fix: improve unowned derived performance (#14724)

* fix: improve unowned derived performance

* fix: improve unowned derived performance

* changeset

.changeset/many-worms-attend.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: improve unowned derived performance

packages/svelte/src/internal/client/runtime.js

@@ -230,8 +230,9 @@ export function check_dirtiness(reaction) {
 			}
 		}
 
-		// Unowned signals should never be marked as clean.
+		// Unowned signals should never be marked as clean unless they
-		if (!is_unowned) {
+		// are used within an active_effect without skip_reaction
+		if (!is_unowned || (active_effect !== null && !skip_reaction)) {
 			set_signal_status(reaction, CLEAN);
 		}
 	}