I think secure attachment doesn't just happen, it's rather that first you attach in whatever way you're used to and then you talk about the way you attach. As Echos said, if the T is consistent, with time you learn that you can attach in a different way, that you can feel safe in this relationship. And from that you can hopefully learn that it can be this way with other people too. I'm not sure understanding attachment and being safely attached has much to do with working through trauma. Attachment and trauma can be connected, but it doesn't have to be. But being safely attached certainly helps with therapy in general. But that doesn't mean you can't do work when you are not safely attached, it's just one topic that should probably be talked about.

I can talk to my T about whatever issues I have regarding attachment, he will listen, understand and try to show me where my issues come from. For example I struggle with being scared that he might get mad at me or just suddenly stop talking to me a lot. He might tell me that I'm projecting that onto him, and that this might come from situation X that I experienced previously.
I think in general it helps me to know that I can count on my T, that he has so far never failed at being the T I need. He also occasionaly reassures me that my fears are just in my head and his experience is very different to what I might think.

As for ruptures, usually I get upset during a session by something he says, and I will go back the next time telling him I'm angry/disappointed/whatever else I feel about what he said. We will talk through what happened exactly, then why it upset me (if it's not obvious). If it's a mistake on his part, he will apologize and explain his thinking. If it's more something that I'm just making worse than it was, he won't apologize, but he will still explain why he did what he did. We might also discuss what we could have done differently and how we can manage that it doesn't happen again. Then, he'll always empathize that he thinks it's good that we talked about this, ask me whether I'm satisfied with everything we discussed or whether there's something else that needs to be adressed regarding it.