Syscall.CallAsync struggles with large stdins

Specifically on Linux, if I send more than 4097 bytes to stdin I get ch_sendraw(): write failed
If the command produces output, then vim hangs indefinitely, before even displaying the ch_sendraw error.

This looks suspiciously like https://github.com/vim/vim/issues/2548

Tried to patch it with https://github.com/natebosch/vim-lsc/issues/67#issuecomment-357469091

but I don't actually know what I'm doing in vimscript and just ended up with some channel closed errors after the first chunk. Also I could be barking up the wrong tree.

For me personally, I'm no longer using stdin so I'm no longer affected by this but still seems like a bug?