Bug Report

Observed Behaviour
When upgrading the hammers, or at least when upgrading a stone hammer to an iron hammer, it requires a tier-2 hammer to be in my inventory... but it acts like I have no tier-2 hammers because its in the modification interface, with it saying that I only have tier-0 hammer. And yet, upgrading the handle works just fine.

Expected Behaviour
Should be able to upgrade the stone hammer to an iron hammer without issue.

Minimal setup needed to reproduce

• Forge version: 1.12.2 14.23.5.2847
• Tetra version: 0.39.1

Steps to reproduce

1. Put a stone hammer into the modification interface
2. Attempt to upgrade the left or right head to iron

Okay then, I assumed otherwise because I was able to upgrade the log hammer to a stone hammer without having a second hammer.

This is intended behaviour, wouldn't it be rather strange if you craft a tool using the tool itself?
You'll need two hammers :)