From 75c448cb72975b80946f9caa7c4fcb15d2845ef7 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Tue, 10 Jun 2025 14:18:28 -0400
Subject: [PATCH 01/12] remove PROXY_REMOVE_PATH

---
 .../client/visitors/VariableDeclaration.js    | 25 +++++++------------
 .../svelte/src/internal/client/constants.js   |  2 --
 packages/svelte/src/internal/client/proxy.js  |  1 -
 .../src/internal/client/reactivity/sources.js |  7 ++----
 4 files changed, 11 insertions(+), 24 deletions(-)

diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/VariableDeclaration.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/VariableDeclaration.js
index 13869229b5b4..b531f0df6e41 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/VariableDeclaration.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/VariableDeclaration.js
@@ -9,7 +9,6 @@ import { get_rune } from '../../../scope.js';
 import { get_prop_source, is_prop_source, is_state_source, should_proxy } from '../utils.js';
 import { is_hoisted_function } from '../../utils.js';
 import { get_value } from './shared/declarations.js';
-import { PROXY_REMOVE_PATH } from '#client/constants';
 
 /**
  * @param {VariableDeclaration} node
@@ -90,12 +89,7 @@ export function VariableDeclaration(node, context) {
 								binding.kind === 'bindable_prop' &&
 								should_proxy(initial, context.state.scope)
 							) {
-								initial = b.call(
-									'$.proxy',
-									initial,
-									dev ? b.literal(id.name) : undefined,
-									dev ? b.literal(PROXY_REMOVE_PATH) : undefined
-								);
+								initial = b.call('$.proxy', initial, dev ? b.literal(id.name) : undefined);
 							}
 
 							if (is_prop_source(binding, context.state)) {
@@ -136,20 +130,19 @@ export function VariableDeclaration(node, context) {
 					);
 					const is_state = is_state_source(binding, context.state.analysis);
 					const is_proxy = should_proxy(value, context.state.scope);
+
 					if (rune === '$state' && is_proxy) {
-						value = b.call(
-							'$.proxy',
-							value,
-							dev ? b.literal(id.name) : undefined,
-							dev ? b.literal(PROXY_REMOVE_PATH) : undefined
-						);
+						value = b.call('$.proxy', value, dev ? b.literal(id.name) : undefined);
 					}
+
 					if (is_state) {
 						value = b.call('$.state', value);
+
+						if (dev) {
+							value = b.call('$.tag', value, b.literal(id.name));
+						}
 					}
-					if (dev && is_state) {
-						value = b.call('$.tag', value, b.literal(id.name));
-					}
+
 					return value;
 				};
 
diff --git a/packages/svelte/src/internal/client/constants.js b/packages/svelte/src/internal/client/constants.js
index 98695bf75107..268ba29c883a 100644
--- a/packages/svelte/src/internal/client/constants.js
+++ b/packages/svelte/src/internal/client/constants.js
@@ -27,8 +27,6 @@ export const EFFECT_IS_UPDATING = 1 << 21;
 export const PROXY_PRESERVE_PATH = 1 << 1;
 /** Change proxy path to new "owner" */
 export const PROXY_CHANGE_PATH = 1 << 2;
-/** "Unown" proxy, so its path becomes `[$state proxy]` */
-export const PROXY_REMOVE_PATH = 1 << 3;
 
 export const STATE_SYMBOL = Symbol('$state');
 export const LEGACY_PROPS = Symbol('legacy props');
diff --git a/packages/svelte/src/internal/client/proxy.js b/packages/svelte/src/internal/client/proxy.js
index 993c6f45a27c..6237655e4922 100644
--- a/packages/svelte/src/internal/client/proxy.js
+++ b/packages/svelte/src/internal/client/proxy.js
@@ -13,7 +13,6 @@ import {
 	PROXY_CHANGE_PATH,
 	PROXY_PATH_SYMBOL,
 	PROXY_PRESERVE_PATH,
-	PROXY_REMOVE_PATH,
 	STATE_SYMBOL
 } from '#client/constants';
 import { UNINITIALIZED } from '../../constants.js';
diff --git a/packages/svelte/src/internal/client/reactivity/sources.js b/packages/svelte/src/internal/client/reactivity/sources.js
index 847f14d2eca9..ad5ad3383d14 100644
--- a/packages/svelte/src/internal/client/reactivity/sources.js
+++ b/packages/svelte/src/internal/client/reactivity/sources.js
@@ -27,8 +27,7 @@ import {
 	UNOWNED,
 	MAYBE_DIRTY,
 	BLOCK_EFFECT,
-	ROOT_EFFECT,
-	PROXY_REMOVE_PATH
+	ROOT_EFFECT
 } from '#client/constants';
 import * as e from '../errors.js';
 import { legacy_mode_flag, tracing_mode_flag } from '../../flags/index.js';
@@ -140,9 +139,7 @@ export function set(source, value, should_proxy = false) {
 		e.state_unsafe_mutation();
 	}
 
-	let new_value = should_proxy
-		? proxy(value, DEV ? source.trace_name : undefined, DEV ? PROXY_REMOVE_PATH : undefined)
-		: value;
+	let new_value = should_proxy ? proxy(value, DEV ? source.trace_name : undefined) : value;
 
 	return internal_set(source, new_value);
 }

From 4e7f26101dfd08e649af83954bc30c0529ea44cb Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Tue, 10 Jun 2025 14:39:51 -0400
Subject: [PATCH 02/12] simplify a bit

