On the river holding 46 in big blind

Folds around to button who just limps. Action was limp check in blinds early stages of live tourney.
Flop A96 rainbow. Check check check
Turn is a 4. Btn check, SB pauses and bets, I call, btn folds.
River another 4. Flush doesn't complete. Check, bet, reraise for 3/4 my stack. I'm all in here for tourney life. SB Villian shows AK for aces up with K kicker and tosses it in.

Analysis options at turn?
I've been agressive so I'm thinking SB was waiting for my raise pre. Any thoughts. Do you ever just call reraise on river conserving 1/4 stack?

(this is precisely why you don't flat AK in the SB to a button limp )

close between tapping accelerator on the turn or the river. bottom two pair is vulnerable to counterfeit, so i don't mind flatting and raising non A/9 rivers. SB will give value either way and you keep some bluffs in range with a call turn, raise river line also.

take c/c line also if BTN raises. (c/r actual 4 river)

You don't say how much the entry is for the tourney. But in most tourneys I am shoving on the river for the last 1/4 of my stack with the intent of rebuying if i don't double up. I think it is extremely unlikely villain has AA or even 99. Villain can have A4 but there are only 3 combos. AK/A9/A6 have 30 combos.

Also, I am raising the turn here. You don't say if the 4 on the turn puts out a flush possibility but there are too many rivers that complete straights. I'd rather have it heads up or take it down with bottom two.

I don't get how the BTN checks the turn. But if he checked in error then I think that it makes it more likely that the BTN has a gutter or straight draw.

Thanks for input. Old silver and Mr Rick.

I dont like the limp by the button. My hand is weak so I only called but I contemplate raise here with a pair or AQ + even A10 sometimes. The deck was cold for his AK. The button holdings could of been 9 10 light with the fold in position but maybe missed given action. I charge flush draws here? Even though I'm not putting him on any Ace with limp. I'm going for max value with river bluff raise and I am lucky with full house but I call most sizings with 2 pair unless it counterfeits my 2 pair. The ace on the river would be a tricky card and I have to let go often especially if flush completes as in the draw was there of course as I stated FD missed. Best of luck at the table sand may the cards run in your favor. .