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The first one, is it clear to rebid JT9xx of spades? It works well when you can see partner's hand and he happens to have AKQ, but I would expect partner to raise with Hx a lot.
Having opener raise with Hx is not a bad thing. In a DealMaster simulation opposite responder's hand with opener 2=4=5-2 with a game force with Ax, Kx, or Qx in spades, 4S made 83% of the time and 3NT made 83% of the time. I.e., it's a wash.
The only plausible other bid to me is 3NT, which opener will pass whether he is 3=4=5=1 or 1=4=5=3 or 2=4=5=2.
- If opener is 2-2 and has at least Hx in spades, it makes no difference what you bid 3S or 3N.
- If opener has 1 spade and 3 clubs, you reach 3NT.
- But if Opener is 3=4=5=1, Dealmaster says you will make 4S or more 100% of the time with 6S making 65% and 7S 16%. You will make 3N or more 84% of the time, and 6N only 7% of the time and 7NT 2%. 3S is the better bid.
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The second one, why would opener splinter with only 3
The other choice over 2S is 3S. That may be the better choice, and if opener bids that, you should still get to slam. Over 3S, resonder knows that the short suit total is 3 (1 diamond + 2 hearts = 3) so 19-21 working points takes 10 tricks and 25 working points takes 6. The combined HCP are at least 25, so a slam try is in order. If responder cue bids 4C (semi-serious rather than serious 3NT), opener will use KCB to drive to 6S.
OTOH, the SPL with only 3-card support--which is unusual--has the advantage that it helps responder evaluate his limited values correctly for slam. If responder has no HCP or wasted values in clubs, he will sign off. If he does anything else, then opener can drive to slam.