refactor(hierarchy): one Tree.Transitional, drop the duplicated cross-fade check

internal/runner/runner.go

@@ -878,7 +878,7 @@ retryLoop:
 			tree, err = hierarchy.Parse(hierarchyJSON)
 			pngBytes = image.PNG
 		}
-		if err != nil || !isTransitionalHierarchy(tree) {
+		if err != nil || !tree.Transitional() {
 			break
 		}
 		// A tree unchanged since the previous attempt is a settled state
@@ -909,27 +909,6 @@ retryLoop:
 	return tree, pngBytes, transitional, err
 }
 
-// isTransitionalHierarchy returns true when the tree carries more than one
-// resource-id ending in "Screen" - the marker of a Compose NavHost mid
-// cross-fade where both source and destination route composables are alive.
-// Mirrors the sidecar's stabilitySnapshot heuristic so runner-side rejection
-// stays consistent with the settle poll.
-func isTransitionalHierarchy(tree *hierarchy.Tree) bool {
-	if tree == nil {
-		return false
-	}
-	screens := 0
-	for _, element := range tree.Elements {
-		if strings.HasSuffix(element.ResourceID, "Screen") {
-			screens++
-			if screens > 1 {
-				return true
-			}
-		}
-	}
-	return false
-}
-
 func traceActionFor(action verifier.Action, tree *hierarchy.Tree) *trace.Action {
 	traceAction := &trace.Action{Kind: string(action.Kind), X: action.X, Y: action.Y}
 	switch action.Kind {

internal/runner/runner_test.go

@@ -1118,34 +1118,6 @@ func TestRunner_OneScreenshotPerStep(t *testing.T) {
 	}
 }
 
-// TestIsTransitionalHierarchy_DetectsMultipleScreens covers the runner-side
-// guard that re-fetches when the hierarchy still carries two route-level
-// *Screen ids - the NavHost cross-fade signature.
-func TestIsTransitionalHierarchy_DetectsMultipleScreens(t *testing.T) {
-	multi, err := hierarchy.Parse(`{"attributes":{"resource-id":"root"},"children":[
-	  {"attributes":{"resource-id":"AddAccountScreen"},"children":[]},
-	  {"attributes":{"resource-id":"HomeScreen"},"children":[]}
-	]}`)
-	if err != nil {
-		t.Fatal(err)
-	}
-	if !isTransitionalHierarchy(multi) {
-		t.Error("expected multi-screen tree to be flagged as transitional")
-	}
-
-	single, err := hierarchy.Parse(`{"attributes":{"resource-id":"HomeScreen"},"children":[]}`)
-	if err != nil {
-		t.Fatal(err)
-	}
-	if isTransitionalHierarchy(single) {
-		t.Error("single-screen tree must not be flagged as transitional")
-	}
-
-	if isTransitionalHierarchy(nil) {
-		t.Error("nil tree must not be flagged as transitional")
-	}
-}
-
 // TestRunner_StableTransitionalTreeIsVerified feeds a driver whose hierarchy
 // constantly carries two route-level *Screen ids but never changes between
 // retry attempts. Such a tree is a settled state that merely matches the