MultiChildSeed class abstract

A Seed that carries a fixed, ordered list of child seeds directly in its configuration — the MultiChildRenderObjectWidget analogue, and the multi-child sibling of the single-child component seeds (StatelessSeed/StatefulSeed/Sprout).

A component seed builds one child from a build() method; a MultiChildSeed instead declares its children up front. Its MultiChildBranch keyed-reconciles them against the previous set on every rebuild (Branch.updateChildren): a child matched by key (or, when unkeyed, by position) keeps its branch identity across rebuilds; a child that appears mounts; a child that vanishes unmounts; and the resulting child order follows children. The identical-config fast path is inherited unchanged — a child seed reused by identical instance prunes its subtree at reconcile time.

MultiChildSeed is abstract deliberately: a seed's runtimeType is its reconciliation tag (Seed.canUpdate), so a topology of distinct container kinds (e.g. a Grid of Rigs of Steps) must subclass it once per kind — two kinds sharing this base directly would reconcile into one another. Subclasses pass their children up and may add their own typed fields:

class Grid extends MultiChildSeed {
  const Grid(List<Rig> rigs) : super(children: rigs);
}