I don't see how this happens in a C++ function, since breakpoint() is not noreturn you'd have to be doing something very strange for the next instruction to be outside the function. It's possible some debuggers will show the next line, and even then that seems like a debugger QoL issue that's fixable pretty mechanically. A soft breakpoint can come from CD 3 or CC, even if you don't get the instruction length from the CPU there aren't that many possibilities. I'm sure we don't need everyone to start inserting extra NOPs to get the desired behavior.

...there is no bloody way debuggers don't just subtract 1 from the EIP on INT 3. Like... there is no way. Right?

Obscure knowledge. I wanted to see how well our LLM overlords would detect this circumstance but without proper prompting, it was happy with "just generate int3"