ExtractSubjectTag Action: prepend, not append, remote system's subject tag

[Al2Klimov]

Too long (200+) ticket subjects (produced by this action) are shortened automatically.
This could cut off the remote system's subject tag if at the end.

[Al2Klimov]

How to reproduce

1. Setup two RTs, say, Tom and Jerry
2. In Tom create a ticket with a loooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooong subject, add Jerry as requestor and reply something
3. In Jerry reply to the ticket
4. In Tom reply to the ticket -> opens separate ticket at Jerry

[Al2Klimov]

Why exactly this happens

To understand the following we need to remember that there are ticket subjects and eMail subjects.

1. In Tom the newly created ticket has the ID 1 and the ticket subject looooooo... (cut off).
2. On "reply" (it's not actually a reply, but the very first message of the whole conversation) Tom sends an eMail to Jerry with the eMail subject [%s #%d] %s, i.e. [tom #1] looooooo... (cut off).
3. That eMail creates a new ticket in Jerry with ID 1 and the eMail subject from above as ticket subject.
4. On (actual) reply Jerry sends an eMail to Tom with the eMail subject [%s #%d] %s, i.e. [jerry #1] [tom #1] looooooo... (cut off).
5. Tom recognises [tom #1] in the eMail subject and associates the eMail with the existing ticket.
6. Tom also recognises the foreign tag [jerry #1] and the code I changed in this PR tries(!) to change the ticket subject to loooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooong [jerry #1] (so that on next reply from Tom gets into the right ticket at Jerry). It tries! But, as master Yoda said: Do or do not. There's no try. Effectively Tom doesn’t change the ticket subject as above as [jerry #1] gets cut off silently due to the database column length.
7. As the ticket subject stays as-is the next reply from Tom misses [jerry #1].
8. Therefore Jerry can’t associate it with the already existing ticket and creates a new one.

[Al2Klimov]

How to workaround

At least in the Tom RT, preferably in both ones:

1. Navigate to Admin/Scrips/Select
2. Open On transaction, add any tags in the transaction's subject to the ticket's subject
3. Set Action to User Defined
4. Set Custom action preparation code to 1;
5. Copy the code given below to Custom action commit code
6. Apply this PR as patch
7. Save Changes

rt/lib/RT/Action/ExtractSubjectTag.pm

Lines 103 to 131 in cbfe3cd

	my $Transaction = $self->TransactionObj;
	my $FirstAttachment = $Transaction->Attachments->First;
	return 1 unless $FirstAttachment;
	my $TransactionSubject = $FirstAttachment->Subject;
	return 1 unless $TransactionSubject;
	my $Ticket = $self->TicketObj;
	my $TicketSubject = $self->TicketObj->Subject;
	my $origTicketSubject = $TicketSubject;
	my $match = RT->Config->Get('ExtractSubjectTagMatch');
	my $nomatch = RT->Config->Get('ExtractSubjectTagNoMatch');
	TAGLIST: while ( $TransactionSubject =~ /($match)/g ) {
	my $tag = $1;
	next if $tag =~ /$nomatch/;
	foreach my $subject_tag ( RT->System->SubjectTag ) {
	if ($tag =~ m{\[(?:https?://)?\Q$subject_tag\E\s+#(\d+)\s*\]}) {
	next TAGLIST;
	}
	}
	$TicketSubject .= " $tag" unless ( $TicketSubject =~ /\Q$tag\E/ );
	}
	$self->TicketObj->SetSubject($TicketSubject)
	if ( $TicketSubject ne $origTicketSubject );
	return (1);

CC @lippserd