perf(verifier): memoize scopedElements per tree

scopedElements rebuilt a full tree walk plus map on every candidatesForVerb call (~16 per step). Cache the result keyed on lastTree and invalidate it in PushSnapshot.

internal/verifier/worker.go

@@ -35,6 +35,8 @@ type Verifier struct {
 	witnesses     map[string]Witness
 
 	lastTree       *hierarchy.Tree
+	scopeCache     map[*hierarchy.Element]bool
+	scopeCacheTree *hierarchy.Tree
 	lastAction     *Action
 	lastLogs       []LogEntry
 	lastExceptions []Exception
@@ -256,6 +258,7 @@ func (v *Verifier) buildFormulaNode(index int) (ltl.Formula, error) {
 // allowed and yields an empty ax scope.
 func (v *Verifier) PushSnapshot(input SnapshotInput) error {
 	v.lastTree = input.Tree
+	v.scopeCache = nil
 	v.lastAction = input.LastAction
 	v.lastLogs = input.Logs
 	v.lastExceptions = input.Exceptions
@@ -604,14 +607,16 @@ const frameworkPackage = "android"
 // With no app package configured (iOS/web, or an unscoped run) every node is in
 // scope, preserving prior behavior.
 func (v *Verifier) scopedElements() map[*hierarchy.Element]bool {
+	if v.scopeCacheTree == v.lastTree && v.scopeCache != nil {
+		return v.scopeCache
+	}
 	scope := make(map[*hierarchy.Element]bool, len(v.lastTree.Elements))
 	unscoped := v.appPackage == ""
 	if v.lastTree.Root == nil {
 		for _, element := range v.lastTree.Elements {
 			scope[element] = true
 		}
-		return scope
+	} else {
-	}
 		var walk func(node *hierarchy.Node, owner string)
 		walk = func(node *hierarchy.Node, owner string) {
 			if pkg := node.Element.Package; pkg != "" && pkg != frameworkPackage {
@@ -625,6 +630,9 @@ func (v *Verifier) scopedElements() map[*hierarchy.Element]bool {
 			}
 		}
 		walk(v.lastTree.Root, "")
+	}
+	v.scopeCache = scope
+	v.scopeCacheTree = v.lastTree
 	return scope
 }