Hardens the virtual-display → capture → encode bring-up against the transient
failures that surfaced as black screens / wrong refresh on cold KDE sessions.
- m3: build_pipeline_with_retry wraps the initial vd.create() + first-frame with
bounded exponential backoff (4 attempts, 500ms→2s). is_permanent_build_error
classifies config/version/missing-tool failures so they fail fast instead of
burning the retry budget. Encoder + frame clock now pace to the *achieved*
refresh reported in VirtualOutput::preferred_mode, not the requested rate.
- capture/linux: PortalCapturer::Drop sends a pipewire channel quit and joins the
thread, so a dropped/failed/retried capturer releases its PipeWire thread + EGL/
CUDA context promptly instead of leaking it to process exit. First-frame timeout
now reports the node id and distinguishes "format never negotiated" from
"negotiated but no buffers arrived" via a negotiated flag set in param_changed.
- vdisplay/kwin: set_custom_refresh reads back the active mode from kscreen-doctor
and returns the refresh KWin actually gave us (a rejected custom mode silently
leaves the output at 60Hz); create() carries it into preferred_mode.
- vdisplay/gamescope: find_gamescope_node requires the Video/Source object (the
node.name=gamescope tag is on two objects; the other wedges the link); a version
check warns on <3.16.22 (the PipeWire-1.6 capture-deadlock signature).
Live-validated against headless KWin: 720p120 build with requested=120 achieved=120,
zero-copy CUDA frames, and no per-session thread accumulation across back-to-back
sessions. Tests: +3 unit (retry classifier, gamescope version parse); 49 host tests
green, clippy/fmt clean.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
enricobuehler
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