My Guess . as said above a stopper hole at the ends of the crack.

Maybe someone can TiG weld the crack, then ream out the distortion of the seat tube to get a seat post back in.

The Brazing a Patch is Good too , as Long as the filler wire used to make the original TIG weld was Not Stainless

Stainless wire is popular to use , but brass wont stick like it will with plain steel filler wire , then

the use of silver content solders will be better , but they flow thinner and so you need the patch to fit more precisely.