The whole case turns on one CT finding: the contrast blush. A blush is a focal bright spot of contrast inside or around the spleen, and it means an artery is actively leaking or has formed a pseudoaneurysm. Start with the version that has no blush. Here the patient is young, stable, and FAST positive but the bleeding is not active, so the safest plan is to watch him closely without surgery, which is conservative management. Now switch to the version with a blush. The patient is still stable, but the blush proves bleeding is continuing, so simply observing him risks a sudden deterioration. At the same time we want to keep his spleen for immune protection. The procedure that does both, stopping the arterial bleed while sparing the organ, is splenic artery embolization done through angiography. Open surgery, whether removing the spleen or repairing it, is held back for patients who become unstable or who fail the non-operative route. So the management asked for in the blush scenario is angioembolization.\[\boxed{\text{Splenic artery embolization}}\]