Update:

I found version 20000216 of Win32::Pipe on roth.net, installed that, and now I'm able to do a vanilla perl file open, but it passes me the same sort of garbage the Win32API::File version was.

I am trying to interpret this as good news for me, but I haven't succeeded yet...

#  Vanilla file implementation

open( PIPE, "+<" . $PIPE_NAME )
    || die "couldn't open pipe";

print PIPE "vanilla!\0";

my $result = <PIPE>;
print "Server said [$result]\n";

foreach (split //, $result) {
    print  "[" . (ord $_) . "]";
}
print "\n";

close PIPE;
[download]

Output of the two look like:

Server read: [vanilla! { require $path; };
]
[118][97][110][105][108][108][97][33][0][123]
[32][114][101][113][117][105][114][101][32][36]
[112][97][116][104][59][32][125][59][13][13][10]

and...

Server said [{ require $path; };
]
[123][32][114][101][113][117][105][114][101]
[32][36][112][97][116][104][59][32][125][59][13][10]
[download]

(line breaks within the ord dumps inserted for clarity)

Perhaps I'd just fumbled the open call, earlier, when I couldn't get the vanilla file version working.

Clearly, though, I'm getting too many characters. The \0 at the end of my client send was pure desperation--sending a \n doesn't stop it correctly either.