fix: correctly transform `$derived` private fields on server (#16894)

Closes #16889

.changeset/seven-flies-drop.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: correctly transform `$derived` private fields on server

packages/svelte/src/compiler/phases/3-transform/server/visitors/MemberExpression.js

@@ -7,11 +7,7 @@ import * as b from '#compiler/builders';
  * @param {Context} context
  */
 export function MemberExpression(node, context) {
-	if (
+	if (context.state.analysis.runes && node.property.type === 'PrivateIdentifier') {
-		context.state.analysis.runes &&
-		node.object.type === 'ThisExpression' &&
-		node.property.type === 'PrivateIdentifier'
-	) {
 		const field = context.state.state_fields?.get(`#${node.property.name}`);
 
 		if (field?.type === '$derived' || field?.type === '$derived.by') {

packages/svelte/tests/runtime-runes/samples/class-state-derived-private/main.svelte

@@ -9,7 +9,8 @@
 		}
 
 		get embiggened1() {
-			return this.#doubled;
+			const self = this;
+			return self.#doubled;
 		}
 
 		get embiggened2() {