I'd guess the prompts and employees. I've found Windsurf more reliable/efficient than any other editors by leagues. How ever they have named the tools, crafted

I'd guess the prompts and employees. I've found Windsurf more reliable/efficient than any other editors by leagues. How ever they have named the tools, crafted their prompts and generally how their internals reason is just on the money. I don't think that is easy to replicate, iterating on prompts over product releases whilst not pissing off your user base constantly is a feat in of itself.