This is the part where you tell me partner has
♠QJx,
♥KQJxx,
♦Jx,
♣Jxx and opened 'a bit light, but I had to get that heart suit in'
Partner's failure to show a control in diamonds is surprising, I was expecting a singleton most of the time. I guess partner really does have the 3=5=2=3 hand (or perhaps a 2=5=2=4 with spade Ax?), presumably with concerns over the diamond suit (but we lost the minors years ago, why is this a concern?). Does this imply that partner likely holds a strong notrump?
I'll bid 4NT (RKC 1430, signing off in 5
♣ opposite one key card, bidding small slam opposite two, looking for a grand opposite three). We've passed the point of no return facing zero. If I am playing 0314 with clubs as trumps (as I used to) I will bid 4
♠ last train instead and pray partner does not sign off with two key cards.
It is very possible that 5
♣ will fail facing one key card, but we're out of bidding space. I should have added that I play a 4NT response to 4
♣ as regressive.