Thanks for the continued thoughts ... here is what I have found thus far... this appears to be related to converting the selection to a layer prior to the denoise operation.
If I do the sky selection, apply denoise to the selection, do deselect, there is no "trail" left on the image.
If I do the sky selection, copy the selection as a layer (ctrl-c/ctrl-v), apply denoise to the layer, do deselect, the "trail" is left on the image.
I am not done with this yet, but obviously a simple solution would be to not create the "denoise layer", which is not ideal if you want to treat the sky as a separate adjustment layer.
On ward ...
The examples of the image above are zoomed to 200%, so at that point there is no hi-res, sharpness, noiseless to be had. The edge around the tree line is one small element of the image and to be honest not that important when view at normal size. Even the denoise of the sky is not a must, but a refinement. Here is a snap of the full image: