Agents stop rewriting behavior: falsifiable environment rules lift reactor-lab completion from 0% to 83%
EvoBelief writes an agent's knowledge of its environment as falsifiable hypotheses, and only rules that survive independent evidence may change predictions or plans, while the language model stays frozen. On ALFWorld without actor-side transition memory it raises success over the matched Frozen World Model by 23.9% with Claude Haiku 4.5 and 31.3% with GPT-5.4; in DiscoveryWorld's Reactor Lab it completes 83.3% of Normal-tier and 58.3% of Challenge-tier instances, versus 0% for each evaluated baseline.