Replay explanations through shared history selections

internal/engine/explain_test.go

@@ -389,6 +389,11 @@ func TestExplanationReconcilesDefaultsAfterInputReplacement(t *testing.T) {
 					if last.Origin.Layer != info.Origin.Layer {
 						t.Fatal("decoding lost effective origin")
 					}
+					for _, metadataChange := range result.Metadata().History(path) {
+						if metadataChange.Origin.Operation == ChangeDecoding {
+							t.Fatal("typed reconciliation leaked into metadata history")
+						}
+					}
 				}
 			})
 		}
@@ -535,6 +540,25 @@ func TestExplanationReplaysResolutionAdditionsAndOverlappingIntent(t *testing.T)
 				if overlap && count != 1 {
 					t.Fatalf("overlapping records applied %d times", count)
 				}
+				if overlap && path.String() == "/m" {
+					metadataHistory := result.Metadata().History(path)
+					var sharedResolutionOrigin bool
+					for _, metadataChange := range metadataHistory {
+						if metadataChange.Origin.Layer != LayerResolution {
+							continue
+						}
+						for _, explanationChange := range x.History {
+							if explanationChange.Origin.Layer == metadataChange.Origin.Layer &&
+								explanationChange.Origin.Operation == metadataChange.Origin.Operation &&
+								reflect.DeepEqual(explanationChange.Origin.Locations, metadataChange.Origin.Locations) {
+								sharedResolutionOrigin = true
+							}
+						}
+					}
+					if !sharedResolutionOrigin {
+						t.Fatalf("metadata and explanation disagree on overlapping resolution attribution: metadata %#v, explanation %#v", metadataHistory, x.History)
+					}
+				}
 				last := x.History[len(x.History)-1]
 				if last.After != x.Effective {
 					t.Fatalf("incorrect replay for %s: %#v", path, x)