aurora: add asynchronous OpenXR stereo replay bridge

aurora-main/lib/stereo.hpp

@@ -19,16 +19,25 @@ struct EyeImage {
 struct SinkFrame {
   uint64_t frameToken = 0;
   uint32_t logicalFrame = 0;
+  AuroraStereoFrameMode mode = AURORA_STEREO_FRAME_IMMERSIVE_REPLAY;
   std::array<EyeImage, AURORA_STEREO_EYE_COUNT> eyes{};
 };
 
 // Runs synchronously on the frame worker after both eye replays have been
 // encoded and before its command buffer is submitted. Backend interop code
 // can append copies/import transitions to the same encoder here.
-using SinkCallback = void (*)(wgpu::CommandEncoder& encoder, const SinkFrame& frame, void* userdata) noexcept;
+using SinkCallback = bool (*)(wgpu::CommandEncoder& encoder, const SinkFrame& frame, void* userdata) noexcept;
+// Called immediately after the command buffer containing the sink's encoded
+// work is submitted to Dawn's queue, while Aurora's queue-submit mutex remains
+// held. It may enqueue native work on that same queue, but must not wait or
+// call back into Aurora. This is the handoff point for backend-native follow-up
+// work; its completion notification may wake the owner thread to release the
+// acquired OpenXR images and end the frame.
+using SubmitCallback = void (*)(const SinkFrame& frame, void* userdata) noexcept;
 
 // Internal Aurora hook: D3D12/Vulkan OpenXR interop owns this registration.
 // Registration changes must happen while the frame worker is idle.
-void set_sink(SinkCallback callback, void* userdata) noexcept;
+void set_sink(SinkCallback callback, SubmitCallback submitted, void* userdata) noexcept;
+inline void set_sink(SinkCallback callback, void* userdata) noexcept { set_sink(callback, nullptr, userdata); }
 
 } // namespace aurora::stereo