Ex's 6th sense — they must KNOW you're doing NC

Okay, so a quick question. You can read my other post about the situation.

Anyway, I had been debating reaching out to the ex after the 3rd day of an unexpected break-up. Then I came across the No Contact strategy. So JUST as I’m ready to employ this strategy (yesterday) and feeling good about it, my ex reached out in two ways. Now I don’t know what to do.

1. We had used a To-Do List app for our phones that we shared. Put fun things to do on there and wrote some little messages or “assigned” them to each other. We don’t get notifications when someone does it. I randomly checked it yesterday and saw that she was still on the shared list and had added something:

“Tell Nick that you’re sorry and that you miss him and that you hope he’s well”

Like I said, there is no way that she knows I saw that. And that list represented us being cute and nice.

2. Later that night, around 9pm when she knew I was leaving work, she texted me:

“Hey you. I know this text will never be good enough, but I am so sorry for any hurt I caused. I miss you and I hope you’re well. Goodnight, Nick”

Do I respond? This sounds like a breadcrumb to me. But I don’t know the rules. Do I respond politely and shortly because I’ve always been nice and kind to her. Do I say, “I’m sorry too. I hope you’re doing well.”
Or “Thanks for letting me know. I hope you’re doing well.”
Or “I hope you’re doing well, too.”
OR something else?!

I don’t know if I’m supposed to just ignore. What if it makes her upset or pushes her away? She can be stubborn. I don’t know if she is reaching out and trying to start the steps to reaching out again and talking.

Advice?