The marginal A1S cradle contact flickers open mid-call; treating a
brief open as a hangup dropped the live conversation. Raise the
prolonged-open hangup threshold to 2.5 s and make the resync
asymmetric: a PICKUP is confirmed fast (600 ms, calls answer promptly)
while a HANGUP needs the line to stay open 2.5 s. Brief flickers no
longer end the call; a real hangup still fires ~2.5 s later.
clement