Ideally Id like to ask west:
Have you got the AS? How many spades have you? How many diamonds? Have you got the KC? How solid are your red suits?
It would be lovely if we avoid a bad slam missing AS, a spade ruff, trump loser (ruffing out the Ds could expose that) and missing/bad placed KC, but I cant find all that out
After the 3D Im forcing 3S again- I doubt if west can bid 3N but Im interested in more shape information, then the Black...
There could be a problem using the RKCB that you suggested next, but sometimes a problem can offer a neat solution too!
When I bid 4N west will have to rely on the general agreement that without express agreement to a suit {we havent actually agreed hearts} Ill assume that you are RKCB in the last suit bid and if it went 3S-4C-4N then 5H now shows west the AS and the KC, making 7H a real goer
Failing that at least you can make a reasonable judgement of contract and level, without trying to ride a bicycle backwards as happens after opening weak in first position and then back-pedalling
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Bon chance!