This would be a nice feature. Though I imagine it might be hard to implement. Maybe the fleet would stop and you get a notification when it becomes in range of an enemy fleet? Then what, manual re-routing or turn around and flee? Perhaps a simpler modification would be to avoid enemy zones of influence, though in late game that would be near impossible.

It is annoying to me as well. This is why I rely heavily on save / reload.

I find it annoying as well except that I'm thinking adding this feature/functionality would add a lot of additional processing. Consider every time a ship/fleet moves anywhere, it needs to do a check each hex. Repeat for all your ships. Repeat for every ship in the universe. Maybe this is why it wasn't added in GC3. I personally do not do auto-survey/explore as I want to see where the goodies are

The feature exists in other games and it's not that much different from the Sentinel command which puts them to sleep until an enemy enters their FOV. Enemy enters FOV=wake up, changed to Enemy enters FOV=STOP.

I would also like to see the movement changed in general, to quit doing giant check marks. In previous GCs, the ships would do a more or less straight line wiggle from A to B when A and B were not exactly in the same hex side line(1 to 4 to 1 to 4 on the hexagon, for example, draw it out and you'll see what I mean if that doesn't make sense). Now they do this huge right-angled crap that frequently either moves them into places with enemy ships or otherwise does weird things when using ships for scouting. Makes trying to map out the edges of the clusters a little annoying.

I don't think it would add a lot of additional processing.   It already needs to draw the newly spotted ship/monster when it comes into range anyway with the correct symbol, so 90% of the processing is done at that point.   All it needs to do is make an additional check as to whether it's dangerous then stop if that option is turned on.

same, except it’s probes, not colony ships.