As long as a character doesn't lose game abilities, doesn't use another game ability, or break the roleplay physical requirements of refitting armor, they are not interrupted. At the end of the focus period, the armor would be fully repaired to it's maximum armor amount, regardless of it's starting value or anything that happened during the focus period.
We realize that it doesn't conceptually makes sense that you can be hit with a shatter at 59 seconds of refitting and then have a fully repaired set of armor at 60 seconds but this is a representative game.