Howdy Belter,
Your moves, your turn, always resolves before you make the Threat Move. Check Gas, Character Action, Threat. So when you decide to move into the airlock, check your gas, then move your pawn and resolve your action as normal. When that action's done, then you draw for your boogin. Means you can decide to be done and hit the breakaway switch before that haint has a moment to move in, if you want. But if it does reach your airlock, it makes itself cozy. No more AI movement for the Ghostie-goo, at least until the next time a threat is spawned. Then it'll come after you as normal. Leaving the airlock to do so.
As far as the infinite recursion loop of see the ghost in the airlock and bug out, yeah that is indeed a dilly of a pickle. If it's in there and you move into its space, you gotta steel yourself and try and deal with it as best you can. I'd suggest generous application of Grit and Gear. Also, if your ship's hainted and constantly dropping Ghosts on you, I'd recommend selling it and getting yourself a new bird. New cargo compartment without all the ghosts and such. Powerful expensive fix, but sometimes it's worth it.
If ever there's a question of simultaneous moves, rule of thumb is Player agency resolves before fallout. Then fallout, then threats. If it's two players that are tied in knots, initiator has right of way.
Clear as mud? Hope something in there's helpful to you, and if it isn't, ping me back and I'll see if I can't fix that.
Chariot, out.