We know how this story turns out, but it’s still fun to watch 244 years later. Hundreds of spectators braved a drizzle on Lexington Green on Monday morning to witness the annual Patriots Day reenactment of “the shot heard round the world,’’ the first major conflict of the Revolutionary War. Just after dawn, the British regulars appeared, decked in Lobster red. Rank after rank marched onto the Common. Captain John Parker, who led the colonial militia, bellowed: “Steady, men!” There followed a shot of unknown provenance, followed by a barrage of musket fire that left eight Massachusetts men dead.