`time.After(ProbeTimeout)` returned a single channel shared by every
probe goroutine in the cycle. Only the first goroutine to receive the
deadline tick drains the channel; any other goroutine still waiting on
its `responseCh` is then stuck forever, `wg.Wait()` never returns, and
the scheduler loop in `app.go` stalls on the next tick. The condition
fires whenever two or more nodes time out in the same cycle — common
under cable-pull where IsOnline lags reality and both routers stay in
the candidate set as half-open TCP.
Move the timer inside each goroutine so every probe has its own
deadline.
Updates #3234
Replace routes.PrimaryRoutes reads with NodeStore. Connect bumps
SessionEpoch; Disconnect re-checks it inside UpdateNode so the
check and mutation are atomic against a concurrent Connect on
the same node.
The connect_race regression test is carried in its final
SessionEpoch form.
Updates #3203
Ping HA subnet routers each probe cycle and mark unresponsive nodes
unhealthy. Reconnecting a node clears its unhealthy state since the
fresh Noise session proves basic connectivity.
Updates #2129
Updates #2902
