turns out CPU JIT was the issue, which i 100% should have foreseen. it makes a lot of breakpoints unreliable, obviously, and now that it's off (thanks LITERALLY THE PABLOMK7 for the help) it works pretty well!
however, he seemed pretty skeptical that the memory addresses past the base of the stack at 0x1000000 were the heap, which means either tomodachi life is special or i'm just reading garbage memory that the gdb stub somehow lets me access. either way, that's less important than the fact that we're making progress!!
i was able to find this function that accesses the filenames of the .msbt files!! it looks like it loads everything at the start..? twice? which really confused me. this function isn't called again and the memory isn't accessed at all after the game loads