The gate agent was indeed summoned; she was too busy to come by herself because she was closing the flight (ARGH), but she called the gate manager. Everyone (the gate agent, the gate manager, the people who load luggages -- gate workers? -- onto the plane) was confused; the gate workers even asked the flight attendant whether there was anything they can do to let me back on the flight, and he simply said no. He refused to give me any suggestions on what I could do to either get myself back on that flight, or retrieve my belongings (including my wallet and my laptop) on the flight.

I did call the airline, and the person answering the phone, as well as her supervisor, seemed confused about what the correct protocol was supposed to be.

Thank you for your help everyone. I'm going to poke around some possibilities this weekend, talking to other frequent travelers and maybe trying to find some legal personnel or two to get some advice. Maybe it's not worth anything, but at the same time, does the law really not protect you when you were scared for your personal safety? I suppose that I'm quite upset at the moment, but I'm hoping that a weekend of mulling this over will come to some conclusion.