Restore the Seam

OrderService below is untestable — it news up its storage directly, so no fake can stand in: ``csharp public sealed class OrderService // BROKEN — do not ship this { private readonly Dictionary<int, int> _d = new(); // hard-wired storage public int Bump(int id) { ... } } ` Refactor the *shape* the tests can see: 1. IStore { int Get(int id); void Put(int id, int v); } (inside Solution) 2. Solution.Service takes an IStore via constructor. 3. Service.Bump(id) adds Delta (a const int = 5) to the stored value and returns the new value. 4. Provide two adapters: DictStore (wraps a caller-supplied dictionary) and DoubleStore (its own private dictionary) — proving any implementation fits the same port. The tests inject each store in turn — the dependency points at a port, not an implementation. `csharp public static class Solution { public interface IStore { int Get(int id); void Put(int id, int v); } public sealed class DictStore : IStore; // wraps a supplied Dictionary<int,int> public sealed class DoubleStore : IStore; // independent private storage public sealed class Service // ctor(IStore); int Bump(int id) } ``