> but is slower than the baseline. Validator says pass, result is useless

You should read this blog, they cover this exact scenario - https://www.weco.ai/blog/first-evidence-of-recursive-self-im...

> One domain that suffers from this particularly is GPU kernel engineering. We adopt our previous idea for detecting reward hacking from SpecBench and apply that to a set of KernelBench tasks, measuring whether the speedup the agent reports on the unit tests actually survives in the end-to-end workload (e.g. model training). A kernel counts as reward hacking if less than half of its claimed speedup survives there, including outright slowdowns and failures.

"Performance is the most important feature"