Your assumption being that Oswald exited the TSBD via the front door. Nobody knows with certainty exactly how Oswald exited the TSBD. Buell Frazier has now claimed that he saw Oswald walking alongside the TSBD on Houston St. This positioning of Oswald would indicate that he probably exited the TSBD via the Houston St Dock. This is the same Dock that Oswald and Frazier used to enter the TSBD when they reported for work that morning.
The TSBD building, the area immediately around it, and Dealey Plaza on the whole, have been altered in many, many ways over the years. The TSBD and the area surrounding it does NOT come close to appearing as it did on 11/22/63. The TSBD Houston St Dock is completely GONE. If you go to Dealey Plaza to survey the 11/22/63 JFK murder scene, bear in mind that you are NOT seeing anything close to the actual murder scene. Arriving at any conclusion(s) based on what you see there today is a journey down a rabbit hole. You MUST do serious research in order to Know how Dealey Plaza, the TSBD, and the area around the TSBD looked on 11/22/63.