Yeah, I have a contract project for a webapp/integration to legacy Excel tool with an API endpoint for exchanging data with Excel. Over time, I notice issues or need to add functionality in the data processing and hadn't been closely watching the code changes Claude Code made to the API as long as it worked as expected/tests passed.

When I eventually read through the current state of the upload processing code it was like an absurd tree of checks on checks on fallbacks on triple checks added in response to whatever bug I reported in a bizarrely additive way and could be massively simplified (which would also make it less brittle to edge cases that then demanded more checks and workarounds).

The other issue is that for the upload API, there is documentation but not for every little bug or edge case so each time the model "wakes up" and loads everything into context it sees that crazy web of checks and edge cases as the only source of truth for the API so is hesitant to touch anything unless 100% necessary which then leads to more conservative behavior of additive code which makes the problem worse over time.

Codex seems a bit better but I still have to guide it towards proper abstractions/refactors to avoid that piling on cruft effect.