This sounds really interesting, I'm looking forward to reading the comments here in detail and looking at the project, might even end up incorporating it into my own!
I'm working on something that addresses the same problem in a different way, the problem of constraining or delineating the specifically non-deterministic behavior one wants to involve in a complex workflow. Your approach is interesting and has a lot of conceptual overlap with mine, regarding things like strictly defining compliance criteria and rejecting noncompliant outputs, and chaining discrete steps into a packaged kind of "super step" that integrates non-deterministic substeps into a somewhat more deterministic output, etc.
How involved was it to build it to comply with the OpenAI API format? I haven't looked into that myself but may.