I think I slightly prefer a 3-bet here since villain is likely to be fairly wide when isoing, and their range will contain a lot of dominated Ax/broadways. Calling is okay though.

River is a really tough spot. I think based on the fact that it’s the UTG limper who jams, we can make the logical assumption that this player is less likely to be capable of significant aggression here, since players who limp a lot are rarely going to take aggressive river lines.

As a consequence, it really comes down to a) do we think river can ever jam river with something like A8 here, b) what kind of potential bluffing hands can villain have, and c) how likely is it that villain might slowplay KJ or play J9 this way.

With a), I think it’s unlikely, especially since we block A8 (as well as Q8). Villain has very few potential bluffing hands that get to this river, since they aren’t likely to call turn with a lot of air hands, so that covers b). With c), I definitely think both options are very plausible. Players who do a lot of preflop limping also like to slowplay post, and J9s is a hand villain very well might play exactly this way with a high frequency.

I think you made a good fold here. I think you get shown a straight of some kind here more often than anything else if you call.