Public HIV-1 drug-resistance surveillance derives per-drug Sierra levels from pol sequences without observed individual treatment history. Naive associations between mutation features and Sierra levels conflate causal drug pressure with subtype-specific polymorphism and non-random sampling. CausalPhylo v1 specifies a DAG-based identification framework and validates it on synthetic ground truth. This preregistration locks the real-data application against SAWA v0.1.0 in advance of running the analysis.