The secure (Winlogon: UAC/lock/login) desktop presents via fullscreen
independent-flip/MPO — it scans out bypassing DWM composition, so DXGI Desktop
Duplication returns born-lost DXGI_ERROR_ACCESS_LOST (the client sees black; the
UAC only "flashes" during the brief composed transition). Confirmed live: stable
4090 LUID across the storm (NOT reparenting) on an FP16 HDR output, recovering
only when the screen changes.
Fix (non-input, no system-wide registry change): capture/composed_flip.rs keeps a
tiny click-through near-invisible TOPMOST LAYERED window alive on the current
input desktop. Any visible window on the output disqualifies independent-flip →
DWM composites → DDA can capture. A dedicated thread follows the input desktop
(Default↔Winlogon) and recreates the window there on each switch (a window is
bound to its desktop), re-asserting topmost + pumping messages every 200ms.
Started for the two-process stream's lifetime; gated by PUNKTFUNK_FORCE_COMPOSED
(default on, =0 to disable). Needs GENERIC_ALL on OpenInputDesktop for
DESKTOP_CREATEWINDOW (0x80070005 otherwise). Validated: overlay creates on the
Default desktop; live lock test pending.
Also includes SET_RENDER_ADAPTER (sudovda.rs, Apollo item #16): pins the IDD
render GPU to the NVENC GPU before ADD — issued + accepted live, though the
secure-desktop storm was proven to be independent-flip (stable LUID), not
reparenting, so it's correctness/hygiene here rather than this bug's fix.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
enricobuehler
ef4786387e