I'm assuming this list is based on https://developer.android.com/guide/topics/manifest/activity-element.html#screen, but I can't tell which mode corresponds to

portraitUp, landscapeLeft, landscapeRight

apologies if I'm missing it but can you clarify which of the modes corresponds to this combination

Just added some more docs to list what each corresponds to. For portraitUp, landscapeLeft, landscapeRight
this corresponds to user

Hmm is this from manual testing, or are you inferring from the diff between this and the fullUser docs?

Just going on the user docs, the sentence

Use the user's current preferred orientation of the handset. Corresponds to ActivityInfo.SCREEN_ORIENTATION_USER.

Does not clearly tell me that this = {portraitUp, landscapeLeft, landscapeRight}

If it is being informed by the portion from the fullUser/fullSensor docs, I'd add a note that it's not true on all devices:

This allows any of the 4 possible rotations, regardless of what the device will normally do (for example some devices won't normally use 180 degree rotation).

as this indicates to me that user/sensor won't use 180 on some devices, but WILL on others.

I am getting this from manual testing and reading the engine code. Would be it be safe to assume that if someone wanted to read more on the specifics of what 'user' value does, they would click the link in my documentation that points to the Android docs on what 'user' actually means?

Sure, I think what you've documented is reasonable and we can leave the rest to the android docs.