I've seen the Bun Zig->Rust MR a few weeks ago when it was current. Now I'm seeing this, and I have to ask, since you're here:

Is there no way to make this changeset smaller?

At work, I've usually written large patches. I used to be worse at it. I was mentored out of it, and while I still like my patches to be complete, I balance that with the available bandwidth of the team and what the team can reasonably actually process.

For perspective, my "large patches" were PRs on the order of 10-12kLOC for relatively big features. I consider those to be on the upper end of what is reasonably reviewable by a small, non-dedicated team, and towards the upper limit of the kind of PR where I can speak for nearly every line of code, what it does, and why it's there.

On the other hand, now, LLMs are part of the equation, and they can (and often do) write code in insane volumes. They arguably tend towards extreme verbosity, without even talking about docs/markdown files. While LLMs are part of the workflow, my company, and those my friends work at, have all instituted policies of the developer attaching their name to the code ultimately being responsible for the output (which IMO is a lazy strategy, but I can't think of a much better one under the circumstances).

I cannot, personally, fathom how you can stand behind a single changeset spanning 2000 files and a quarter-million lines of diff. Do you consider this sustainable?

At this point the code bases are very quickly getting away from us in the open source community and even in proprietary code bases, and these are important code bases. Often very complex, often legacy. Who ultimately still owns these? Who's really going to be accountable if things go wrong?