An Assembly Item, the same as any inventory item, is not Job Tracked. It's not direct and unique, but Stocked in anticipation of sales to the job or use on the job. So, the function of Inventory = having it on hand and ready.

Then, later, you Sell it, or you use Adjust inventory and in this screen you Job Track that this is relieved from stock directly for a specific job but not being Sold to that job.

The Build Assembly is Not the Job tracked stage. This is the Creation Stage.

For Noninventory two-sided items, you job track them at the time of the purchase. For inventory, which includes Assembly Item on hand, not the Build phase but Now available, that is the Sale or the Adjustment function, that creates the Costing event.

You will see this on the Job Cost reports, as long as you remove the Account filter that is "ordinary income/expense" to see Job Profitability Detail, for instance, include the adjustment in Costs.

Please see my attached Job Cost report.