The HA prober dispatches a PingRequest, waits ProbeTimeout (5s), and
marks the node unhealthy if no callback arrives. A node that bounced
its poll session between probe cycles satisfies two conditions that
conspire to fail TestHASubnetRouterFailover: a probe queued against
the previous session is silently dropped when the worker writes to
the closed connection (timeout always fires), and a probe sent
immediately after reconnect lands while wgengine is still rebuilding
magicsock state from the new netmap. Either path installs a spurious
unhealthy bit, which sends the preserved-primary anti-flap the wrong
way.
Record the session observed at dispatch time and drop the timeout
path if the node reconnected since. Require the session to survive
a full probe cycle before a timeout can drive a failover.
Restore the legacy auto-clear at write boundaries that drop HA
candidacy: Disconnect, SetApprovedRoutes(empty), and
UpdateNodeFromMapRequest shrinking advertised routes to empty.
Plus a defensive guard in SetNodeUnhealthy.
Updates #3203
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
