Feature Unit

A FeatureUnit ties a Feature to an ExcavationUnit. Because a single feature — like a hearth, wall, or pit — can extend across more than one excavation unit, and a unit can expose more than one feature, the link between them is many-to-many. Each FeatureUnit row is one such connection, identified by its featureId and excavationUnitId, and records when the link was made through createdAt. This lets the system answer which units a feature spans and which features were found in a given unit, keeping spatial relationships across the dig accurate.