- Seed s_up from WiFi.status() in net_guard_start so the first
STA_GOT_IP (fired during setup's busy-wait, before onEvent was
registered) is not missed — prevents a reconnect flap on every boot.
- Drop WiFi.disconnect() from net_guard_tick; WiFi.begin() alone
re-associates cleanly and avoids a spurious STA_DISCONNECTED that
was double-logging EVT_WIFI_DOWN on every retry.
- Re-check s_up after the millis() timing gate to close the
GOT_IP-vs-tick race.
- Document the volatile-only shared-state contract.
Peter Woolery
84d9ba349b