fix: maintain reactivity for properties of deriveds with no deps

fixes #17111, fixes #17352

Author: hmnd

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

@@ -360,7 +360,9 @@ export function update_derived(derived) {
 		// the underlying value will be updated when the fork is committed.
 		// otherwise, the next time we get here after a 'real world' state
 		// change, `derived.equals` may incorrectly return `true`
-		if (!current_batch?.is_fork) {
+		// Exception: deriveds with no deps should always update `derived.v`
+		// since they will never change and need the value after fork commits
+		if (!current_batch?.is_fork || derived.deps === null) {
 			derived.v = value;
 		}
 
@@ -381,6 +383,11 @@ export function update_derived(derived) {
 		if (effect_tracking() || current_batch?.is_fork) {
 			batch_values.set(derived, value);
 		}
+		// For deriveds with no deps, set CLEAN to prevent re-evaluation
+		// since they can never become dirty from dependency changes
+		if (derived.deps === null) {
+			set_signal_status(derived, CLEAN);
+		}
 	} else {
 		var status = (derived.f & CONNECTED) === 0 ? MAYBE_DIRTY : CLEAN;
 		set_signal_status(derived, status);