Microsoft’s stock has fallen to a price level where buyers have repeatedly stepped in, but this time it arrives with an unprecedented spending plan that will define the battle.

Microsoft (MSFT) stock is back in a familiar neighborhood, trading around $385 a share. For investors who have watched the software giant over the last few years, this is contested ground. The stock has pulled back about 5% from its one-month high, landing squarely in a price zone where buyers have mounted a defense three separate times. The question every watcher must now answer is a simple one: Will the floor hold again?

History makes a strong case for the bulls. The last three times Microsoft tested this level, the subsequent rallies produced peak…