feat(08.1-01): implement CH contraction core — ordering, contraction, overlay witness, CSR (GREEN)
- contractGraph: greedy edgeDifference + λ·deletedNeighbours priority,
lazy PQ with id tie-breaks, rank = contraction position (total order)
- overlay-only witness search: contracted node + candidate absent,
bounded by candidate distance and max(60, 4·localDegree) settles
- directed shortcut emission (ascending from, then to), via midpoints,
f32 CSR; dominated-insert guard; explosion tripwire fails loud at 4×N
- deterministic: no PRNG/map-order; identical input -> identical output
- 25-node grid: 41 shortcuts (1.64/node), 0 budget hits
araharah-executor
f75dc9e8c6