One monitored subscriber endpoint (W3b.5 age contracts). Separate
table from MonitorSpec — sub contracts key different endpoints
and need no publish counter.
One contracted publisher’s counters. Baked as a static by codegen
(or declared by the fixture); the publisher handle bumps count on
every publish, the executor reads deltas on spin ticks.
One contracted subscriber’s take-age accumulator (W3b.5). The take
path records epoch_now - header.stamp per message (fetch_max); the
age check drains it (swap 0) per window.