Reported: a 6 s auto-call gap gives clearly less than 6 s between the end of one
CQ and the start of the next.
The wait after sending watched only the keyer's busy signal. That signal travels
from the keyer to the window as an event, and the code gave it one second to
appear before giving up — if it had not arrived and cleared by then, the wait
ended immediately and the gap ran from the START of the call. A 6 s gap after a
4 s CQ becomes about 2 s of silence, which is exactly what was heard.
The message's own duration is now a FLOOR: the wait runs at least the estimated
sending time, and the busy signal only extends it (slow link, long buffer),
capped as before. The estimate can only be approximate, but it cannot be skipped
by a late event, and erring long costs a slightly wider gap rather than a call
that steps on the previous one.