CompulsionBench: A Benchmark for Auditing Compulsion-Risk Proxies in Sequential Recommendation

We introduce CompulsionBench, a reproducible benchmark for auditing and mitigating compulsion-risk proxies in sequential recommendation under explicit, non-clinical assumptions. CompulsionBench asks when engagement-oriented policies interact with long-horizon user dynamics to increase observable behavioral proxies, including prolonged sessions, late-night session starts, rapid-return diagnostics, and watch time accumulated beyond a fixed session threshold. It also asks which mitigation strategies reduce those proxies under matched evaluation. CompulsionBench combines a partially observed user simulator, tunable platform controls for personalization and reward variability, mitigation interventions including session caps and observable-risk constrained optimization, a public-log calibration and feasibility-audit protocol, and a standardized scorecard that separates observable compulsion-risk proxies from latent mechanism diagnostics. The released benchmark provides two plug-compatible user-response backends: a transparent parametric simulator used as the reference environment, and an LLM-augmented semantic robustness backend that preserves the same observation space, action space, interventions, calibration targets, and scorecard while perturbing the item-response kernel under the same benchmark interface. CompulsionBench defines two benchmark tasks, engagement maximization and observable-risk constrained optimization, and reports tail-risk and mitigation metrics for every policy. In the released active-threshold profile, high-watch deterministic heuristics produce higher over-cap exposure than PPO, while a simple session cap reduces PPO over-cap exposure from $2.84$ to $0.45$ minutes at a $4.1$ watch-time cost. Episode-level diagnostics further show that the cap is a tail-severity intervention: over-cap incidence is essentially unchanged, but deterministic p95 over-cap exposure falls from $14.23$ to $2.36$ minutes without a short-gap re-entry spike. A reference 120-minute profile shows that the same over-cap channel can be inactive, highlighting the need to report threshold provenance and proxy activation. CompulsionBench makes audits of compulsion-risk proxies and mitigation strategies reproducible while remaining explicit about construct-validity limits.