If areas are marked with an Out of Supply marker (rule 15.4.1) how do Out of Supply units work? It seems that units are not marked Out of Supply.
Is it correct to say that any unit that enters an Out of Supply area is immediately Out of Supply, and conversely, a unit that moves away from an Out of Supply area to a supplied area is immediately in supply?
If the preceding is correct, how would movement points work? Would a unit immediately regain the -1 movement point if it moved from an Out of Supply area to an supplied area?
First rule of thumb: never allow yourself to be put OOS.
Second rule of thumb: units that get put OOS rarely do anything other than get eliminated. A good opponent is going to jump on them like a shark sensing blood in the water. You're not going to reestablish contact.
Having said that the rule is quite explicit: the marker is in an area. Area effects. In the area, effects apply. Not in the area, effects do not apply. How long do they apply? The whole impulse the unit is activated, not part of it.