---
 packages/svelte/src/internal/client/proxy.js | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/packages/svelte/src/internal/client/proxy.js b/packages/svelte/src/internal/client/proxy.js
index 6237655e4922..66dd5b754970 100644
--- a/packages/svelte/src/internal/client/proxy.js
+++ b/packages/svelte/src/internal/client/proxy.js
@@ -24,21 +24,20 @@ import { tracing_mode_flag } from '../flags/index.js';
  * @template T
  * @param {T} value
  * @param {string} [path]
- * @param {number} [path_preservation]
+ * @param {PROXY_CHANGE_PATH | PROXY_PRESERVE_PATH} path_preservation
  * @returns {T}
  */
 export function proxy(value, path, path_preservation = PROXY_PRESERVE_PATH) {
 	// if `DEV`, change the proxy `path` since we don't know if its still "owned" by its original source
 	if (
 		DEV &&
-		(path_preservation & PROXY_PRESERVE_PATH) === 0 &&
+		(path_preservation & PROXY_CHANGE_PATH) !== 0 &&
 		typeof value === 'object' &&
 		value !== null &&
 		STATE_SYMBOL in value &&
 		PROXY_PATH_SYMBOL in value
 	) {
-		value[PROXY_PATH_SYMBOL] =
-			(path_preservation & PROXY_CHANGE_PATH) === 0 ? '[$state proxy]' : path;
+		value[PROXY_PATH_SYMBOL] = path;
 	}
 	// if non-proxyable, or is already a proxy, return `value`
 	if (typeof value !== 'object' || value === null || STATE_SYMBOL in value) {

From a7a08d58603616649d3f9c88677456c23a168fe5 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Tue, 10 Jun 2025 16:00:35 -0400
Subject: [PATCH 03/12] simplify

---
 .../svelte/src/internal/client/constants.js     |  6 ------
 packages/svelte/src/internal/client/proxy.js    | 17 ++++++-----------
 2 files changed, 6 insertions(+), 17 deletions(-)

diff --git a/packages/svelte/src/internal/client/constants.js b/packages/svelte/src/internal/client/constants.js
index 268ba29c883a..98cef658bf6c 100644
--- a/packages/svelte/src/internal/client/constants.js
+++ b/packages/svelte/src/internal/client/constants.js
@@ -22,12 +22,6 @@ export const HEAD_EFFECT = 1 << 19;
 export const EFFECT_HAS_DERIVED = 1 << 20;
 export const EFFECT_IS_UPDATING = 1 << 21;
 
-// `$inspect.trace` proxy path flags
-/** Keep path the same */
-export const PROXY_PRESERVE_PATH = 1 << 1;
-/** Change proxy path to new "owner" */
-export const PROXY_CHANGE_PATH = 1 << 2;
-
 export const STATE_SYMBOL = Symbol('$state');
 export const LEGACY_PROPS = Symbol('legacy props');
 export const LOADING_ATTR_SYMBOL = Symbol('');
diff --git a/packages/svelte/src/internal/client/proxy.js b/packages/svelte/src/internal/client/proxy.js
index 66dd5b754970..cd3fbb324931 100644
--- a/packages/svelte/src/internal/client/proxy.js
+++ b/packages/svelte/src/internal/client/proxy.js
@@ -9,12 +9,7 @@ import {
 	object_prototype
 } from '../shared/utils.js';
 import { state as source, set } from './reactivity/sources.js';
-import {
-	PROXY_CHANGE_PATH,
-	PROXY_PATH_SYMBOL,
-	PROXY_PRESERVE_PATH,
-	STATE_SYMBOL
-} from '#client/constants';
+import { PROXY_PATH_SYMBOL, STATE_SYMBOL } from '#client/constants';
 import { UNINITIALIZED } from '../../constants.js';
 import * as e from './errors.js';
 import { get_stack, tag } from './dev/tracing.js';
@@ -24,14 +19,14 @@ import { tracing_mode_flag } from '../flags/index.js';
  * @template T
  * @param {T} value
  * @param {string} [path]
- * @param {PROXY_CHANGE_PATH | PROXY_PRESERVE_PATH} path_preservation
+ * @param {boolean} change_path
  * @returns {T}
  */
-export function proxy(value, path, path_preservation = PROXY_PRESERVE_PATH) {
+export function proxy(value, path, change_path = false) {
 	// if `DEV`, change the proxy `path` since we don't know if its still "owned" by its original source
 	if (
 		DEV &&
-		(path_preservation & PROXY_CHANGE_PATH) !== 0 &&
+		change_path &&
 		typeof value === 'object' &&
 		value !== null &&
 		STATE_SYMBOL in value &&
@@ -270,7 +265,7 @@ export function proxy(value, path, path_preservation = PROXY_PRESERVE_PATH) {
 					s = DEV ? tag(s, to_trace_name(prop)) : s;
 					set(
 						s,
-						with_parent(() => proxy(value, to_trace_name(prop), PROXY_CHANGE_PATH))
+						with_parent(() => proxy(value, to_trace_name(prop), true))
 					);
 					sources.set(prop, s);
 				}
@@ -278,7 +273,7 @@ export function proxy(value, path, path_preservation = PROXY_PRESERVE_PATH) {
 				has = s.v !== UNINITIALIZED;
 				set(
 					s,
-					with_parent(() => proxy(value, to_trace_name(prop), PROXY_CHANGE_PATH))
+					with_parent(() => proxy(value, to_trace_name(prop), true))
 				);
 			}
 

From 35cbd04ba54467dcb2b2247386c24dc801ff9aad Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Tue, 10 Jun 2025 16:02:07 -0400
Subject: [PATCH 04/12] tweak

---
 .../phases/3-transform/client/visitors/VariableDeclaration.js | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/VariableDeclaration.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/VariableDeclaration.js
index b531f0df6e41..f22838a3f136 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/VariableDeclaration.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/VariableDeclaration.js
@@ -89,7 +89,7 @@ export function VariableDeclaration(node, context) {
 								binding.kind === 'bindable_prop' &&
 								should_proxy(initial, context.state.scope)
 							) {
-								initial = b.call('$.proxy', initial, dev ? b.literal(id.name) : undefined);
+								initial = b.call('$.proxy', initial, dev && b.literal(id.name));
 							}
 
 							if (is_prop_source(binding, context.state)) {
@@ -132,7 +132,7 @@ export function VariableDeclaration(node, context) {
 					const is_proxy = should_proxy(value, context.state.scope);
 
 					if (rune === '$state' && is_proxy) {
-						value = b.call('$.proxy', value, dev ? b.literal(id.name) : undefined);
+						value = b.call('$.proxy', value, dev && b.literal(id.name));
 					}
 
 					if (is_state) {

From 9307ad5e111820f5e0b30b7b6913d19956e1c820 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Tue, 10 Jun 2025 16:39:08 -0400
Subject: [PATCH 05/12] tweak implementation

