fix: use local mutable sources for props in legacy mode in case they are indirectly invalidated

Author: Rich-Harris

.changeset/orange-tips-pull.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: use local mutable sources for props in legacy mode in case they are indirectly invalidated

packages/svelte/src/internal/client/reactivity/props.js

@@ -335,7 +335,7 @@ export function prop(props, key, flags, fallback) {
 	}
 
 	// easy mode — prop is never written to
-	if ((flags & PROPS_IS_UPDATED) === 0) {
+	if ((flags & PROPS_IS_UPDATED) === 0 && runes) {
 		return getter;
 	}