I think your read loop in the Messaging class is a little too greedy:

ABORT:while(<$fh>){
        my $data = $_;
        my $params = fd_retrieve($fh);
        ...
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This first reads a line, then does an fd_retrieve(). Your test script first does an nstore_fd(), then writes some text, i.e. exactly the other way around.

This is not the only problem with your code. Apart from style/idiom issues, the fact that you are mixing plain text with binary text in the same channel is asking for trouble. If you reverse the writing order in your test script, the fact that the text string in our test script does not contain a newline will most likely trip up the <$fh> statement and slurp up the nstore-d data as well. (And if you have a string with more than one newline you also have a problem.) You should really consider using some appropriate encapsulation, like a hash with both the data and the parameters, written out with nstore:

  # Writing a message:
  my $message = {
    data => "Some message\nthat can contain newlines\n",
    params => \%params,
  };
  nstore_fd($message, $fh);

  # Reading a message:
  my $message = fd_retrieve($fh);
  my $params = $message->{'params'};
  my $data = $message->{'data'};
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... Or something like that.

Hope this helps!

-- Steven