fix(host/windows): honor the SudoVDA's real HDR state (stop wiping the user's HDR toggle)

HDR streamed nothing and "didn't persist" because build() forced the SudoVDA's
advanced-color state to match the handshake bit_depth on every build — with an
8-bit-negotiated session (the common case: clients advertise no 10-bit cap) that
meant set_advanced_color(false) on every connect, wiping a user's deliberate
Windows HDR toggle on the virtual display.

But the whole pipeline already follows the monitor's REAL HDR state: WGC captures
FP16 when HDR is on, NVENC forces Main10 + BT.2020 PQ from the 10-bit capture
format regardless of the negotiated depth (encode/nvenc.rs), and the client
auto-detects PQ from the HEVC VUI. So the negotiated bit_depth must NOT drive the
monitor's colorspace.

- build(): only ever ENABLE HDR (proactively, for a negotiated 10-bit session);
  never force it off. A user-enabled HDR session now persists and flows end-to-end.
- secure-desktop mux: gate the HDR→SDR drop (for the DDA leg) on the monitor's
  ACTUAL advanced-color state at switch time, not bit_depth — so an HDR session
  with an 8-bit handshake still drops correctly for Winlogon and restores after.
- sudovda: add advanced_color_enabled() reader (DISPLAYCONFIG_GET_ADVANCED_COLOR_INFO).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

