An interface is always compiled in, so it has complete access to the game state. However, if your version of Xconq has any networking support, the interface should not modify kernel structures directly, but should instead use the networking-enabled kernel modification routines. The kernel routines will forward any state modifications to all other programs participating in a game, so that everybody's state remains consistent.
A working interface must provide some level of capability in each of these areas:
The file `skelconq.c' in the `kernel' directory is a good example of a minimum working interface.
Don't let interfaces ever set kernel object values directly, always go through calls that can be "siphoned" for networking.