MRUK queryCompleteEvent error -2 on Horizon OS v203

Hardware/software:
- Quest 3, Horizon OS v203 (PTC, displayed as "v2.3")
- Spatial Persistence Service: Version 84, Build Apr 19 2026
- Meta Quest Link PC app: v201 (MQDH reports persistent version 
  mismatch)
- Unity 6000.3.14f1
- Meta XR SDKs tried: v201.0.0 (Asset Store latest) and v85.0.0 
  (resolves to OVRPlugin 1.117 / SDK 1.1.53)
- OpenXR Plugin 1.17.0, Meta Quest Support enabled (Android tab)
- Settings > Apps > Spatial data: ON

Symptom:
Every MRUK scene query in a standalone APK build returns:

  E/Unity: MRUK Shared: queryCompleteEvent->result returned error 
    code: -2
  E/OVRPlugin: [XREVENT][XR_ERROR_RUNTIME_FAILURE] 
    XR_TYPE_EVENT_DATA_SPACE_DISCOVERY_COMPLETE_META

Save operations also fail with XR_ERROR_RUNTIME_FAILURE on 
XR_TYPE_EVENT_DATA_SPACE_SAVE_COMPLETE_FB.