Always start an implementation in Claude Code plan mode. It's much more comprehensive than going straight to impl. I never read their prompt for plan mode before, but it deep-dives the code, peripheral files, callsites, documentation, existing tests, etc.

You get a better solution but also a plan file that you can review. And, also important, have another agent review. I've found that Codex is really good at reviewing plans.

I have an AGENTS.md prompt that explains that plan file review involves ranking the top findings by severity, explaining the impact, and recommending a fix to each one. And finally recommend a simpler directional pivot if one exists for the plan.

So, start the plan in Claude Code, type "Review this plan: <path>" in Codex (or another Claude Code agent), and cycle the findings back into Claude Code to refine the plan. When the plan is updated, write "Plan updated" to the reviewer agent.

You should get much better results with this capable of much better arch-level changes rather than narrow topical solutions.

If that's still not working sufficiently for you, maybe you could use more support, like a type-system and more goals in AGENTS.md?