---
 packages/svelte/src/compiler/migrate/index.js |  2 +-
 packages/svelte/src/internal/client/proxy.js  | 65 +++++++++----------
 2 files changed, 33 insertions(+), 34 deletions(-)

diff --git a/packages/svelte/src/compiler/migrate/index.js b/packages/svelte/src/compiler/migrate/index.js
index 5ca9adb98be3..05efd22e5f47 100644
--- a/packages/svelte/src/compiler/migrate/index.js
+++ b/packages/svelte/src/compiler/migrate/index.js
@@ -18,7 +18,7 @@ import {
 import { migrate_svelte_ignore } from '../utils/extract_svelte_ignore.js';
 import { validate_component_options } from '../validate-options.js';
 import { is_reserved, is_svg, is_void } from '../../utils.js';
-import { regex_is_valid_identifier } from '../phases/patterns.js';
+import { regex_is_valid_identifier } from '../../regexes.js';
 
 const regex_style_tags = /(<style[^>]+>)([\S\s]*?)(<\/style>)/g;
 const style_placeholder = '/*$$__STYLE_CONTENT__$$*/';
diff --git a/packages/svelte/src/internal/client/proxy.js b/packages/svelte/src/internal/client/proxy.js
index cd3fbb324931..f25d940fe3d6 100644
--- a/packages/svelte/src/internal/client/proxy.js
+++ b/packages/svelte/src/internal/client/proxy.js
@@ -15,6 +15,9 @@ import * as e from './errors.js';
 import { get_stack, tag } from './dev/tracing.js';
 import { tracing_mode_flag } from '../flags/index.js';
 
+// TODO move all regexes into shared module?
+const regex_is_valid_identifier = /^[a-zA-Z_$][a-zA-Z_$0-9]*$/;
+
 /**
  * @template T
  * @param {T} value
@@ -23,17 +26,11 @@ import { tracing_mode_flag } from '../flags/index.js';
  * @returns {T}
  */
 export function proxy(value, path, change_path = false) {
-	// if `DEV`, change the proxy `path` since we don't know if its still "owned" by its original source
-	if (
-		DEV &&
-		change_path &&
-		typeof value === 'object' &&
-		value !== null &&
-		STATE_SYMBOL in value &&
-		PROXY_PATH_SYMBOL in value
-	) {
-		value[PROXY_PATH_SYMBOL] = path;
+	if (DEV && change_path) {
+		// @ts-expect-error
+		value?.[PROXY_PATH_SYMBOL]?.(path);
 	}
+
 	// if non-proxyable, or is already a proxy, return `value`
 	if (typeof value !== 'object' || value === null || STATE_SYMBOL in value) {
 		return value;
@@ -52,16 +49,6 @@ export function proxy(value, path, change_path = false) {
 
 	var stack = DEV && tracing_mode_flag ? get_stack('CreatedAt') : null;
 	var reaction = active_reaction;
-	/** @type {(prop: any) => any} */
-	var to_trace_name = DEV
-		? (prop) => {
-				return typeof prop === 'symbol'
-					? `${path}[Symbol(${prop.description ?? ''})]`
-					: typeof prop === 'number' || Number(prop) === Number(prop)
-						? `${path}[${prop}]`
-						: `${path}.${prop}`;
-			}
-		: (prop) => undefined;
 
 	/**
 	 * @template T
@@ -85,6 +72,28 @@ export function proxy(value, path, change_path = false) {
 		sources.set('length', DEV ? tag(length_source, to_trace_name('length')) : length_source);
 	}
 
+	/** @param {string | symbol} prop */
+	function to_trace_name(prop) {
+		if (typeof prop === 'symbol') return `${path}[Symbol(${prop.description ?? ''})]`;
+		if (regex_is_valid_identifier.test(prop)) return `${path}.${prop}`;
+		return /^\d+$/.test(prop) ? `${path}[${prop}]` : `${path}['${prop}']`;
+	}
+
+	/** @param {string} new_path */
+	function update_path(new_path) {
+		path = new_path;
+
+		tag(version, `${path} version`);
+
+		// rename all child sources and child proxies
+		for (const [prop, source] of sources) {
+			var label = to_trace_name(prop);
+
+			tag(source, label);
+			source.v?.[PROXY_PATH_SYMBOL]?.(label);
+		}
+	}
+
 	return new Proxy(/** @type {any} */ (value), {
 		defineProperty(_, prop, descriptor) {
 			if (
@@ -147,8 +156,9 @@ export function proxy(value, path, change_path = false) {
 			if (prop === STATE_SYMBOL) {
 				return value;
 			}
+
 			if (DEV && prop === PROXY_PATH_SYMBOL) {
-				return path;
+				return update_path;
 			}
 
 			var s = sources.get(prop);
@@ -195,7 +205,7 @@ export function proxy(value, path, change_path = false) {
 		},
 
 		has(target, prop) {
-			if (prop === STATE_SYMBOL || (DEV && prop === PROXY_PATH_SYMBOL)) {
+			if (prop === STATE_SYMBOL) {
 				return true;
 			}
 
@@ -224,17 +234,6 @@ export function proxy(value, path, change_path = false) {
 		},
 
 		set(target, prop, value, receiver) {
-			if (DEV && prop === PROXY_PATH_SYMBOL) {
-				path = value;
-				tag(version, `${path} version`);
-				// rename all child sources and child proxies
-				for (const [prop, source] of sources) {
-					tag(source, to_trace_name(prop));
-					if (typeof source.v === 'object' && source.v !== null && PROXY_PATH_SYMBOL in source.v) {
-						source.v[PROXY_PATH_SYMBOL] = to_trace_name(prop);
-					}
-				}
-			}
 			var s = sources.get(prop);
 			var has = prop in target;
 

