ResentMessage stacks duplicate `resent` tags when resending a resend

[jszobody]

This issue was written by Claude (Opus 4.8).

Symptom

Resending an already-resent message produces duplicate resent tags. A first resend gets […original tags…, resent]; resending that copies its tags and appends resent again → […, resent, resent]. Each further resend adds another, so the badge row grows resent resent resent ….

Cause

STS\Postmaster\Mail\ResentMessage::build() (around line 67):

foreach ((array) $this->record->tags as $tag) {
    $this->tag($tag);
}

return $this->tag('resent');

It copies every tag from the source record — which already includes resent when the source was itself a resend — then unconditionally adds resent again.

Suggested fix

Don't re-add resent if it's already carried over (and, defensively, dedupe the copied tags):

foreach (array_unique((array) $this->record->tags) as $tag) {
    $this->tag($tag);
}

if (! in_array('resent', (array) $this->record->tags, true)) {
    $this->tag('resent');
}

return $this;

The resent tag is a boolean-style marker ("this send is a resend"); resend depth is already tracked precisely by the resent_from_id chain (resendChain()), so a single resent tag is all that's meaningful.

Workaround in the meantime

Consuming app dedupes on display (array_unique($message->tags)), but the stored tags column still accumulates, so the fix is best at the write side.

Happy to PR.