The Spanwatch Lattice — As Held
Not a design — a thing built in a hurry, from whatever came home. The Doorstep was a quiet, under-mapped junction nobody watched. Then the ISV Endurance came back through it, five years lost, carrying a warning — and the door she came through will open again, on a clock measured in months. The Lattice is what a fleet throws up over a door it cannot close: a watch-array and a lock, welded together out of the Endurance's own stripped core, mismatched and asymmetric and barely holding. The drawing is marked AS-BUILT because there was no time to draw it first.
The Endurance came home to be taken apart. Her core is the heart of the lock now, and the lock is all that stands between human space and whatever follows her back through the door. In The War at the Door the blocs spend the worst week of the golden age learning to hold the Doorstep together — and what it costs to keep one improvised lattice lit until the rest of the fleet arrives.