OP I have a similar issue with ds. Teacher was in a hurry and just wanted ds in asap, she just grabbed his arm and pulled him inside the classroom with a sharp 'sit down now' (We weren't late btw but yes ds did struggle to go into the class. I'm wondering why
).
That day they did an assembly with parents and ds went on the stage looking miserable and didn't open his mouth the whole time. At the end of it, we had the opportunity to come and 'congratulate' the dcs so I went to give ds a cuddle and it took him a good 5~10mins to relax again. I swore that I would never let that to happen again!
Unfortunately, in my case, this was a sign of a more general attitude in the school and I ended up changing school.
What I learnt is that you will be better sending an email/letter to HT before and after the meeting. The first one to set the problem out, the second to establish and have in writing what has been agreed.
I wouldn't propose any solutions in your letter, nor would I give the HT some ammunitions re your ds behaviour (he has separation anxiety issues due to frequent trips to hospital, therefore it's 'his' fault, not the teacher). I would state very clearly what has happened (your ds screaming for a good bye kiss that he didn't had, him being taken away from you by force) and state just as clearly the guidelines for FY re dealing with children. I'm sure that taking the child from the parents by force isn't in them!
Say that you want to have a chat regarding this unacceptable behaviour and that you want to find a way to support the teacher and your ds to settle in a way that is appropriate for your ds.
Explain that you actually had thought about some way to help him (the bracelet) but that, unfortunately, you didn't get the opportunity to talk to the teacher about it.
Take some notes during the meeting. Don't let the HT railroad you into doing something you don't want. Then when you've had the meeting with the HT (I would expect the teacher to be present too tbh), send an email again detailing the agreement.
With a bit of luck, your HT will be easier to handle than mine who thought that being aggressive was the best defence strategy. She also looked shocked when I took a pen and paper to take notes. 'But you are not going to write what I'm saying!' Err actually yes. That's what you do in meetings.'