Invariant Hyperbolic Unfolding: Radial Canonicalization for Label-Free Cross-Graph Link Prediction

We study label-free, topology-conditioned zero-shot cross-graph link prediction: at test time the observed target topology is the input graph, but the model receives no target labels, no positive/negative context links, no target fine-tuning, no text attributes, and no post-hoc alignment. This setting is zero-shot with respect to target supervision and adaptation, but it is not topology-free inference. We identify a critical geometric barrier for hyperbolic transfer: radial non-identifiability. Hyperbolic graph learning is motivated by the intuition that radius encodes hierarchy or popularity and angle encodes similarity, yet standard HGNN objectives do not make radii semantically calibrated across disjoint graphs. The same structural role can therefore occupy incompatible radial scales on different target graphs. We propose Invariant Hyperbolic Unfolding (IHU), which restores the intended radial hierarchy channel through selective invariance: radii are fixed by graph-internal structural percentiles while angular representations remain learnable. Its core module, Invariant Structural Anchoring (ISA), rank-canonicalizes structural scores such as coreness into shared hyperbolic radii, producing a comparable radial skeleton without target supervision. In a controlled comparison among matched frozen learned encoders, IHU improves average HR@50 by 2.7 percentage points over the strongest learned hyperbolic baseline and by 7.6 percentage points over the mean of the learned hyperbolic baseline family. The gain amplifies under missing-edge and low-degree regimes, while hierarchy-gap analysis reveals a boundary condition for fixed radial shells: 50% edge sparsification causes 52.5% less degradation, and low-degree nodes show a 4.2× larger advantage. We further position IHU against recent universal link prediction and graph foundation methods through an access-aware taxonomy, showing that the closest recent LP methods use labeled target context links, whereas IHU isolates the geometric effect of fixed versus learned radii in frozen structural hyperbolic encoders.