Without it autoscaling builds lanes nothing routes to: autoScaleStep() writes
lanes_provisioned into the object's meta while replicaCount reads only REPLICA_COUNT.
Read off the primary's own response, never the request, since a client cannot present a lane
count. Routing to a lane that has not yet promoted is safe: it refuses until SERVING and hands
the request back, so the router needs no readiness cache.
Records the lane count a primary reported.
Without it autoscaling builds lanes nothing routes to:
autoScaleStep()writeslanes_provisionedinto the object's meta while replicaCount reads onlyREPLICA_COUNT.Read off the primary's own response, never the request, since a client cannot present a lane count. Routing to a lane that has not yet promoted is safe: it refuses until SERVING and hands the request back, so the router needs no readiness cache.