crates/punktfunk-host/src/m3.rs

@@ -2344,20 +2344,24 @@ fn virtual_stream_relay(
         let target = vout.win_capture.clone().ok_or_else(|| {
             anyhow!("SudoVDA target not yet an active display (needs a WDDM GPU to activate it)")
         })?;
-        // Force the SudoVDA's advanced-color (HDR) state to MATCH the session bit depth BEFORE the WGC
+        // HDR is driven by the SudoVDA monitor's ACTUAL advanced-color state, not the handshake bit
-        // helper captures it. The advanced-color state PERSISTS on the monitor across sessions, so an
+        // depth: the whole pipeline follows the monitor (WGC captures FP16 when HDR is on; NVENC forces
-        // 8-bit (SDR) session could otherwise inherit HDR left on by a prior 10-bit run (or our own
+        // Main10 + BT.2020 PQ from the 10-bit capture format regardless of the negotiated depth; the
-        // earlier toggle) → the helper captures HDR FP16 while the encoder is 8-bit SDR → broken image.
+        // client auto-detects PQ from the HEVC VUI). So:
-        // Runs on every build (initial + mode-switch + return-from-secure rebuild), keeping WGC's format
+        //   - a negotiated 10-bit session PROACTIVELY enables HDR on the monitor (below), but
-        // consistent with the encoder. (HDR independent-flip on the secure desktop is handled separately
+        //   - we must NEVER force HDR *off* here — that would wipe out a user's deliberate Windows HDR
-        // by dropping to SDR for the DDA leg.)
+        //     toggle on the virtual display on every build (the "HDR doesn't persist" bug). Leaving the
+        //     monitor's state alone lets a user-enabled HDR session flow through end-to-end.
+        // The secure-desktop HDR drop (for the DDA leg) keys off the monitor's real state in the mux loop.
         #[cfg(target_os = "windows")]
+        if bit_depth >= 10 {
             unsafe {
-            if crate::vdisplay::sudovda::set_advanced_color(target.target_id, bit_depth >= 10) {
+                if crate::vdisplay::sudovda::set_advanced_color(target.target_id, true) {
                     // Let the colorspace change settle before WGC creates its capture item / detects HDR.
                     std::thread::sleep(std::time::Duration::from_millis(250));
                 }
             }
+        }
         let relay = HelperRelay::spawn(
             &target,
             (mode.width, mode.height, effective_hz),
@@ -2466,6 +2470,10 @@ fn virtual_stream_relay(
     // decoder must resume on a keyframe — the two encoders keep independent infinite-GOP state).
     let mut dda: Option<DdaPipe> = None;
     let mut on_secure = false;
+    // Whether we dropped the SudoVDA out of HDR for the secure (DDA) leg, so we know to restore it on
+    // the way back. Keyed off the monitor's REAL HDR state at the moment of the switch (a user can
+    // toggle Windows HDR mid-session), not the handshake bit depth.
+    let mut dropped_hdr_for_secure = false;
     let mut next = std::time::Instant::now();
     let mut await_idr = false;
     // Step 6 relaunch watchdog: how many times in a row the helper has died without producing a frame.
@@ -2557,10 +2565,13 @@ fn virtual_stream_relay(
             if secure {
                 // SDR-while-secure (HDR sessions ONLY): drop the SudoVDA out of HDR so the secure
                 // (Winlogon) desktop renders SDR/composed — HDR fullscreen independent-flip is what made
-                // DDA storm ACCESS_LOST (black). For an SDR (8-bit) session the output is already SDR, so
+                // DDA storm ACCESS_LOST (black). Key off the monitor's REAL HDR state (a user may have
-                // toggling is a needless topology change AND its matching restore on the way back would
+                // toggled Windows HDR on the virtual display), not the negotiated bit depth — the pipeline
-                // force the desktop into HDR the 8-bit encoder can't take (broken image).
+                // streams HDR whenever the monitor is HDR regardless of the 8/10 handshake. For an SDR
-                if bit_depth >= 10 {
+                // monitor this is a no-op (no needless topology change, nothing to restore).
+                dropped_hdr_for_secure =
+                    unsafe { crate::vdisplay::sudovda::advanced_color_enabled(target.target_id) };
+                if dropped_hdr_for_secure {
                     let toggled = unsafe {
                         crate::vdisplay::sudovda::set_advanced_color(target.target_id, false)
                     };
@@ -2590,10 +2601,11 @@ fn virtual_stream_relay(
                 dda = None; // free the secure DDA encoder; the relay (helper) is the source again
                 while relay.try_recv().is_ok() {} // drop secure-dwell backlog
                 relay.request_keyframe(); // client decoder resumes on the helper's next IDR
-                if bit_depth >= 10 {
+                if dropped_hdr_for_secure {
-                    // HDR session ONLY: the secure switch dropped the SudoVDA to SDR for the DDA leg, so
+                    // We dropped the SudoVDA to SDR for the DDA leg → restore HDR AND rebuild the helper
-                    // here we must restore HDR AND rebuild the helper so WGC re-detects the HDR
+                    // so WGC re-detects the HDR colorspace. (An SDR session never changed the colorspace
-                    // colorspace. An SDR session never changed the colorspace → no rebuild, no recreate.
+                    // → dropped_hdr_for_secure is false → no rebuild, no recreate.)
+                    dropped_hdr_for_secure = false;
                     unsafe {
                         crate::vdisplay::sudovda::set_advanced_color(target.target_id, true);
                     }

