Re: This is unnecessary
I'd have made a written and signed statement about the incident and handed that to the junior. Plus told him that if they end up in court over that new contract I witnessed the exchange and am willing to testify against the boss. (And advise him to go to a lawyer about having the boss/company tear up the new contract with threats of legal action about coercion). Mention the L word and many many companies suddenly reconsider their hardline stance.