Somehow, my blacksmith wasn’t producing enough heavy tools to keep buildings supplied, so I shut down everything that was idling waiting on heavy tools. Then I bought two of them, as I was also unable to produce iron. I expected the forge to take one and the foundry to take the other as these are the only two buildings I reactivated after buying the heavy tools. As it turns out, the blacksmith put one on their machines and one in storage. Now my inventory shows no heavy tools in storage, and the forge can’t retrieve one from the blacksmith, even after shutting the blacksmith down and cycling the forge off and on again.
Edit: As it turns out, the Mill also will store a heavy tool even though it has one in use and this storage is not counted as part of the global storage. I guess this is so people don’t keep stealing from other shops only to stock up their own storage. I still think the immediate needs should be able to take priority over any storage needs though.
Edit 2: After buying two heavy tools again, and disabling every other building that even uses them, I watched the foundry workers as they stocked them. I noticed that when one is put on the machine, it also counts as being in storage. This is misleading. So from what I can tell, the heavy tools I thought were being hoarded by other buildings are actually in use.
What should happen: Buildings that use heavy tools should not show it in storage if it doesn’t count towards the global storage pool, just as buildings that require materials to be upgraded remove those materials from the pool when they are set aside. This should also count for other materials needed for any kind of production. The current job should remove a count from that buildings storage while the product is being produced. Maybe set it in another slot or something in case you lose the worker and another has to come back to finish the job using that already borrowed material. For instance, if a unit of iron is needed to make something, and the work on that item is halfway done, that iron is no longer available to reuse anywhere else, so why list it in the storage of that building?