Using Foldaside 100 track where all 4 doors fold to 1 side, what keeps the doors flat in the closed position, do they “snap” closed with springs on the hangers in the track or do they have to be bolted to the floor?

The Foldaside 100 kits are supplied with flush bolts to keep the doors in place when open flat.  The 4 door kit comes with 2 flush bolts which would be positioned at the top of the doors, possibly the end of leaf 1 & 3 (or 2 & 4) and either bolted into the track, or aside the track depending on your door thickness etc.