fix: don't clone non-proxies in `$inspect` (#16617)

* fix: don't clone non-proxies in `$inspect`

* apply suggestion

* lint

.changeset/itchy-games-guess.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: don't clone non-proxies in `$inspect`

packages/svelte/src/internal/shared/clone.js

@@ -15,14 +15,15 @@ const empty = [];
  * @template T
  * @param {T} value
  * @param {boolean} [skip_warning]
+ * @param {boolean} [no_tojson]
  * @returns {Snapshot<T>}
  */
-export function snapshot(value, skip_warning = false) {
+export function snapshot(value, skip_warning = false, no_tojson = false) {
 	if (DEV && !skip_warning) {
 		/** @type {string[]} */
 		const paths = [];
 
-		const copy = clone(value, new Map(), '', paths);
+		const copy = clone(value, new Map(), '', paths, null, no_tojson);
 		if (paths.length === 1 && paths[0] === '') {
 			// value could not be cloned
 			w.state_snapshot_uncloneable();
@@ -40,7 +41,7 @@ export function snapshot(value, skip_warning = false) {
 		return copy;
 	}
 
-	return clone(value, new Map(), '', empty);
+	return clone(value, new Map(), '', empty, null, no_tojson);
 }
 
 /**
@@ -49,10 +50,11 @@ export function snapshot(value, skip_warning = false) {
  * @param {Map<T, Snapshot<T>>} cloned
  * @param {string} path
  * @param {string[]} paths
- * @param {null | T} original The original value, if `value` was produced from a `toJSON` call
+ * @param {null | T} [original] The original value, if `value` was produced from a `toJSON` call
+ * @param {boolean} [no_tojson]
  * @returns {Snapshot<T>}
  */
-function clone(value, cloned, path, paths, original = null) {
+function clone(value, cloned, path, paths, original = null, no_tojson = false) {
 	if (typeof value === 'object' && value !== null) {
 		var unwrapped = cloned.get(value);
 		if (unwrapped !== undefined) return unwrapped;
@@ -71,7 +73,7 @@ function clone(value, cloned, path, paths, original = null) {
 			for (var i = 0; i < value.length; i += 1) {
 				var element = value[i];
 				if (i in value) {
-					copy[i] = clone(element, cloned, DEV ? `${path}[${i}]` : path, paths);
+					copy[i] = clone(element, cloned, DEV ? `${path}[${i}]` : path, paths, null, no_tojson);
 				}
 			}
 
@@ -88,8 +90,15 @@ function clone(value, cloned, path, paths, original = null) {
 			}
 
 			for (var key in value) {
+				copy[key] = clone(
 					// @ts-expect-error
-				copy[key] = clone(value[key], cloned, DEV ? `${path}.${key}` : path, paths);
+					value[key],
+					cloned,
+					DEV ? `${path}.${key}` : path,
+					paths,
+					null,
+					no_tojson
+				);
 			}
 
 			return copy;
@@ -99,7 +108,7 @@ function clone(value, cloned, path, paths, original = null) {
 			return /** @type {Snapshot<T>} */ (structuredClone(value));
 		}
 
-		if (typeof (/** @type {T & { toJSON?: any } } */ (value).toJSON) === 'function') {
+		if (typeof (/** @type {T & { toJSON?: any } } */ (value).toJSON) === 'function' && !no_tojson) {
 			return clone(
 				/** @type {T & { toJSON(): any } } */ (value).toJSON(),
 				cloned,