Same client-side principle I use for a colour-by-letter PDF generator. Browser-only really is the right answer for these single-use file tools. Curious what you're using for the PDF assembly, pdf-lib or something else?

Can it be used easily for streaming things other than AI tokens? Long-running progress updates, log tails, SSE for webhook fanout, the OpenSwoole base seems like it should support these but curious how friction-free that is in practice.

Yes.. for all! Its a PHP application server! We created a custom C extension to solve all long running caveats, including session support, superglobal support! Its friction free, and coroutines safe!