I do not seem to be able to reopen the original issue (#952), so filing a new one now that we have independent sets of enabled features on an XR device & on an XRSession.

If my read of the spec is correct, the Permissions API will only return permission status for the device features (which may be persistent across sessions and do not really say anything about the state of the session), so the apps have no way of observing the contents of XRSession's set of enabled features.

My preferred way to solve this would be extending the XRSession to expose a set of enabled features. Spec-wise, it seems it could be achieved by turning the not-IDL-exposed XRSession/set of enabled features into an IDL-exposed attribute. XRSession.enabledFeatures of type set<DOMString> (or set<any>, although I'm not sure why DOMString wouldn't be sufficient here).

Related issues:
immersive-web/real-world-geometry#30
immersive-web/anchors#64