From 016f02b721509b4c2a74384cb503b0717bb57a5e Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Tue, 10 Jun 2025 16:42:58 -0400
Subject: [PATCH 06/12] tweak implementation

---
 packages/svelte/src/internal/client/proxy.js | 35 +++++++++++---------
 1 file changed, 19 insertions(+), 16 deletions(-)

diff --git a/packages/svelte/src/internal/client/proxy.js b/packages/svelte/src/internal/client/proxy.js
index f25d940fe3d6..a9d2eedc1c97 100644
--- a/packages/svelte/src/internal/client/proxy.js
+++ b/packages/svelte/src/internal/client/proxy.js
@@ -22,15 +22,9 @@ const regex_is_valid_identifier = /^[a-zA-Z_$][a-zA-Z_$0-9]*$/;
  * @template T
  * @param {T} value
  * @param {string} [path]
- * @param {boolean} change_path
  * @returns {T}
  */
-export function proxy(value, path, change_path = false) {
-	if (DEV && change_path) {
-		// @ts-expect-error
-		value?.[PROXY_PATH_SYMBOL]?.(path);
-	}
-
+export function proxy(value, path) {
 	// if non-proxyable, or is already a proxy, return `value`
 	if (typeof value !== 'object' || value === null || STATE_SYMBOL in value) {
 		return value;
@@ -261,19 +255,28 @@ export function proxy(value, path, change_path = false) {
 			if (s === undefined) {
 				if (!has || get_descriptor(target, prop)?.writable) {
 					s = with_parent(() => source(undefined, stack));
-					s = DEV ? tag(s, to_trace_name(prop)) : s;
-					set(
-						s,
-						with_parent(() => proxy(value, to_trace_name(prop), true))
-					);
+					var p = with_parent(() => proxy(value, to_trace_name(prop)));
+
+					if (DEV) {
+						var label = to_trace_name(prop);
+						tag(s, label);
+						p?.[PROXY_PATH_SYMBOL]?.(label);
+					}
+
+					set(s, p);
 					sources.set(prop, s);
 				}
 			} else {
 				has = s.v !== UNINITIALIZED;
-				set(
-					s,
-					with_parent(() => proxy(value, to_trace_name(prop), true))
-				);
+
+				p = with_parent(() => proxy(value, to_trace_name(prop)));
+
+				if (DEV) {
+					label = to_trace_name(prop);
+					p?.[PROXY_PATH_SYMBOL]?.(label);
+				}
+
+				set(s, p);
 			}
 
 			var descriptor = Reflect.getOwnPropertyDescriptor(target, prop);

From 7f4debebcfbce0df3646a3609d9d91419d5149d9 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Tue, 10 Jun 2025 17:06:18 -0400
Subject: [PATCH 07/12] tweak implementation

---
 packages/svelte/src/compiler/migrate/index.js |  2 +-
 .../client/visitors/VariableDeclaration.js    | 12 ++-
 .../svelte/src/internal/client/dev/tracing.js | 12 ++-
 packages/svelte/src/internal/client/index.js  |  2 +-
 packages/svelte/src/internal/client/proxy.js  | 79 +++++++++++++------
 5 files changed, 76 insertions(+), 31 deletions(-)

diff --git a/packages/svelte/src/compiler/migrate/index.js b/packages/svelte/src/compiler/migrate/index.js
index 05efd22e5f47..5ca9adb98be3 100644
--- a/packages/svelte/src/compiler/migrate/index.js
+++ b/packages/svelte/src/compiler/migrate/index.js
@@ -18,7 +18,7 @@ import {
 import { migrate_svelte_ignore } from '../utils/extract_svelte_ignore.js';
 import { validate_component_options } from '../validate-options.js';
 import { is_reserved, is_svg, is_void } from '../../utils.js';
-import { regex_is_valid_identifier } from '../../regexes.js';
+import { regex_is_valid_identifier } from '../phases/patterns.js';
 
 const regex_style_tags = /(<style[^>]+>)([\S\s]*?)(<\/style>)/g;
 const style_placeholder = '/*$$__STYLE_CONTENT__$$*/';
diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/VariableDeclaration.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/VariableDeclaration.js
index f22838a3f136..da3e164ad86f 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/VariableDeclaration.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/VariableDeclaration.js
@@ -89,7 +89,11 @@ export function VariableDeclaration(node, context) {
 								binding.kind === 'bindable_prop' &&
 								should_proxy(initial, context.state.scope)
 							) {
-								initial = b.call('$.proxy', initial, dev && b.literal(id.name));
+								initial = b.call('$.proxy', initial);
+
+								if (dev) {
+									initial = b.call('$.tag_proxy', initial, b.literal(id.name));
+								}
 							}
 
 							if (is_prop_source(binding, context.state)) {
@@ -132,7 +136,11 @@ export function VariableDeclaration(node, context) {
 					const is_proxy = should_proxy(value, context.state.scope);
 
 					if (rune === '$state' && is_proxy) {
-						value = b.call('$.proxy', value, dev && b.literal(id.name));
+						value = b.call('$.proxy', value);
+
+						if (dev) {
+							value = b.call('$.tag_proxy', value, b.literal(id.name));
+						}
 					}
 
 					if (is_state) {
diff --git a/packages/svelte/src/internal/client/dev/tracing.js b/packages/svelte/src/internal/client/dev/tracing.js
index e424ebed6a30..1506b023b182 100644
--- a/packages/svelte/src/internal/client/dev/tracing.js
+++ b/packages/svelte/src/internal/client/dev/tracing.js
@@ -2,7 +2,7 @@
 import { UNINITIALIZED } from '../../../constants.js';
 import { snapshot } from '../../shared/clone.js';
 import { define_property } from '../../shared/utils.js';
-import { DERIVED, STATE_SYMBOL } from '#client/constants';
+import { DERIVED, PROXY_PATH_SYMBOL, STATE_SYMBOL } from '#client/constants';
 import { effect_tracking } from '../reactivity/effects.js';
 import { active_reaction, captured_signals, set_captured_signals, untrack } from '../runtime.js';
 
