You take an idea that’s not all that original and implement it on a computer. For that, the Supreme Court ruled unanimously Thursday, you don’t deserve a patent. Seeking to do its part to trim the proliferation of software patents, the high court nevertheless tread carefully to avoid ensnaring too many legitimate patents along the way. The case had attracted legions of lawyers on both sides to the high court’s chamber in March, as well as hundreds of pages of briefs from the likes of Google, Microsoft and IBM. Many had urged a solution similar to what the justices sought to devise Thursday: a reduction in flimsy patents without affecting the deserving ones. The specific patent in question uses a computer to safeguard complex financial transactions, largely among banks. The program is intended to reduce the risk that one party can’t hold up its end of the deal.