fix: allow one "window" for each renderer

packages/svelte/src/internal/client/custom-renderer/state.js

@@ -7,8 +7,8 @@
  */
 export let renderer = null;
 
-// to use with $props.id()
-export let custom_renderer_window = {};
+// allow for a "window" for each custom renderer...to use with `$props.id`
+export let custom_renderer_window_map = new WeakMap();
 
 /**
  * @param {Renderer<any, any, any, any> | null} $renderer

packages/svelte/src/internal/client/dom/operations.js

@@ -13,7 +13,7 @@ import {
 } from '#client/constants';
 import { eager_block_effects } from '../reactivity/batch.js';
 import { NAMESPACE_HTML } from '../../../constants.js';
-import { custom_renderer_window, renderer } from '../custom-renderer/state.js';
+import { custom_renderer_window_map, renderer } from '../custom-renderer/state.js';
 
 // export these for reference in the compiled code, making global name deduplication unnecessary
 /** @type {Window} */
@@ -791,6 +791,11 @@ export function class_list_toggle(element, name, force) {
 
 export function get_window() {
 	if (renderer) {
+		var custom_renderer_window = custom_renderer_window_map.get(renderer);
+		if (!custom_renderer_window) {
+			custom_renderer_window = {};
+			custom_renderer_window_map.set(renderer, custom_renderer_window);
+		}
 		return custom_renderer_window;
 	}
 	return window;

packages/svelte/src/internal/client/dom/template.js

@@ -420,9 +420,8 @@ export function props_id() {
 
 	let window = get_window();
 
-	// @ts-expect-error This way we ensure the id is unique even across Svelte runtimes
+	// This way we ensure the id is unique even across Svelte runtimes
 	(window.__svelte ??= {}).uid ??= 1;
 
-	// @ts-expect-error
 	return `c${window.__svelte.uid++}`;
 }