> Are these limitations listed in some document?

I don't believe they are.

It might bve nice to think there are no arbitary limits in plan9
as the GNU mantra, however there are not many and personally,
working with remote servers with very long paths, I have never
(knowingly) hit this limit.

Having said this we could probably afford to up the size of pwd's
buffer to, say, 8k to be sixteen times as sure.