Since it's printing something out I suppose it also has everything else virtualised, would be cool to be able to provide it some machine code / assembly
You can interact with it using a wasm-based assembler in your browser. Programs only get 100 cycles to run but that should be plenty if you just want to poke around.
See also https://www.righto.com/2012/12/the-6502-overflow-flag-explai...
I also note that you have the same code copy/pasted in every ALU operation which might be better expressed in one location for maintenance reasons.