2. Replenish formation: Formations when built will "remember" their original formation and the units in it will be listed as 100/100 or 48/100 of the original formations units. Any elements added by facilities or manually by drag moving will just be 100 or 48. A ground force facility will be able to Replenish formation these back to full as a task. Same as above with the formation still being
I would recommend that its not a "remember" thing and more a "build to template" thing. Imagine that somewhere in the UI is a dropdown selection with your designed formations, you select the formation you want to replenish and then select the target formation to build to. This will do two things:
1 - Create a "one-off" template that has all the missing units that need to be added and add it to the GU build queue, the new units either immediately join their intended formation or are dropped into their own formation which can be merged. IMO in the case of the latter there should be some sort of "merge" button that allows the player to instantly merge all units between two formations.
2 - There may be units that are not in the target template that are in the template that is being "retrofitted", these units are separated into their own "surplus" formation and appear on the OOB as an independent formation which can be re-organized somewhere else. If the target has no common units this might result in the retrofitted formation being temporarily empty.