Composter zombie iron farm

A cheap tileable iron farm for three villagers and one zombie. The zombie sits in a composter below the villager platform and jumps, which keeps the villagers panicking, and the golems drop into lava over a single hopper. It uses natural terrain instead of digging, so it goes up in about five minutes, and it tiles at 32 block spacing for more output. Java only.

• Put open top trapdoors on the sides of the composter so the zombie pathfinds across them and jumps more often. Without this the farm stops after about half an hour, and this fixed it instantly for the builder who reported it.
• Getting the zombie into the composter is the hardest part of the build and a golem usually kills it first. Build walls up to the composter, and a golem already down in the hole cannot reach the zombie.
• Remove every bed and workstation within 48 blocks if golems will not spawn at all.
• A boat placed above the composter's level works in place of the composter. The zombie walks into it on the way to the villagers, and a mob in a boat never despawns, so no name tag is needed.
• A carved pumpkin on the zombie stops it burning and despawning, the other way around the name tag.
• Wandering trader llamas kill the zombie during long AFK sessions. It is worst in biomes with no other hostile spawns, because the trader hangs around instead of moving on.