Each building would have (up to) 4 job options (right-click hold menu) as follows:
Supply: Anyone with this job will try to keep the building fully supplied (gathering items from storage around the base and keeping the building's supply hopper full).
Harvest: Collects the building's output whenever possible.
Use: Just uses, doesn't try to supply/harvest (though perhaps will supply/harvest from/to their own inventory, right near by storage that doesn't require movement, etc - this option could be set in the AI settings. The main point is that the character doesn't leave their post as long as there is a job to be done, and doesn't try to harvest/stash, but just keeps plugging away or moves on if there's another job - potentially filling up say 10 machines and just keeping them full as input supplies get put in the machine/output space become available...)
Work: basically a shortcut (to reduce job list clutter) for "supply, use, harvest" (basically the current job functionality.
Why this is needed? Because automatic machines (that require no workers) have issues right now that this would not only totally resolve, but that would also make much clearer to the player (no "use" option? oh this must be an automatic machine! -completely and instantly obvious how the machine is operated.)
Secondarily, streamlining options for the player. Want one guy just running around supplying/harvesting? No problem, you can. Want a guy to make armor plates and feed them to the armor smith, but don't want that guy actually making armor? No problem...
Further, you could have "deposit only" or "withdrawal only" type storage (for instance to keep a supply of metal plates around). Just don't have anyone set to harvest from that storage unit and it'll never get taken from except manually...
Etc. etc.
Also, it'd standardize the job list and make things clearer. And a clear consistent UI is the best UI
PS: The building settings in the FCS could determine which jobs are available or it could be automatically determined/inferred from the facts that the building has zero workers, no input/output inventory, etc....