crates/punktfunk-host/src/vdisplay/sudovda.rs

@@ -23,11 +23,11 @@ use windows::Win32::Devices::DeviceAndDriverInstallation::{
 };
 use windows::Win32::Devices::Display::{
     DisplayConfigGetDeviceInfo, DisplayConfigSetDeviceInfo, GetDisplayConfigBufferSizes,
-    QueryDisplayConfig, SetDisplayConfig, DISPLAYCONFIG_DEVICE_INFO_GET_SOURCE_NAME,
+    QueryDisplayConfig, SetDisplayConfig, DISPLAYCONFIG_DEVICE_INFO_GET_ADVANCED_COLOR_INFO,
-    DISPLAYCONFIG_DEVICE_INFO_SET_ADVANCED_COLOR_STATE, DISPLAYCONFIG_MODE_INFO,
+    DISPLAYCONFIG_DEVICE_INFO_GET_SOURCE_NAME, DISPLAYCONFIG_DEVICE_INFO_SET_ADVANCED_COLOR_STATE,
-    DISPLAYCONFIG_PATH_INFO, DISPLAYCONFIG_SET_ADVANCED_COLOR_STATE,
+    DISPLAYCONFIG_GET_ADVANCED_COLOR_INFO, DISPLAYCONFIG_MODE_INFO, DISPLAYCONFIG_PATH_INFO,
-    DISPLAYCONFIG_SOURCE_DEVICE_NAME, QDC_ONLY_ACTIVE_PATHS, SDC_ALLOW_CHANGES, SDC_APPLY,
+    DISPLAYCONFIG_SET_ADVANCED_COLOR_STATE, DISPLAYCONFIG_SOURCE_DEVICE_NAME,
-    SDC_USE_SUPPLIED_DISPLAY_CONFIG,
+    QDC_ONLY_ACTIVE_PATHS, SDC_ALLOW_CHANGES, SDC_APPLY, SDC_USE_SUPPLIED_DISPLAY_CONFIG,
 };
 use windows::Win32::Foundation::{CloseHandle, HANDLE, LUID};
 use windows::Win32::Graphics::Gdi::{
@@ -276,6 +276,48 @@ pub(crate) unsafe fn set_advanced_color(target_id: u32, enable: bool) -> bool {
     false
 }
 
+/// Read the SudoVDA target's CURRENT advanced-color (HDR) state via the CCD API — i.e. whether HDR is
+/// actually ON for the virtual display right now (e.g. because the user toggled it in Windows display
+/// settings). The capture/encode pipeline follows the monitor's real colorspace (WGC → FP16 → NVENC
+/// Main10 BT.2020 PQ), so this is the authoritative "is this an HDR session" signal — NOT the
+/// handshake-negotiated bit depth. Returns false if the target isn't found / the query fails.
+pub(crate) unsafe fn advanced_color_enabled(target_id: u32) -> bool {
+    let mut np = 0u32;
+    let mut nm = 0u32;
+    if GetDisplayConfigBufferSizes(QDC_ONLY_ACTIVE_PATHS, &mut np, &mut nm).is_err() {
+        return false;
+    }
+    let mut paths = vec![DISPLAYCONFIG_PATH_INFO::default(); np as usize];
+    let mut modes = vec![DISPLAYCONFIG_MODE_INFO::default(); nm as usize];
+    if QueryDisplayConfig(
+        QDC_ONLY_ACTIVE_PATHS,
+        &mut np,
+        paths.as_mut_ptr(),
+        &mut nm,
+        modes.as_mut_ptr(),
+        None,
+    )
+    .is_err()
+    {
+        return false;
+    }
+    for p in paths.iter().take(np as usize) {
+        if p.targetInfo.id == target_id {
+            let mut info = DISPLAYCONFIG_GET_ADVANCED_COLOR_INFO::default();
+            info.header.r#type = DISPLAYCONFIG_DEVICE_INFO_GET_ADVANCED_COLOR_INFO;
+            info.header.size = size_of::<DISPLAYCONFIG_GET_ADVANCED_COLOR_INFO>() as u32;
+            info.header.adapterId = p.targetInfo.adapterId;
+            info.header.id = p.targetInfo.id;
+            if DisplayConfigGetDeviceInfo(&mut info.header) == 0 {
+                // value bit 1 = advancedColorEnabled (bit 0 = advancedColorSupported).
+                return (info.Anonymous.value & 0x2) != 0;
+            }
+            return false;
+        }
+    }
+    false
+}
+
 /// Force the freshly-added SudoVDA monitor to the client's exact `WxH@Hz`. The ADD IOCTL only
 /// ADVERTISES the mode; Windows otherwise activates an IDD target at a 1280x720 default, so the
 /// ACTIVE mode (what DXGI Desktop Duplication captures) must be set explicitly. CDS_TEST first so a