ckpool patch 0004 now bounds generator_submitblock's wait for a live
primary to ~3s rather than spinning indefinitely, and calls submit
before writing the pending-block hex to disk so the happy path adds
zero latency. The right default is small: a fallback should kick in
while the work is still relevant for the current chain tip.
Range widened to [1, 600] so impatient operators can crank further
down. Description updated to reflect the new architecture.