I had an idea while playing. Currently there are 2 icons that exist above the END TURN circle, one to cycle through idle fleets and one to execute planned fleet movements. Perhaps a third icon could be added that would cycle through threatened fleets having an action point to spend. By threatened fleet, I mean any fleets that share star system orbit with a hostile enemy fleet. This could serve the purpose of notifying a player when an enemy fleet moves into orbit (instead of just moving into visibility range which, as a workaround, doesn't address the actual issue being discussed) and keeping a player informed of potentially unused action points during ongoing skirmishes with many fleets.

Please note: This would mean adding a binary system that creates a fleet status of Threatened or Not Threatened. The specifics of such a system could include or exclude, or grant the option to include or exclude, exploration fleets and/or colonization fleets.

Considering my concern relates to Single-Player, I appreciate your feedback, but the lack of an active effect to multiplayer end turn exploits should not be an argument to not implement fixes that would benefit everyone in every other scenario which would be affected by such a change.