Ice and Fire Siren Addon (1.21.1)

• Adds lagoon generation for sirens in every dimension. Roughly every 10 seconds per world, a random nearby chunk (within ~96 blocks of a non-spectator player) is chosen to host a small lagoon.
• Lagoons carve a 20–30 block deep, radius 4 water pool with a grassy floor and shore; a siren is spawned in the pool when the Ice and Fire Community Edition siren entity is present.
• In the Nether, lava inside and around the lagoon is replaced with water and nether blocks (netherrack and nether brick variants) around the lagoon are swapped to grass to make a calm spawning area.
• Each chunk is only processed once per server run to prevent repeated carving; lagoons respect world borders.
• If the siren entity is missing, the mod logs a one-time warning and skips spawning (lagoon creation still occurs).

Known limits / tips:

• Lagoon attempts are not persisted between restarts, so already visited chunks can be reprocessed after a reboot.
• Nether water is force-placed; other mods that remove water in the Nether may counteract the pools.