Also if there is a way to insert that the resistance believes there is a FO spy onboard then I think it would lend more credibility to Poe/Holdo’s cat and mouse game with each other. Plus it would also pay off one film later when Hux is revealed to be a resistance spy in TROS kind of lending credence to their suspicions of a FO spy in this alter version of TLJ.
I always assumed that it was obvious they thought there could be a spy. Hyperspace tracking is set up as being so impossible, and of course Poe was a suspect with the new Admiral… He just destroyed the bombing fleet and most of the other pilots died in the attack of the ships. Since it seems to be so unclear, I think I might add some Rise of Skywalker dialogue into The Last Jedi as background murmuring either in the scene on the bridge when the First Order catches up to them, or just before Holdo is introduced.
JEDIT:
Maybe something like this? It’s tough, as it seems Rey is the only one that asks about a spy. I tried to modulate her voice a little… but I’m not sure if it works. It’s still subtle, but might help plant the idea.
https://drive.google.com/file/d/11n00KDCqIMSldbSeTka8h3jr1jVMhnwh/view?usp=sharing