Here is the exposed double-ended staging track. Only one #5 turnout is hidden, in the upper left, but is reachable from the access area. The minimum diameter is O81.
And here with the elevated terrain and tracks.
Pretty hard to reach a derailment in the staging track area - no fix for that at present. But with #5 turnouts and O81 minimum, derailments SHOULD be rare 😉. Better run dead slow on entering and exiting to reduce the risk.
Alternatively, for those who are risk-averse, the staging tracks could be the (original) single-ended, and ending at the maximum reach beneath the elevated scenery, from the upper-left access area.
There could be an opening in the level foundation in the lower-left corner, to allow a person beneath the layout, to reach the hidden staging tracks. Not fun, but might work out, perhaps better than nothing.
Perhaps a board with indicator lights, to show how far a train has advanced in each staging track, will help.
Perhaps a grabber stationed at each access area will help to extend the reach:
