For me safety and containment takes a bit of time. But I think for me with this T, I had a strong sense from the beginning that she was good at her job, she was knowledgeable and experienced and kind. I also questioned her extensively at the interview stage about her perspective on certain situations, how she would handle A,B,C scenarios. So I knew her ethos, what I could expect from her.
As the months went on, I tested her a fair bit and she passed pretty much every time. She contained things be being trustworthy, predictable, flexible but with boundaries. She is interested in all my feeling and emotions and behaviours and welcomes them all, even the difficult ones.