Regardless of what model you use, agentic coding tools are indeed pretty good at finding issues if you target them a bit. And they have no respect for their own code or any sense of shame. So, you can just point them at their own code with a new thread.
Many AI models seem biased to cutting corners by default when generating code, even when you ask them not to. But a few simple follow up prompts can address that. Simply ask for covering corner cases with tests, test all the known non happy paths, look for weaknesses, verify adherence to SOLID principles, do security audits, etc. It will find issues. With bigger projects, you can actually make it file those issues in gh with labels and priorities. And then you can make it iterate on fixing issues with separate PRs.
On a recent project, I made it implement a simple benchmark test for measuring throughput. I had a hunch it was doing very sub optimal things. I then asked it to look for potential performance bottlenecks and use the benchmark to verify improvements. At that point I already had a lot of end to end tests to verify correctness. So, these performance tweaks were relatively low risk. I got about two orders of magnitude improvement and a lot more graceful behavior when pushed to the limit.
If you have a bit of experience engineering systems, just treat these tools like they are junior developers. Competent but likely to skip some essential steps. So, just double check with a lot pointed questions "did you do X? If not, do it now". Anything that needs repeated asking, turn it into a guard rail / skill.
There's a bit of effort and skill involved with this. I imagine a lot of less experienced developers might struggle to get good results because they aren't asking for the right things.