> While I'm sure [bumping the stack pointer atomically] makes sense, I don't think I've ever seen that be enforced. At least in C/C++.

That’s because the C ABI supports unwinding with a fairly expressive set of tools for describing stack-pointer state on a per-instruction level. Even the simpler Microsoft ABI essentially uses bytecode for that[1]; and on the more complicated Itanium ABI, you get DWARF CFI instructions, which make the correct way to preserve a(n x86) register in the function prologue look like

  push rbx
  .cfi_adjust_cfa_offset 8
  .cfi_rel_offset rbx, 8

which are impossible to miss when reading compiler-generated assembly because of the sheer amount of annoying noise they create.

The Go authors decided to sidestep all of this complexity, which is understandable to a degree, but apparently they did not think through all the ramifications of doing so.

[1] https://learn.microsoft.com/en-us/cpp/build/exception-handli...