Prevent us from returning false for updating suspended vnode trees

.changeset/fuzzy-ads-poke.md

@@ -0,0 +1,5 @@
+---
+"@preact/signals": patch
+---
+
+Fix issue where unmounted vnodes could update with signals

packages/preact/src/index.ts

@@ -363,6 +363,9 @@ Component.prototype.shouldComponentUpdate = function (
 	props,
 	state
 ) {
+	// Suspended vnodes should always update:
+	if (this.__R) return true;
+
 	// @todo: Once preactjs/preact#3671 lands, this could just use `currentUpdater`:
 	const updater = this._updater;
 	const hasSignals = updater && updater._sources !== undefined;

packages/preact/src/internal.d.ts

@@ -21,6 +21,8 @@ export interface AugmentedElement extends HTMLElement {
 }
 
 export interface AugmentedComponent extends Component<any, any> {
+	// onResolve --> Preact indicator for suspended subtrees
+	__R?: boolean;
 	//  hasScuFromHooks
 	// Preact 10.12 - Preact 10.25
 	u?: boolean;