Spawn conditions

SpawnSystem requires enabled/biome membership, no corner-alt-biome name block, chance, required global/environment/day/night keys, population and spatial gates; persistent-event requirement checks the chosen center. Group quantity is capped by remaining capacity. Star chance includes biome-sector multiplier; positive world-level exponent branch caps the base at70 before sector multiplier. CreatureSpawner has different one-shot/respawn/time/noise/group gates; its requireSpawnArea field is not enforced here.