In this setting, Humans have done multiple advances in technology and are nearly on the verge of being a Type III civilisation, They have nearly colonized the Milky Way and have tapped energy from nearly all the energy sources available. They are now in war with a rival alien civilisation. The two sides are on a stalemate. Until a human engineer comes up with a plan.
The idea is to take a massive star, around 10-20 solar masses, and make a reflective shell that completely surrounds it. The shell does not have to be completely thick, it is just as wide as aluminium foil. Thus, as the star emits light, this light is again reflected back by the shell onto the star, which heats it up a bit. The star then glows more brighter due to the heat, as it fuses hydrogen more quickly, and emits more light, which is reflected back and heats it up again. This results in a runaway-reaction that causes the star to explode, either from it ridiculously getting crushed by its own radiation pressure and rebounding back, or by the intense heat produced. The radiation and heat released would incinerate nearly anything within the vicinity.
This weapon is used to maximise heat/radiation damage to the enemy, and wipe out their army.
What are the drawbacks of this design, and if any, what should I do to fix it?