@@ -190,6 +190,16 @@ export function tag(source, name) {
 	return source;
 }
 
+/**
+ * @param {unknown} value
+ * @param {string} label
+ */
+export function tag_proxy(value, label) {
+	// @ts-expect-error
+	value?.[PROXY_PATH_SYMBOL]?.(label);
+	return value;
+}
+
 /**
  * @param {unknown} value
  */
diff --git a/packages/svelte/src/internal/client/index.js b/packages/svelte/src/internal/client/index.js
index 8e4d36d44d5f..60f9af912060 100644
--- a/packages/svelte/src/internal/client/index.js
+++ b/packages/svelte/src/internal/client/index.js
@@ -7,7 +7,7 @@ export { add_locations } from './dev/elements.js';
 export { hmr } from './dev/hmr.js';
 export { create_ownership_validator } from './dev/ownership.js';
 export { check_target, legacy_api } from './dev/legacy.js';
-export { trace, tag } from './dev/tracing.js';
+export { trace, tag, tag_proxy } from './dev/tracing.js';
 export { inspect } from './dev/inspect.js';
 export { validate_snippet_args } from './dev/validation.js';
 export { await_block as await } from './dom/blocks/await.js';
diff --git a/packages/svelte/src/internal/client/proxy.js b/packages/svelte/src/internal/client/proxy.js
index a9d2eedc1c97..bf4340ce30c4 100644
--- a/packages/svelte/src/internal/client/proxy.js
+++ b/packages/svelte/src/internal/client/proxy.js
@@ -12,7 +12,7 @@ import { state as source, set } from './reactivity/sources.js';
 import { PROXY_PATH_SYMBOL, STATE_SYMBOL } from '#client/constants';
 import { UNINITIALIZED } from '../../constants.js';
 import * as e from './errors.js';
-import { get_stack, tag } from './dev/tracing.js';
+import { get_stack, tag, tag_proxy } from './dev/tracing.js';
 import { tracing_mode_flag } from '../flags/index.js';
 
 // TODO move all regexes into shared module?
@@ -21,10 +21,9 @@ const regex_is_valid_identifier = /^[a-zA-Z_$][a-zA-Z_$0-9]*$/;
 /**
  * @template T
  * @param {T} value
- * @param {string} [path]
  * @returns {T}
  */
-export function proxy(value, path) {
+export function proxy(value) {
 	// if non-proxyable, or is already a proxy, return `value`
 	if (typeof value !== 'object' || value === null || STATE_SYMBOL in value) {
 		return value;
@@ -39,7 +38,7 @@ export function proxy(value, path) {
 	/** @type {Map<any, Source<any>>} */
 	var sources = new Map();
 	var is_proxied_array = is_array(value);
-	var version = DEV ? tag(source(0), `${path} version`) : source(0);
+	var version = source(0);
 
 	var stack = DEV && tracing_mode_flag ? get_stack('CreatedAt') : null;
 	var reaction = active_reaction;
@@ -62,10 +61,12 @@ export function proxy(value, path) {
 	if (is_proxied_array) {
 		// We need to create the length source eagerly to ensure that
 		// mutations to the array are properly synced with our proxy
-		const length_source = source(/** @type {any[]} */ (value).length, stack);
-		sources.set('length', DEV ? tag(length_source, to_trace_name('length')) : length_source);
+		sources.set('length', source(/** @type {any[]} */ (value).length, stack));
 	}
 
+	/** Used in dev for $inspect.trace() */
+	var path = '';
+
 	/** @param {string | symbol} prop */
 	function to_trace_name(prop) {
 		if (typeof prop === 'symbol') return `${path}[Symbol(${prop.description ?? ''})]`;
@@ -84,7 +85,7 @@ export function proxy(value, path) {
 			var label = to_trace_name(prop);
 
 			tag(source, label);
-			source.v?.[PROXY_PATH_SYMBOL]?.(label);
+			tag_proxy(source.v, label);
 		}
 	}
 
@@ -107,13 +108,18 @@ export function proxy(value, path) {
 
 			if (s === undefined) {
 				s = with_parent(() => source(descriptor.value, stack));
-				s = DEV && typeof prop === 'string' ? tag(s, to_trace_name(prop)) : s;
 				sources.set(prop, s);
+
+				if (DEV && typeof prop === 'string') {
+					tag(s, to_trace_name(prop));
+				}
 			} else {
-				set(
-					s,
-					with_parent(() => proxy(descriptor.value, to_trace_name(prop)))
-				);
+				var p = with_parent(() => proxy(descriptor.value));
+				set(s, p);
+
+				if (DEV) {
+					tag_proxy(p, to_trace_name(prop));
+				}
 			}
 
 			return true;
@@ -125,8 +131,12 @@ export function proxy(value, path) {
 			if (s === undefined) {
 				if (prop in target) {
 					const s = with_parent(() => source(UNINITIALIZED, stack));
-					sources.set(prop, DEV ? tag(s, to_trace_name(prop)) : s);
+					sources.set(prop, s);
 					update_version(version);
+
+					if (DEV) {
+						tag(s, to_trace_name(prop));
+					}
 				}
 			} else {
 				// When working with arrays, we need to also ensure we update the length when removing
@@ -160,10 +170,19 @@ export function proxy(value, path) {
 
 			// create a source, but only if it's an own property and not a prototype property
 			if (s === undefined && (!exists || get_descriptor(target, prop)?.writable)) {
-				s = with_parent(() =>
-					source(proxy(exists ? target[prop] : UNINITIALIZED, to_trace_name(prop)), stack)
-				);
-				s = DEV ? tag(s, to_trace_name(prop)) : s;
+				s = with_parent(() => {
+					var p = proxy(exists ? target[prop] : UNINITIALIZED);
+					var s = source(p, stack);
+
+					if (DEV) {
+						var label = to_trace_name(prop);
+						tag(s, label);
+						tag_proxy(p, label);
+					}
+
+					return s;
+				});
+
 				sources.set(prop, s);
 			}
 
