EXCLUSIVE : Here’s a big one. Will Smith has just committed to star in David Gordon Green-directed action-thriller Supermax , about two FBI agents investigating a murder that’s taken place in the world’s most secure prison.  In a deal pegged in the $70M range, Amazon MGM Studios has this week closed a pact for worldwide rights to the Miramax project, which will mark Smith’s first non-franchise studio movie in recent years. We understand this one will be a streaming play and not a theatrical release. Additional casting is underway — Smith’s FBI agent partner is a female part — with production set to begin mid-August. Pic is written by David Weil and David J. Rosen, known for their work on the TV series Hunters and Invasion . The Picture Company partners Andrew Rona and Alex Heineman are producing. Will Smith and Adam Fishbach will produce for Smith’s Westbrook. CAA Media Finance brokered the deal.…