On the river facing a small bet with A-high and no spade, we should call given the price and solver’s mixed strategy.
K85ss is a semi-wet texture that SB defends well against. Solver prefers a small c-bet or checking range here, but a medium c-bet like 3.1BB is still reasonable. We’re betting A-high with backdoor nut flush potential and some fold equity versus SB’s weaker holdings.
Turn Td is a dry card that doesn’t change much; SB still has plenty of Kx, 8x, 5x, and spade draws. With SPR ~2.5 and A-high, we can either bet large or check. Solver leans toward checking, but a big barrel is reasonable as a bluff to pressure one-pair hands and draws.
River Kh pairs the board and SB now has a range advantage; after we check, SB’s 6.8BB bet into 19.2BB gives us ~2.8:1, needing ~26% equity. Solver mixes call/fold here, but A4o with no spade has enough equity to justify a call. Folding gives up too much equity versus a range that still contains some bluffs and thin value.
Note: Folding A-high to a small river bet with ~2.8:1 odds gives up too much equity; solver mixes call/fold, and A4o with no spade has enough equity to continue.