Solved
What is the part-shrouded STDC14 connector used on STLink/V3 Mini?
On STLink-V3MINI (https://www.st.com/resource/en/data_brief/stlink-v3mini.pdf) there is a neat connector used for the STDC14 connection, which has the top and bottom sides of a box header but no ends. This means it takes up a smaller footprint space than if it was a normal box header, but is still keyed (unlike just using a pin header with no plastic sides).
Can anyone tell me where to find a connector like this, for my own boards?