Yep. Anybody who wears a well-fitting N95 wherever they go is in a rather safe place.
Breakthrough infections are still technically possible, but quite unlikely.
Most covid19 infections are asymptomatic so unless you treat every day you can't know;)
Well, even the antibody titre isn't foolproof (some people do not react or have their immune system later wiped).
However having no antibody titre is pretty good sign you never had it.
Not sure if there's a portable cheap blood test for it yet. Should be one, like for the active disease.