Use entry metadata for resolution presence

internal/engine/resolution.go

@@ -13,7 +13,6 @@ const closedCallbackContextMessage = "configkit: callback context is no longer a
 type resolutionState struct {
 	active      bool
 	schema      *schemaDescriptor
-	presence    map[string]inputPresence
 	document    *document.Node
 	input       resolutionInput
 	records     map[string]*resolutionRecord
@@ -78,8 +77,12 @@ func (r *Resolution) IsExplicit(path Path) bool {
 	if !state.validPath(path) {
 		return false
 	}
-	_, explicit := state.presence[path.String()]
-	return explicit
+	return state.inputExplicit(path)
+}
+
+func (state *resolutionState) inputExplicit(path Path) bool {
+	info, found := state.input.lookup(path)
+	return found && info.Explicit
 }
 
 // InputInfo returns detached entry-state metadata for path. The entry state is
@@ -134,7 +137,7 @@ func Default[V any](resolution *Resolution, path Path, target *V, value V, reaso
 	if !ok {
 		return
 	}
-	if _, explicit := state.presence[path.String()]; explicit {
+	if state.inputExplicit(path) {
 		return
 	}
 	*target = value
@@ -282,7 +285,7 @@ func (state *resolutionState) addDiagnostic(code Code, path Path, message string
 
 func runResolution[T any](configuration *T, resolver func(*T, *Resolution) error, schema *schemaDescriptor, decoded decodedConfiguration, input *document.Node, entry resolutionInput) resolutionResult {
 	state := &resolutionState{
-		active: true, schema: schema, presence: decoded.presence, document: input,
+		active: true, schema: schema, document: input,
 		input:   entry,
 		records: make(map[string]*resolutionRecord),
 	}