A quick note about ongoing saves: there shouldn't be any major problems with ongoing saves but if any Shellworlds were under construction or upgrading when you last saved then the relevant situations may not accurately display progress due to the changes in construction time. This won't break anything gameplay-wise, and new constructions will be displayed properly.

FEATURES:
-You can now choose between a mining, generator, food, or balanced focus when constructing shellworlds. This will cause more of the designated resources to spawn.

-Gas Giants can spawn with the Oxygen Rich modifier, these allow the gas giant to be harvested twice

-Settings to disable Shellworlds for AI empires. This will prevent the AI from taking the Shellworld Ascension Perk or using the construction Decision. If the AI is disabled after they have constructed a Shellworld they will still be able to upgrade those Shellworlds.

BALANCE:
-increased build cost to 7500, upgrade cost to 2000
-decreased the initial shellworld construction time from 10 years to 5 years, and increased the upgrade time to 2 years
-Shellworlds Ascension Perk now requires 2 previously unlocked Perks instead of 1

QOL/MODDING:
-oxygen harvester station building can no longer be built in systems that have already depleted their gas giants
-added is_valid_shellworld_country for mod compatibility purposes, checks if empire has a forbid_shellworld flag and prevents that empire from using the Shellworld AP if it does
-added scripted triggers for is_oxygen_source and is_valid_shellworld_candidate
-adjusted a few tooltips and modifier icons to make mechanics more clear