What protection did the Concorde have against an uncontrolled decompression?
This is the main reason why Concorde had such small windows. It was calculated to reduce the rate of decompression to a survivable level in case one window fails. (The prototype, by the way, had much larger windows).

Other than that, I don't know of any other 'special' decompression mitigation measures that would be unique to Concorde.

There were, of course, things that had to be done in a very special manner on Concorde in case of decompression. For example, rapid emergency descent: there was a special program that transfered fuel forward during emergency descent. It could be activated by a single button, and the flight engineer had to keep the program up to date for the current flight conditions. (Generally, keeping the CG/fuel balance was pretty much a full time job for the Concorde flight engineer). But this would hardly help in case of 'uncontrolled' (explosive) decompression.