Social bot detection on emerging platforms is constrained by sparse labels and by evaluation practices that focus on classification accuracy while ignoring network validity for network analytics. This study proposes a graph-based semi-supervised bot detection framework for Bluesky. From 2.2 million accounts, we construct 6,891 high-confidence bot seeds and 683,209 conservative non-bot anchors without treating unlabeled accounts as humans. We then introduce a Role-Discrepancy GNN that models directional role asymmetry across repost, reply, quote, and mention relations. On a temporal test split, the proposed model achieves the best overall performance among profile-only and graph-based baselines, with AUC = 0.9930 and F1 = 0.8936. Network validation further shows the strongest structural separation, with modularity Q = 0.0547 and mean homophily gap ΔH = 0.0515. These results support relation-role discrepancy as a useful signal for bot detection under sparse labels.
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Abstract Introduction Related Works Social Network Analysis Social Bots Social Bot Detection Graph-based Bot Detection Models Methods Research Design Data Proposed Model Evaluation Results Classification Network Separation Conclusions Discussions Limitations Future Works Acknowledgments References