Fertilized eggs ruined by temperature are still "fertilized eggs"; it has been reported several times (here on forums, on discord and so on).
That thing make very difficult to use ruined fertilized eggs for cooking, because they cannot be discriminate from "not-ruined" fertilized eggs.
I know there's a mod (Animal logic IIRC) that forces ruined fertilized eggs to be converted to unfertilized ones but my idea is different: simply add a filter to allow/disallow "ruined by temperature" items, without converting them.
We already have "tainted", "rotten/fresh", "smeltable/not smeltable", etc filters
If I got it correctly it could be done with a class derived by SpecialThingFilterWorker class but I've no ideas about how to really implement it from scratch.
I found a similar implementation of derived class here (https://github.com/notfood/RimWorld-Infused/blob/master/Source/SpecialThingFilterWorker_Infused.cs) but I need to study how that modder used it
edit: I think I did it but I'd like a review about code (I think it's okay, after all it's quite simple) and functionality (default values, allowing filtering for ruined and not ruined or ruined only, etc)
I'm attaching here code and output, if anyone would like to comment.
@mods: maybe you could move this topic in the most appropriate section
edit: mod released, see here (https://ludeon.com/forums/index.php?topic=54692.0)