> Can you inspect inputs from terraform resource attributes or data sources in the procedural evaluation?

No... the high level programming language really just serves as a bridge or translation layer to a Terraform compatible JSON file. Those sorts of evaluations don’t happen to the actually plan/apply. However, you may find it useful to make direct API calls to your cloud provider in cdktf stacks. For instance, I mostly use data lookups but if I want to perform string operations on that sort of data I would use boto3 instead.