An Application Note: Registrability-Based Structural Classification of the ASSASSN-24fw Dimming Event

Long-duration stellar dimming and apparent disappearance events frequently prompt interpretive escalation toward rapid stellar evolution, envelope collapse, or imminent supernova. In many cases, these narratives arise from conflation of changes in observational registrability with changes in stellar structure. This application note applies a registrability-based structural classification framework to the long-duration dimming event ASSASSN-24fw. The framework enforces ordered constraint tests—duration scaling, chromatic behavior, multi-channel response, geometric admissibility, stability bounds, recurrence, and identity preservation—prior to any evolutionary inference. Evaluation of the published observational record shows that ASSASSN-24fw is structurally consistent with a stable, identity-preserving occultation system. Near-achromatic dimming, symmetry of ingress and egress, recurrence, infrared response, polarization, and full spectral recovery collectively exclude terminal registrability collapse and intrinsic stellar transformation. This case study demonstrates the utility of registrability-based classification as a disciplined first-pass diagnostic for apparent stellar disappearance events and provides a reusable template for future survey-driven anomalies. Terminal collapse phenomena, including supernovae, are explicitly excluded from the present analysis.