Correction taken! To be absolutely 100% honest, I think I had failed to select all the animations before I did Export->fbx file. I tried it again, opened the entire tree of armature, meshes, and animations, selected them all, and re-exported from Blender. I reimported the updated fbx into UE4, and there were my single frame animations of open and closed states. I associated them with the quiescent states in the AnimGraph and viola, it worked!
OK, so it was a dumb mistake. Full confession!
I’m sure there is a more efficient way to pass the animations. In fact, I bet there’s a way to do what I wanted with just one animation, accessed differently in UE4 AnimGraph. For example, run the open animation in reverse for close. Specify the first and last frame, and use those frames in the AnimGraph for open and close state. That would be far more elegant and efficient, but efficiency of workflow is for another day (unless you have it off the top of your head 