MoRCA Filtering of Seeded Wrong-Answer Propagation in Qwen3-0.6B Agents

When language-model agents exchange answers, one erroneous claim can return as apparent corroboration. We test whether a task-conditioned communication gate limits this failure in a three-agent Qwen3-0.6B network. Four fixed conditions cover independent agents, externally supplied correct messages, a seeded wrong-answer ring, and a structural cycle without causal return. The proposed severity score combines a harmful message marginal with directed path topology, intervention-based return fidelity, and a Möbius interaction deficit. A gate delivers messages with probability w = (1 + 3S)−1. On 64 held-out seeded-error tasks, accuracy increases from 48/64 without filtering to 55/64 with gating (paired two-sided exact McNemar p = 0.015625). Expected-token-matched random filtering reaches 53/64, not significantly different from MoRCA (p = 0.6875, exploratory). Every measured return-fidelity score is zero, so the tested gate reduces to harmful-marginal filtering. The experiment supports a narrow reliability result under seeded misinformation but does not establish an advantage for the complete mathematical construction or demonstrate collusion detection. A follow-up test must produce verified causal returns before evaluating the proposed interaction.