag → the DisplayLease.
   NativeClient::disconnect_quit() + punktfunk-probe --quit drive it; GameStream (Quit App /
   h_cancel) is a documented follow-up.

#1 Configurable disconnect-detection latency: the QUIC control-connection idle timeout
   (stream_transport, 8s default) is host-tunable via --idle-timeout-ms / PUNKTFUNK_IDLE_TIMEOUT_MS,
   clamped >=1s with a keep-alive that scales to it so a live session never false-closes. Default
   unchanged (8s stays load-bearing for the Windows IDD-push reconnect flow).

Workspace check + 63 core / 215 host / 47 vdisplay tests green; clippy clean.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
This commit is contained in:
Enrico Bühler
2026-07-05 16:41:06 +00:00
parent c1acfe8b85
commit b53710da1a
9 changed files with 272 additions and 38 deletions
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include/punktfunk_core.h
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@@ -274,6 +274,15 @@
#define VIDEO_CAP_HOST_TIMING 8
#endif
#if defined(PUNKTFUNK_FEATURE_QUIC)
// QUIC application error code a punktfunk/1 client closes the control connection with on a
// **deliberate quit** (a user "stop", not a network drop). The host reads it off the connection's
// `ApplicationClosed` reason and tears the session's virtual display down immediately, skipping the
// keep-alive linger; any other close reason (idle timeout, reset, a bare code 0) still lingers so a
// reconnect can resume. Shared so host + every client agree on the code.
#define QUIT_CLOSE_CODE 81
#endif
#if defined(PUNKTFUNK_FEATURE_QUIC)
// [`Hello::video_codecs`] bit: the client can decode H.264 / AVC. The GPU-less **software**
// encode path (openh264) emits H.264, so a client that wants to stream from a software host MUST