What is the primary factor determining the pathway a star takes toward a supernova ending?

Answer

Its initial mass.

The text explicitly states that the fate of a star, including whether it ends as a core-collapse event or influences a white dwarf, is fundamentally dictated by the mass it possessed when it first formed.

What is the primary factor determining the pathway a star takes toward a supernova ending?
astronomystellar evolutionsupernovastar deathviolent