[amorphic]

I second this approach.

I often find myself in similar situations as OP's, working with a client to understand a complex or ill-defined problem space and developing solutions in an agile way.

Neither you nor the client has a (functioning) crystal ball and so all that you can do is make the best decisions that you can with the information available at the time.

I've found that documenting Architectural Decisions as Architectural Decision Records (ADRs) helps build a shared understanding and ownership of these decisions amongst all concerned. They also prevent me from becoming bogged down and second-guessing myself: Here are the available options, here's what we decided and here's why.

No need to make ADRs overly long or complex. I use this "Lightweight" template:

https://github.com/peter-evans/lightweight-architecture-deci...