Over the 1♣ opening, the 1♠ response would show at least a 4-card suit. I would read opener's 2♣ rebid as showing minimal values, with length in clubs (i would believe 6+, although a strong 5-card suit might also be possible). Responder's 2♦ would then show a second biddable suit (good 4+ length), and i'd guess that opener's rebid of 2♥ was showing a second real suit with a hand too weak for a direct reverse - which certainly seems forcing after responder seemed to be denying four hearts with his first two bids. The 3♣ rebid by responder looks like a preference back to opener's first suit, maybe indicating 3-card support - but if he was trying to sign off in a partial, he could have done that on the previous turn, rather than showing his diamonds, so it looks to me like this sequence should be game-forcing. That said, what part of this would indicate that responder holds five spades? I yield that i'm still a beginner and just learning the game, but i fail to see the basis for your assumption about responder's 5-card spade suit. Is it that with 4243 or 4342 shape, responder would have bid 'up the line' with 1♦ and let partner show a 4-card major if he had one, rebidding spades over hearts as 4th-suit forcing (or rebidding NT to deny game forcing values)? All of that aside, i do feel that without game-forcing values, there would have been no point in showing the diamond suit after spades, as responder has already showed his major, and opener denied a fit in it. The 3♣ looks like it's saying: i could have supported you last round when you showed the extra length, but i had extra values that i wanted to show - now that we've both bid out our hands, and i finally showed my support for your club suit, choose a game: 3NT with your suits firmly stopped, or 5♣ if your distribution is extreme (i can picture opener's bidding sequence on a 1516 with values too weak to directly reverse - especially considering the late heart rebid after responder denied four hearts). Of course, my interpretation is all based on natural bidding, so if there are any obscure conventions involved, that may make my view completely inaccurate.
