This is wild timing - I literally just used Opus 4.6 this morning to help me build my second product (guided meditation app with voice customization). The level of architectural thinking it brought to the Rails structure was way beyond what I expected.

What blows me away about your STL reverse-engineering example is that Claude didn't just brute-force the reconstruction - it built a methodology. The z-level analysis, cross-section decomposition, the reusable toolkit... that's systems thinking, not pattern matching.

I'm curious: did you iterate on the SPEC.md prompt at all, or did it nail the approach on the first try? I find that when I give Claude a clear success metric (like your "0.1mm accuracy" requirement), it gets way more creative with its solution path.

Also, the fact that it documented its own process in SKILL.md is chef's kiss. I've been building a similar approach for my own projects - having Claude create reusable "skills" that improve over time feels like we're accidentally stumbling into something bigger than just code generation.

Great write-up mate! The "chimpanzee with a stick" analogy is perfect - we're watching tool use emerge in real-time.