Add shared-root publish planning

internal/state/shared_root_test.go

@@ -200,6 +200,38 @@ func TestSharedRootOwnerOutputHelpersRejectConflicts(t *testing.T) {
 	}
 }
 
+func TestCompareSharedRootOwnerScopesCurrentOwner(t *testing.T) {
+	state := validSharedRootState(t)
+	source := validManifest(t)
+	source.Created = source.Created.Add(time.Hour)
+	scope := CurrentOwnerScope("reports", "archive")
+
+	comparison := CompareSharedRootOwner(source, scope, DestinationStatus{SharedRoot: &state, HasContents: true})
+	if comparison.Outcome != OutcomeDestinationOlder {
+		t.Fatalf("comparison = %#v, want destination older for current owner", comparison)
+	}
+
+	missing := CompareSharedRootOwner(source, CurrentOwnerScope("missing", "archive"), DestinationStatus{SharedRoot: &state, HasContents: true})
+	if missing.Outcome != OutcomeDestinationAbsent {
+		t.Fatalf("missing owner comparison = %#v, want destination absent", missing)
+	}
+}
+
+func TestCompareSharedRootOwnerAcceptsMatchingSingleOwnerState(t *testing.T) {
+	singleOwner, err := Parse([]byte(validStateJSON(t)))
+	if err != nil {
+		t.Fatalf("Parse() error = %v", err)
+	}
+	source := singleOwner.Source.Manifest
+	source.Created = source.Created.Add(time.Hour)
+	scope := CurrentOwnerScope(singleOwner.PipelineID, singleOwner.DestinationID)
+
+	comparison := CompareSharedRootOwner(source, scope, DestinationStatus{State: &singleOwner, HasContents: true})
+	if comparison.Outcome != OutcomeDestinationOlder {
+		t.Fatalf("comparison = %#v, want destination older", comparison)
+	}
+}
+
 func validSharedRootStateJSON(t *testing.T) string {
 	t.Helper()
 	data, err := json.MarshalIndent(validSharedRootState(t), "", "  ")