@@ -211,10 +230,19 @@ export function proxy(value, path) {
 				(active_effect !== null && (!has || get_descriptor(target, prop)?.writable))
 			) {
 				if (s === undefined) {
-					s = with_parent(() =>
-						source(has ? proxy(target[prop], to_trace_name(prop)) : UNINITIALIZED, stack)
-					);
-					s = DEV ? tag(s, to_trace_name(prop)) : s;
+					s = with_parent(() => {
+						var p = has ? proxy(target[prop]) : UNINITIALIZED;
+						var s = source(p, stack);
+
+						if (DEV) {
+							var label = to_trace_name(prop);
+							tag(s, label);
+							tag_proxy(p, label);
+						}
+
+						return s;
+					});
+
 					sources.set(prop, s);
 				}
 
@@ -255,12 +283,12 @@ export function proxy(value, path) {
 			if (s === undefined) {
 				if (!has || get_descriptor(target, prop)?.writable) {
 					s = with_parent(() => source(undefined, stack));
-					var p = with_parent(() => proxy(value, to_trace_name(prop)));
+					var p = with_parent(() => proxy(value));
 
 					if (DEV) {
 						var label = to_trace_name(prop);
 						tag(s, label);
-						p?.[PROXY_PATH_SYMBOL]?.(label);
+						tag_proxy(p, label);
 					}
 
 					set(s, p);
@@ -269,11 +297,10 @@ export function proxy(value, path) {
 			} else {
 				has = s.v !== UNINITIALIZED;
 
-				p = with_parent(() => proxy(value, to_trace_name(prop)));
+				p = with_parent(() => proxy(value));
 
 				if (DEV) {
-					label = to_trace_name(prop);
-					p?.[PROXY_PATH_SYMBOL]?.(label);
+					tag_proxy(p, to_trace_name(prop));
 				}
 
 				set(s, p);

From 1d6451223aafffa903d7e71b87e16560ff7457f0 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Tue, 10 Jun 2025 17:10:13 -0400
Subject: [PATCH 08/12] hoist

---
 packages/svelte/src/internal/client/proxy.js | 38 +++++++++++---------
 1 file changed, 22 insertions(+), 16 deletions(-)

diff --git a/packages/svelte/src/internal/client/proxy.js b/packages/svelte/src/internal/client/proxy.js
index bf4340ce30c4..d529ff9a15d4 100644
--- a/packages/svelte/src/internal/client/proxy.js
+++ b/packages/svelte/src/internal/client/proxy.js
@@ -67,13 +67,6 @@ export function proxy(value) {
 	/** Used in dev for $inspect.trace() */
 	var path = '';
 
-	/** @param {string | symbol} prop */
-	function to_trace_name(prop) {
-		if (typeof prop === 'symbol') return `${path}[Symbol(${prop.description ?? ''})]`;
-		if (regex_is_valid_identifier.test(prop)) return `${path}.${prop}`;
-		return /^\d+$/.test(prop) ? `${path}[${prop}]` : `${path}['${prop}']`;
-	}
-
 	/** @param {string} new_path */
 	function update_path(new_path) {
 		path = new_path;
@@ -82,7 +75,7 @@ export function proxy(value) {
 
 		// rename all child sources and child proxies
 		for (const [prop, source] of sources) {
-			var label = to_trace_name(prop);
+			var label = get_label(path, prop);
 
 			tag(source, label);
 			tag_proxy(source.v, label);
@@ -111,14 +104,14 @@ export function proxy(value) {
 				sources.set(prop, s);
 
 				if (DEV && typeof prop === 'string') {
-					tag(s, to_trace_name(prop));
+					tag(s, get_label(path, prop));
 				}
 			} else {
 				var p = with_parent(() => proxy(descriptor.value));
 				set(s, p);
 
 				if (DEV) {
-					tag_proxy(p, to_trace_name(prop));
+					tag_proxy(p, get_label(path, prop));
 				}
 			}
 
@@ -135,7 +128,7 @@ export function proxy(value) {
 					update_version(version);
 
 					if (DEV) {
-						tag(s, to_trace_name(prop));
+						tag(s, get_label(path, prop));
 					}
 				}
 			} else {
@@ -175,7 +168,7 @@ export function proxy(value) {
 					var s = source(p, stack);
 
 					if (DEV) {
-						var label = to_trace_name(prop);
+						var label = get_label(path, prop);
 						tag(s, label);
 						tag_proxy(p, label);
 					}
@@ -235,7 +228,7 @@ export function proxy(value) {
 						var s = source(p, stack);
 
 						if (DEV) {
-							var label = to_trace_name(prop);
+							var label = get_label(path, prop);
 							tag(s, label);
 							tag_proxy(p, label);
 						}
@@ -270,8 +263,11 @@ export function proxy(value) {
 						// else a later read of the property would result in a source being created with
 						// the value of the original item at that index.
 						other_s = with_parent(() => source(UNINITIALIZED, stack));
-						other_s = DEV ? tag(other_s, to_trace_name(i)) : other_s;
 						sources.set(i + '', other_s);
+
+						if (DEV) {
+							tag(other_s, get_label(path, i));
+						}
 					}
 				}
 			}
@@ -286,7 +282,7 @@ export function proxy(value) {
 					var p = with_parent(() => proxy(value));
 
 					if (DEV) {
-						var label = to_trace_name(prop);
+						var label = get_label(path, prop);
 						tag(s, label);
 						tag_proxy(p, label);
 					}
@@ -300,7 +296,7 @@ export function proxy(value) {
 				p = with_parent(() => proxy(value));
 
 				if (DEV) {
-					tag_proxy(p, to_trace_name(prop));
+					tag_proxy(p, get_label(path, prop));
 				}
 
 				set(s, p);
@@ -356,6 +352,16 @@ export function proxy(value) {
 	});
 }
 
+/**
+ * @param {string} path
+ * @param {string | symbol} prop
+ */
+function get_label(path, prop) {
+	if (typeof prop === 'symbol') return `${path}[Symbol(${prop.description ?? ''})]`;
+	if (regex_is_valid_identifier.test(prop)) return `${path}.${prop}`;
+	return /^\d+$/.test(prop) ? `${path}[${prop}]` : `${path}['${prop}']`;
+}
+
 /**
  * @param {Source<number>} signal
  * @param {1 | -1} [d]

