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Identify the mechanism (wave energy transport from core convection in the last burning stages, binary interaction, pulsation-driven winds) and whether it also produces observed pre-explosion outbursts. Answer: a mechanism predicting circumstellar mass and extent versus progenitor mass and evolutionary stage.","problem_ref":null,"references":"","settled_by":"Pre-explosion monitoring of many nearby supernova progenitors combined with early spectra, compared with predicted outburst timing and circumstellar masses.","status_note":"2023: SN 2023ixf in M101, the nearest Type II supernova in a decade, showed dense, confined circumstellar material.","title":"What drives heavy mass loss in the final years before 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