Perspectival White Holes: A Priority Note on White-Hole Causal Roles in Collapse Spacetimes

White holes are conventionally represented as time-reversed black holes: spacetime regions from which matter and signals may emerge but which cannot be entered from the exterior. In the maximal analytic extension of the Schwarzschild solution, this role belongs to Region IV, bounded by a past horizon and a past singularity. Region IV is absent, however, from ordinary black holes formed by collapse at a finite time. White holes treated as independent external astronomical objects also face well-known problems of formation, thermodynamic interpretation, instability, and non-observation. This note proposes a different referent for white-hole terminology in realistic collapse spacetimes. A perspectival white hole is an observer-relative causal structure arising after a timelike observer crosses a future black-hole event horizon. Parts of the exterior universe can remain in the observer's causal past and continue to send signals inward, while the exterior is no longer available as a future destination. Relative to that worldline, the exterior is therefore presented as a horizon-mediated source without future return. The proposal does not identify the black-hole interior with Kruskal Region IV, introduce a new solution of Einstein's equations, or claim that an external white-hole object has been observed. It is a re-referencing proposal: the physically available carrier of a white-hole causal role in finite-collapse spacetimes may be relational and horizon-based rather than a separate past-trapped region or astronomical body.