30-year cycle spring failure
If your torsion spring, rollers, and cable drum are original to the house, they're closing in on thirty years of cycles - and that's the point where a spring doesn't announce it's tired before it snaps. The usual failure pattern on a door this old: rollers that have gone from nylon-smooth to grooved and loud, a bottom bracket with hairline rust from three decades of humidity swings, and an opener drive gear worn thin from carrying a spring that's lost tension without anyone noticing.
