I've made tests.
When you repair a keep you get X AP (in my case 120 AP per kit).
With the delve buff of 10% I get 144 AP, so a little more than +10%
Now when I eat colovian war tart buff food I get: 144 AP, so: zero AP gain.
Looks like this buff only applies to other things but not repair. Is this intentional? Could not read it in the buff food description.