Looplane's prompt is now `m3-exact-edit-v4`: the version persists into artifacts; core/tool/interaction/runtime/instructions/skills/workspace/memory are composed as stable or dynamic sections; and positive/negative examples cover replace_text, unified diffs, and direct replies. Unit tests pin the structure, while live-eval coverage still needs expansion.
Even with temperature=0, LLM outputs can still fluctuate by up to 15% in practice. To rigorously compare agent changes, you need a frozen golden set, at least 3 runs per query averaged out, LLM-as-judge blind evaluation (pairwise preference flip rate reaches 35%), and paired statistical tests -- not just running each version once and going by feel.
"Adding a Cross-Encoder feels better" is not a scientific evaluation. A/B testing tells you whether a change actually works, how much it helps, and which query types benefit.