I have found an issue with both our mods. My mod has a debug scenery which hooks on on_player_created like your mod does and creates a debug world with all ruins being spawned. It works flawless when your mod is disabled. But once I enable your mod, I end up on a Foliax world in ghost mode and my needed hook on_player_created is never executed.

Can you please check if you can do something against it?

there is a setting to disable foliax starts, its probably two mods trying to do the same thing, at the same time

Yes, true but how can this be scripted that when the debug world is being loaded, your mod isn't doing anything?

you can force teleport the character back to your debug world, on first tick

script.on_event(defines.events.on_tick, function(event)
if event.tick == 1 and --whatever tells the script your debug setting is active-- then
local surface = game.surfaces["--whatever your surface name is--"]
local origin = { x = 0, y = 0 }

surface.request_to_generate_chunks(origin, 8)
surface.force_generate_chunk_requests()

player.teleport(origin, surface)

end
end

something like that should work, put in a check to make sure the debug is active