Pkg fails to print all output from subprocesses

[vtjnash]

It seems there is some mistake in Pkg IO handling that results in it truncating the output from subprocesses. A possible reason is the mistaken use of IOBuffer, when that is supposed to be forbidden to use for stdout. One example is at

Pkg.jl/test/utils.jl

Line 303 in c3b9d3e

out = IOBuffer()

I have been too busy and forgot to implement the error when I added automatic conversion functionality (for stdin and BufferStream), but this may lead to problems with corrupt output. I think the upstream issue for this is
JuliaLang/julia#46768 (comment)

[IanButterworth]

when that is supposed to be forbidden to use for stdout

AFAICT the documentation of this is that it's explicitly not in the list in the note here https://docs.julialang.org/en/v1.10-dev/base/io-network/#Base.redirect_stdout

Would it be possible to improve the docs. Perhaps a short section on buffering best practices linked to in all relevant buffer types and redirect functions?

[vtjnash]

A second mistake is that someone called closed(iob), which prematurely truncates the stream and creates many problems.

[IanButterworth]

Fixed by #3573