Crowd Lap

THE LOOP IS YOUR ONLY BUFFER
A crowd is waiting. The buses are coming. Every passenger has a color, every bus has a color, and the only thing between them is one small looping road.
Tap a queue to send people out. They run onto the loop and start circling. When a bus of their color pulls in, they hop aboard and take a seat. Fill every seat and the bus drives away, making room for the next one.
Simple — until the loop fills up.
Anyone you release with nowhere to go stays out there. They circle. They take up space. They wait for a bus that might not arrive for a long, long time. Send out too many of the wrong color and the road jams solid: nobody can move, no bus can leave, and the level is lost.
So the real question is never "who can I send?" It's "who can I afford to send?"