This incident, this quote:
How would I go about this? They told me repeatedly that I was not arrested, but that I wasn't free to go. What should I do? I would certainly like legal recourse toward the officers involved if any is possible, even if they're just told "DON'T DO THAT AGAIN!"
If you were handcuffed, you were effectively detained for suspicion of lawful activity. The police acknowledge that you didn't break any laws. You were standing in a checkout line when they walked in, so there was nothing to give rise to a "reasonable suspicion based on clearly articulable facts" (Terry stop language) that a crime was being committed or was about to be committed. Therefore, legally they didn't really have any right to lay a finger on you. In fact, since the incident didn't meet the criteria for a Terry stop or a Terry frisk, they had no right to disarm you even if it was for their safety. You really REALLY should sue them for false imprisonment.
How would I go about this? They told me repeatedly that I was not arrested, but that I wasn't free to go. What should I do? I would certainly like legal recourse toward the officers involved if any is possible, even if they're just told "DON'T DO THAT AGAIN!"