Define adapter interfaces and fake implementations

internal/adapters/storage/fake.go

@@ -0,0 +1,40 @@
+package storage
+
+import "context"
+
+// NoopBackend is a deterministic no-op archive/storage adapter.
+type NoopBackend struct{}
+
+// Archive returns the requested items as archived with placeholder metadata.
+func (n *NoopBackend) Archive(ctx context.Context, req ArchiveRequest) (ArchiveResult, error) {
+	if err := ctx.Err(); err != nil {
+		return ArchiveResult{}, err
+	}
+	return ArchiveResult{Archived: append([]ArchiveItem(nil), req.Items...), Metadata: map[string]any{"placeholder": true}}, nil
+}
+
+// FakeBackend captures archive requests and returns deterministic responses.
+type FakeBackend struct {
+	Requests []ArchiveRequest
+	Err      error
+	Result   ArchiveResult
+}
+
+// Archive records request and returns configured response.
+func (f *FakeBackend) Archive(ctx context.Context, req ArchiveRequest) (ArchiveResult, error) {
+	if err := ctx.Err(); err != nil {
+		return ArchiveResult{}, err
+	}
+	f.Requests = append(f.Requests, req)
+	if f.Err != nil {
+		return ArchiveResult{}, f.Err
+	}
+	res := f.Result
+	if res.Archived == nil {
+		res.Archived = append([]ArchiveItem(nil), req.Items...)
+	}
+	if res.Metadata == nil {
+		res.Metadata = map[string]any{"fake": true}
+	}
+	return res, nil
+}