The paper states a pragmatic retrieval objective: improve recall of gold prerequisite chains while keeping retrieved contexts interpretable and reproducible. Recall of gold chains is the optimization target (so missing a true prerequisite is the failure mode that matters), and the interpretability + reproducibility constraint motivates deterministic, auditable graph policies and fixed-interface comparisons rather than opaque end-to-end retrievers. This objective is what justifies the paper's later choice of deterministic diffusion and strict-parity headline reporting.