You suppose that there are no highly-paid researchers on the planet working on AGI? Because there are, and that's less proven than "porting one codebase to another language" is. What about Quantum Computers, what about power-producing nuclear fusion? Both less proven than porting code. What about all other blue-sky research labs?

Why would you continue supposing such a thing when both the employee, and the employer, have said that your suppositions are wrong?

Sure, there are plenty of researchers working on fanciful daydreams. They pursue those goals at behest of their employer. You attempted to make a distinction between the employer and the employee's goals, as though a Distinguished Engineer at Microsoft was just playing around on a whim doing hobby projects for fun. If Microsoft is paying him $1m annually to work on this, plus giving him a team to pursue the goal of rewriting Windows, it is not inaccurate to state that Microsoft's goal is to completely rewrite Windows with LLMs, and they will earn negative publicity for making that fact public. The project will likely fail given how ridiculous it is, but it is still a goal they are funding.