Beyond Update Geometry: Post-Commitment Auditing of Individual Decision Influence for Proposal Admission in Decentralized Federated Graph-Level Clustering

Decentralized federated graph-level clustering must admit peer proposals while preserving a shared clustering state. Updates that appear ordinary in parameter space can change assignments near small decision margins, so nominal authority need not reflect decision influence. To audit these effects while preserving execution continuity, we introduce Proof-Carrying Operator Consensus (PCOC). Peers commit aligned operator and claim pairs before an unlabeled audit challenge is sampled. Validators measure each proposal's leave-one-out effect and compute simultaneous upper bounds for individual influence in the frozen audit pool. The policy screens proposals using current and stored upper scores, then ranks passing proposals to select a fresh quorum. Stored pairs fill the remaining positions. Across five datasets with matched budgets, mean individual influence was 45.8% and 45.6% lower than for an internal reference under fixed and adaptive attacks. In a separate study with two encoders and 20 paired seeds, attack-induced boundary-flip rates (AI-BFR) were 6.3% and 5.2% lower, corresponding to approximately 0.052 and 0.047 percentage points. Neither difference passed Holm adjustment, with $p$ values of 0.0625 in both attacks. Final clean normalized mutual information (NMI) was 0.1199 versus 0.1217. A transfer record covering 50 contexts found lower influence in the execution pool for PCOC in 43 of 50 contexts.