maybe im wrong with my impression of what an async tx is

There is some message, addressed to a smart contract.
Once all previous messages in queue have been processed, that message initiates a transaction.
Transaction launches contract and determines its response to incoming message: what it sends out and how it changes its persistent storage.
Outgoing actions are validated, balance is updated, and
outgoing messages are added into queue to be processed later.

that helps. but what if it reverts

does it have to send a message back to the first contract telling it that it was reverted?

@pcrafter thanks for the lesson. I will chew on this stuff and come back when I’m ready for more. Most appreciated

Yes, that's called bouncing. Sender may set that it's not interested in bounces, though. Offchain, that's represented by having destination address converted to unbounceable format (UQ...)

Bonus question

So I guess there has to be a gas transaction that is passed around to all the message receivers in the chain. Appears to be passed via the forward fee field in the message. How do you calculate the gas required for the enitre tx when it spans multiple messages?

Transaction in TON, 🎉 :tada:, by definition spans one message — one that initiated it.
How gas is calculated? Sender passes some TON, they're spent for computation and usually whatever remains is forwarded to the next message (contract may instead send a fixed amount, or its entire balance, or something like that; that's based on SendMode).

ok yeah i saw some refund transactions so i guess thats the roundabout way to deal with it too