House
One running application that is also a shelf of pieces to copy into another project. Never two copies of anything, and no folder of templates on the side: a piece is taken out of the live app, with a short recipe saying how to fit it.
Two rules
The app stays green: it builds, it runs, its tests pass. A piece that puts the app in the red is not a piece that is ready.
No second piece is added before the first has been copied into a real project or rehearsed end to end. The shelf grows by what was tried, not by what was written.