Agency and the ownership of personal agency--both seem so real.

Yet, I do not 'have' a brain that wills. The brain generates a sense of 'me' from competing and cooperating regions. That alone puts a double barrel shotgun to the whole question if one walks the question back to its origin, knowing that the self is little more than a bundle of senses coupled with thoughts.

Does not freewill presuppose and require sentient agency?

Go back. Go back to the root. Who or what's making the decisions in the first place, and should that being be granted a hall pass simply because it feels like a real person? Is the foundation actually solid enough to put the weight of any philosophy upon it?

Pardon me jumping in with more Oneness blather. But without an actual 'self' the whole matter dissolves back into the ground from which it came.