Would it be possible to add support for the blueprint sandbox mod [1] and disable warnings in case the player is inside a sandbox? Missing items are created instantly and don't need warning.

[1] https://mods.factorio.com/mod/blueprint-sandboxes

Thanks for the suggestion, this should definitely be possible!

Hey, I had a look at this, and I can't get warnings to trigger in the sandbox at all using that mod. Without reproduction steps unfortunately I can't really fix it... even looking at the mod settings I couldn't find something that looked like it would trigger this behaviour. Let me know if you've got further suggestions on how I could reproduce this issue.

Thank you for looking into this issue!

I can reproduce the warning with the following steps:
1. Have the default settings, i.e. "Enable ghost warnings: On"
2. Hold any ghost item (make sure you don't have the actual item in your inventory. For example by selecting a new item in the crafting menu with Q)
3. Place ghost in the sandbox
Result: A warning will be displayed "Missing <item name>"

FWIW, this quick hack would fix the problem:
control.lua L80:
-- ignore blueprint sandbox
if player.gui.left["bpsb-toggle-gui"].visible then return end