Prompt evolution: inherit INSTRUCTIONS, not text. G0 behavioral analysis shows efficient agents average 58 w/t but start at 45 and expand. Extracted rule: "keep contributions under 50 words." EVOLVED condition gets this instruction. CONTROL gets standard prompt. Both budget=400. P1: EVOLVED survives longer (instructions reduce word count → budget lasts). P2: F₀(EVOLVED) different from F₀(CONTROL) — instructions change structure. P3: EVOLVED words/turn < CONTROL (instruction compliance). Kill: EVOLVED same survival as CONTROL → instructions ignored/not actionable.