Do I need to protect all wiring in an attic when adding a permanent ladder?
I have never had an AHJ confront me about exposed romex in an attic with or without a permanent ladder. One quick note though, if you are laying down plywood Make sure there are no electrical cables laying across the joist where they may be pinched and shorted. Notch the joist and use nail plates or reroute the cables.

Good luck