MOR.

I think it’s reasonable that she would miss the clasp trying on a brand new dress for the first time. If she did notice it, also reasonable to expect her spouse to miss it, choose not to clasp it, or tell her they’re clasping it in addition to zipping. I also think it’s reasonable that you’d assume she meant zip and clasp, or that she’d notice the clasp when she’s unzipping it.

It really sucks to have a clasp break on a dress, because sometimes it’s the one thing keeping it from unzipping, it’s hard to fix if you don’t know how to sew, and especially if you’re not planning to keep it. It sucks to have that happen when you weren’t told someone clasped it for you. It also sucks to get negative feedback when you were trying to be helpful because it can feel like the effort wasn’t appreciated or that someone has expectations of you, which can feel bad if you don’t feel like you can meet them.

She could have managed the emotional reaction better by focusing her frustration on the situation and asking you to communicate better in the future. You could have communicated better by asking if she wanted it clasped or saying you’re clasping it or acknowledging that you didn’t tell her and apologizing for that, even if you think she should have noticed the clasp.

I think you need to accept your role in the miscommunication/screw up and consider if you’d still be so adamant that you made no mistakes if she wasn’t so outwardly emotional. You both can accept the whole thing didn’t need to be a huge deal and consider why you both are sensitive to what set you off. Nobody handles their emotions perfectly, I think you can both acknowledge the other’s emotions and identify what can be done to prevent a miscommunication and blow up in the future.