The secure-desktop DDA leg went black with HDR on: legacy DuplicateOutput (the SDR-era
API) can't capture an FP16/HDR desktop, and dropping the SudoVDA out of HDR is denied on
the Winlogon desktop (so the SDR-drop attempt just churned and stayed black).
Instead capture HDR natively on the DDA path — the capturer already has the full
FP16→BT.2020 PQ→R10G10B10A2 conversion (hdr_fp16 path), it just never requested FP16.
Thread a want_hdr flag into duplicate_output: for an HDR session request
DuplicateOutput1 with FP16 first and retry it (5×) instead of bailing to the
HDR-incapable legacy fallback. The secure-desktop mux now reads the monitor's real HDR
state and opens DDA in HDR when set — no advanced-color toggling at all. The
normal-desktop DDA overlay/flip issues that pushed us to WGC don't apply to the composed
Winlogon UI. want_hdr is threaded through every (re)duplication incl. ACCESS_LOST recovery.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
enricobuehler
b0c518c21b