From 4e6e8a45906d09df3c6857b3d45caaf71ae76ef6 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Tue, 10 Jun 2025 17:13:53 -0400
Subject: [PATCH 09/12] tweak

---
 packages/svelte/src/internal/client/dev/tracing.js        | 8 ++++----
 packages/svelte/src/internal/client/reactivity/sources.js | 2 +-
 packages/svelte/src/internal/client/reactivity/types.d.ts | 2 +-
 3 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/packages/svelte/src/internal/client/dev/tracing.js b/packages/svelte/src/internal/client/dev/tracing.js
index 1506b023b182..df54a135d08e 100644
--- a/packages/svelte/src/internal/client/dev/tracing.js
+++ b/packages/svelte/src/internal/client/dev/tracing.js
@@ -43,7 +43,7 @@ function log_entry(signal, entry) {
 	const type = (signal.f & DERIVED) !== 0 ? '$derived' : '$state';
 	const current_reaction = /** @type {Reaction} */ (active_reaction);
 	const dirty = signal.wv > current_reaction.wv || current_reaction.wv === 0;
-	const { trace_name: name } = signal;
+	const { label: name } = signal;
 	const style = dirty
 		? 'color: CornflowerBlue; font-weight: bold'
 		: 'color: grey; font-weight: normal';
@@ -183,10 +183,10 @@ export function get_stack(label) {
 
 /**
  * @param {Value} source
- * @param {string} name
+ * @param {string} label
  */
-export function tag(source, name) {
-	source.trace_name = name;
+export function tag(source, label) {
+	source.label = label;
 	return source;
 }
 
diff --git a/packages/svelte/src/internal/client/reactivity/sources.js b/packages/svelte/src/internal/client/reactivity/sources.js
index ad5ad3383d14..de6c836db696 100644
--- a/packages/svelte/src/internal/client/reactivity/sources.js
+++ b/packages/svelte/src/internal/client/reactivity/sources.js
@@ -139,7 +139,7 @@ export function set(source, value, should_proxy = false) {
 		e.state_unsafe_mutation();
 	}
 
-	let new_value = should_proxy ? proxy(value, DEV ? source.trace_name : undefined) : value;
+	let new_value = should_proxy ? proxy(value, DEV ? source.label : undefined) : value;
 
 	return internal_set(source, new_value);
 }
diff --git a/packages/svelte/src/internal/client/reactivity/types.d.ts b/packages/svelte/src/internal/client/reactivity/types.d.ts
index 74982cac9192..c445ade8468d 100644
--- a/packages/svelte/src/internal/client/reactivity/types.d.ts
+++ b/packages/svelte/src/internal/client/reactivity/types.d.ts
@@ -21,7 +21,7 @@ export interface Value<V = unknown> extends Signal {
 	updated?: Error | null;
 	trace_need_increase?: boolean;
 	trace_v?: V;
-	trace_name?: string;
+	label?: string;
 	debug?: null | (() => void);
 }
 

From d2487f81b5da760603ca2a7920cbd2eef6c354e8 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Tue, 10 Jun 2025 17:15:34 -0400
Subject: [PATCH 10/12] fix

---
 packages/svelte/src/internal/client/reactivity/sources.js | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/packages/svelte/src/internal/client/reactivity/sources.js b/packages/svelte/src/internal/client/reactivity/sources.js
index de6c836db696..68d72f168640 100644
--- a/packages/svelte/src/internal/client/reactivity/sources.js
+++ b/packages/svelte/src/internal/client/reactivity/sources.js
@@ -31,7 +31,7 @@ import {
 } from '#client/constants';
 import * as e from '../errors.js';
 import { legacy_mode_flag, tracing_mode_flag } from '../../flags/index.js';
-import { get_stack } from '../dev/tracing.js';
+import { get_stack, tag_proxy } from '../dev/tracing.js';
 import { component_context, is_runes } from '../context.js';
 import { proxy } from '../proxy.js';
 import { execute_derived } from './deriveds.js';
@@ -139,7 +139,11 @@ export function set(source, value, should_proxy = false) {
 		e.state_unsafe_mutation();
 	}
 
-	let new_value = should_proxy ? proxy(value, DEV ? source.label : undefined) : value;
+	let new_value = should_proxy ? proxy(value) : value;
+
+	if (DEV && should_proxy) {
+		tag_proxy(new_value, /** @type {string} */ (source.label));
+	}
 
 	return internal_set(source, new_value);
 }

From b1f761c197f3007426affff45d1173660880cec6 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Tue, 10 Jun 2025 17:30:13 -0400
Subject: [PATCH 11/12] WIP (reduce number of with_parent calls, move towards
 possibility of combining tag and tag_proxy)

---
 packages/svelte/src/internal/client/proxy.js | 37 ++++++++++----------
 1 file changed, 18 insertions(+), 19 deletions(-)

diff --git a/packages/svelte/src/internal/client/proxy.js b/packages/svelte/src/internal/client/proxy.js
index d529ff9a15d4..e6164f46cfb6 100644
--- a/packages/svelte/src/internal/client/proxy.js
+++ b/packages/svelte/src/internal/client/proxy.js
@@ -97,23 +97,20 @@ export function proxy(value) {
 				e.state_descriptors_fixed();
 			}
 
-			var s = sources.get(prop);
-
-			if (s === undefined) {
-				s = with_parent(() => source(descriptor.value, stack));
-				sources.set(prop, s);
+			with_parent(() => {
+				var s = sources.get(prop);
 
