Hi Scooby,
Most experienced racers WOULD anticipate a sloop rigged boat luffing an overtaking spinnaker rigged boat even though the rules do not require that as you correctly wrote. The rules also do not require the leeward boat from anticipating that the windward boat may not manoeuvre promptly in a seamanlike fashion but, again, most experienced racers WOULD so that they can be ready for the consequences (read rule 14). I hope this helps.
Where in the rules does it state a boat has to anticipate what another might do and PLAN for avoiding action?
You state yourself that the wording is “promptly”; not “anticipate”
IF I got into the position(and I would try not to, remember I am playing devils advocate), I would still be saying “to manoeuvre promptly, the first thing I will need to do is PROPTLY drop my Spi ONCE THE LUFF HAS STARTED”
