This makes the opening of a gate an activity, so that it will be interruptable.

[jcd000]

The side-effect is that any monster beyond the gate will only see the player after the gate is opened, not during. This is because only when the activity ends, the gate is opened. There may be a way to change this to the old behaviour if:

1. The gate is opened immediately (or after, say, half the time needed to really open it)
2. A cancellation of the activity results in the gate automatically closing.
   I am against this route however.

This handles issue #11975 and the following forum topic: http://smf.cataclysmdda.com/index.php?topic=11151.0

[Rivet-the-Zombie]

This is great!

[kevingranade]

I think I see where you're coming from, cancelling after the door opens could be problematic. One thing that comes to mind is changing the door/gate/whatever to a 'half open gate' half way through the activity that allows vision and movement, but counts as difficult terrain. Obviously that's a whole new feature and isn't necessary for this pr.

[i2amroy]

One thing that comes to mind is changing the
door/gate/whatever to a 'half open gate' half way through the activity that
allows vision and movement, but counts as difficult terrain. Obviously
that's a whole new feature and isn't necessary for this pr.

This seems like probably the best thing to do IMO.