Solve the border change shenanigans when disbanding/losing cities - simple solution

[Corbeau-1]

I'm filing this as a bug even though I don't think it's a result of faulty code, more of lack of realisation that such situation may arise when creating the game.

Describe the bug
See image.

The three exclaves were created when cities were disbanded.

What happens right now is the following: when national borders are switched on, the moment the city is gone, all tiles it controls are reverted to neutral. Then, at TC, if cities of both neighbouring nations are in range of the tile(s), it is my guess that whichever nation is computed first, gets the tiles as its own territory. So, this would mean that you have 50% of chance to lose it or to get it back.

To Reproduce
Any situation where a city is removed: spontaneous migration, building a population unit, military destruction, starvation.

Expected behavior
There are many possible solutions, but the simplest patch may be:
When the city is gone, retain present border situation until TC
At TC:
If the tile is within working radius of any the previous owner's cities, the previous owner keeps them.
else
If the city was conquered and the tile is in range of the conquering nation, it becomes its property and the border moves
else
if there was no conquest (meaning, city was peacefully disbanded or starved) OR the tile is not withing working radius of the conqueror's cities, other neighbouring nations compete for the tile using current mechanic (TC sequence, random order)
else
the tile becomes neutral

[Corbeau-1]

Here's another example:

[lmoureaux]

Tiles worked by a city should never be transferred to another nation, maybe this is the reason? Were the tiles within the city working radius at the time?

[Corbeau-1]

I can't know for sure, but it seems very logical to assume that the tiles in question were worked by the disbanded city. Once the city was gone, the tiles were no longer worked and were able to be taken.

If this is the case, then yes, I guess this can be worked around by a "gentlemen's agreement" that such tiles will not be "invaded by foreign workers". But, for one, this agreement may not always be agreed on and, for two, it depends on who gets online first an if the foreign city grew and automatically rearranged workers to "invade" the now available tiles.

edit: I just realised that I wasn't clear about what exactly is happening. When the city disbands on TC, the tiles become neutral for the whole turn and border change happens on the next turn. So in some cases the "home" player can prevent this by getting his workers to work those tiles. But it's not always possible for reasons stated above.

Another aspect of this problem is, when conquering, tiles becoming neutral immediately removes restrictinfra and makes it possible to attack further, sometimes even going directly to the next city.