Prefer OpenXR for desktop XR policy

docs/modernization/roadmap.md

@@ -336,7 +336,8 @@ Implementation tasks:
   - `glad`
   - `Catch2`
 - Keep vendored until proven:
-  - OpenVR
+  - OpenVR only as the temporary desktop compatibility fallback while OpenXR is
+    introduced behind `pp_platform_vr`
   - OVR/Wave SDKs
   - Wacom WinTab
   - AppCenter
@@ -735,9 +736,11 @@ VR mode, VR-controller, auto-timelapse, and cursor-mode side effects through
 retained settings writes, recording lifecycle calls, and legacy canvas/UI
 adapters continue.
 VR mode start/stop now enters `App` platform wrappers that dispatch through
-`PlatformServices`; Windows keeps the retained OpenVR bridge in
-`WindowsPlatformServices`, while the legacy fallback reports unsupported VR
-startup on non-Windows platforms until their shells own the service.
+`PlatformServices`; the desktop runtime-selection policy in `pp_platform_api`
+prefers OpenXR and marks OpenVR as a legacy fallback. Windows still reaches the
+retained OpenVR bridge in `WindowsPlatformServices` until the OpenXR backend is
+wired, while the legacy fallback reports unsupported VR startup on non-Windows
+platforms until their shells own the service.
 `pano_cli plan-about-menu` exposes app-core planning for About menu help,
 about, what's-new, crash-test, and performance-test commands, including
 versioned what's-new labels, diagnostic gating, and no-canvas performance-test
@@ -823,8 +826,9 @@ available and dispatches startup through the same service, preserving the
 current iOS Objective-C bridge in the legacy adapter while removing iOS branches
 from `App::init_menu_tools` and `LegacyToolsMenuServices`.
 App VR lifecycle start/stop now asks `PlatformServices`, preserving the current
-Windows OpenVR startup/shutdown bridge in `WindowsPlatformServices` while
-non-Windows fallback adapters keep the existing unsupported/no-op behavior.
+Windows OpenVR startup/shutdown bridge as the selected legacy fallback in
+`WindowsPlatformServices` while non-Windows fallback adapters keep the existing
+unsupported/no-op behavior.
 Canvas image export publishing and explicit persistent-storage flushes now
 dispatch through `PlatformServices` too, preserving iOS photo-library export
 publication and WebGL filesystem sync behavior in the legacy adapter while
@@ -903,8 +907,8 @@ the live OpenGL call sequence. The retained viewport/scissor callback endpoints
 now share `legacy_ui_gl_dispatch`.
 VR UI framebuffer viewport and scissor-test setup now also consumes those
 `pp_renderer_gl` contracts, keeping desktop and VR UI rendering aligned while
-the retained OpenVR app path is split incrementally; its retained callback
-endpoints now reuse the shared UI GL bridge.
+the desktop XR path moves from the retained OpenVR app path toward OpenXR; its
+retained callback endpoints now reuse the shared UI GL bridge.
 VR draw blend/depth state snapshots, transitions, restore, and depth-buffer
 clears, active texture unit switches, and fallback 2D texture unbinds now use
 generic tested `pp_renderer_gl` capability query/apply, clear, active-texture,
@@ -2699,7 +2703,8 @@ Use this as the starting checklist for Phase 0 inventory.
   VR controllers.
 - Platform services: clipboard, file picker, save picker, directory picker,
   share/display file, keyboard show/hide, cursor visibility.
-- VR/platform variants: OpenVR desktop, Quest, Focus/Wave, Android standard,
+- VR/platform variants: OpenXR desktop target with retained OpenVR fallback,
+  Quest, Focus/Wave, Android standard,
   iOS/macOS, Linux, WebGL.
 - Cloud/network: upload, download, browse, license/check flows.
 - Recording/export: PBO readbacks, MP4 encoder, timelapse frames.