-				if (DEV && typeof prop === 'string') {
-					tag(s, get_label(path, prop));
-				}
-			} else {
-				var p = with_parent(() => proxy(descriptor.value));
-				set(s, p);
+				if (s === undefined) {
+					s = source(descriptor.value, stack);
+					sources.set(prop, s);
 
-				if (DEV) {
-					tag_proxy(p, get_label(path, prop));
+					if (DEV && typeof prop === 'string') {
+						tag(s, get_label(path, prop));
+					}
+				} else {
+					set(s, descriptor.value, true);
 				}
-			}
+			});
 
 			return true;
 		},
@@ -278,22 +275,24 @@ export function proxy(value) {
 			// object property before writing to that property.
 			if (s === undefined) {
 				if (!has || get_descriptor(target, prop)?.writable) {
-					s = with_parent(() => source(undefined, stack));
-					var p = with_parent(() => proxy(value));
+					s = with_parent(() => {
+						var s = source(undefined, stack);
+						set(s, proxy(value));
+						return s;
+					});
 
 					if (DEV) {
 						var label = get_label(path, prop);
 						tag(s, label);
-						tag_proxy(p, label);
+						tag_proxy(s.v, label);
 					}
 
-					set(s, p);
 					sources.set(prop, s);
 				}
 			} else {
 				has = s.v !== UNINITIALIZED;
 
-				p = with_parent(() => proxy(value));
+				var p = with_parent(() => proxy(value));
 
 				if (DEV) {
 					tag_proxy(p, get_label(path, prop));

From 4105d055f9e3d578a904bf7569c5cafc175dd021 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Tue, 10 Jun 2025 18:07:19 -0400
Subject: [PATCH 12/12] DRY out

---
 .../client/visitors/VariableDeclaration.js    |  2 +-
 .../svelte/src/internal/client/dev/tracing.js |  2 ++
 packages/svelte/src/internal/client/proxy.js  | 28 +++++--------------
 .../src/internal/client/reactivity/sources.js |  2 +-
 4 files changed, 11 insertions(+), 23 deletions(-)

diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/VariableDeclaration.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/VariableDeclaration.js
index da3e164ad86f..53f18d42e43a 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/VariableDeclaration.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/VariableDeclaration.js
@@ -138,7 +138,7 @@ export function VariableDeclaration(node, context) {
 					if (rune === '$state' && is_proxy) {
 						value = b.call('$.proxy', value);
 
-						if (dev) {
+						if (dev && !is_state) {
 							value = b.call('$.tag_proxy', value, b.literal(id.name));
 						}
 					}
diff --git a/packages/svelte/src/internal/client/dev/tracing.js b/packages/svelte/src/internal/client/dev/tracing.js
index df54a135d08e..708c69e19a01 100644
--- a/packages/svelte/src/internal/client/dev/tracing.js
+++ b/packages/svelte/src/internal/client/dev/tracing.js
@@ -187,6 +187,8 @@ export function get_stack(label) {
  */
 export function tag(source, label) {
 	source.label = label;
+	tag_proxy(source.v, label);
+
 	return source;
 }
 
diff --git a/packages/svelte/src/internal/client/proxy.js b/packages/svelte/src/internal/client/proxy.js
index e6164f46cfb6..487050669933 100644
--- a/packages/svelte/src/internal/client/proxy.js
+++ b/packages/svelte/src/internal/client/proxy.js
@@ -12,7 +12,7 @@ import { state as source, set } from './reactivity/sources.js';
 import { PROXY_PATH_SYMBOL, STATE_SYMBOL } from '#client/constants';
 import { UNINITIALIZED } from '../../constants.js';
 import * as e from './errors.js';
-import { get_stack, tag, tag_proxy } from './dev/tracing.js';
+import { get_stack, tag } from './dev/tracing.js';
 import { tracing_mode_flag } from '../flags/index.js';
 
 // TODO move all regexes into shared module?
@@ -75,10 +75,7 @@ export function proxy(value) {
 
 		// rename all child sources and child proxies
 		for (const [prop, source] of sources) {
-			var label = get_label(path, prop);
-
-			tag(source, label);
-			tag_proxy(source.v, label);
+			tag(source, get_label(path, prop));
 		}
 	}
 
@@ -165,9 +162,7 @@ export function proxy(value) {
 					var s = source(p, stack);
 
 					if (DEV) {
-						var label = get_label(path, prop);
-						tag(s, label);
-						tag_proxy(p, label);
+						tag(s, get_label(path, prop));
 					}
 
 					return s;
@@ -225,9 +220,7 @@ export function proxy(value) {
 						var s = source(p, stack);
 
 						if (DEV) {
-							var label = get_label(path, prop);
-							tag(s, label);
-							tag_proxy(p, label);
+							tag(s, get_label(path, prop));
 						}
 
 						return s;
@@ -281,23 +274,16 @@ export function proxy(value) {
 						return s;
 					});
 
+					sources.set(prop, s);
+
 					if (DEV) {
-						var label = get_label(path, prop);
-						tag(s, label);
-						tag_proxy(s.v, label);
+						tag(s, get_label(path, prop));
 					}
-
-					sources.set(prop, s);
 				}
 			} else {
 				has = s.v !== UNINITIALIZED;
 
 				var p = with_parent(() => proxy(value));
-
-				if (DEV) {
-					tag_proxy(p, get_label(path, prop));
-				}
-
 				set(s, p);
 			}
 
diff --git a/packages/svelte/src/internal/client/reactivity/sources.js b/packages/svelte/src/internal/client/reactivity/sources.js
index 68d72f168640..ad7566f77218 100644
--- a/packages/svelte/src/internal/client/reactivity/sources.js
+++ b/packages/svelte/src/internal/client/reactivity/sources.js
@@ -141,7 +141,7 @@ export function set(source, value, should_proxy = false) {
 
 	let new_value = should_proxy ? proxy(value) : value;
 
-	if (DEV && should_proxy) {
+	if (DEV) {
 		tag_proxy(new_value, /** @type {string} */ (source.label));
 	}