From fd2e7a28132825bac4131781fa445cf577bbe658 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Thu, 5 Jun 2025 18:22:33 -0400
Subject: [PATCH 01/29] remove unused handle_error arguments

---
 .../src/internal/client/dom/blocks/boundary.js |  2 +-
 packages/svelte/src/internal/client/runtime.js | 18 +++++++++---------
 2 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/packages/svelte/src/internal/client/dom/blocks/boundary.js b/packages/svelte/src/internal/client/dom/blocks/boundary.js
index 53060017b935..2e94a8680642 100644
--- a/packages/svelte/src/internal/client/dom/blocks/boundary.js
+++ b/packages/svelte/src/internal/client/dom/blocks/boundary.js
@@ -109,7 +109,7 @@ export function boundary(node, props, boundary_fn) {
 								);
 							});
 						} catch (error) {
-							handle_error(error, boundary, null, boundary.ctx);
+							handle_error(error, boundary);
 						}
 
 						reset_is_throwing_error();
diff --git a/packages/svelte/src/internal/client/runtime.js b/packages/svelte/src/internal/client/runtime.js
index d790c0ad145a..2324c725931e 100644
--- a/packages/svelte/src/internal/client/runtime.js
+++ b/packages/svelte/src/internal/client/runtime.js
@@ -271,10 +271,11 @@ export function reset_is_throwing_error() {
 /**
  * @param {unknown} error
  * @param {Effect} effect
- * @param {Effect | null} previous_effect
- * @param {ComponentContext | null} component_context
+ * @param {Effect | null} [previous_effect]
  */
-export function handle_error(error, effect, previous_effect, component_context) {
+export function handle_error(error, effect, previous_effect = null) {
+	var component_context = effect.ctx;
+
 	if (is_throwing_error) {
 		if (previous_effect === null) {
 			is_throwing_error = false;
@@ -558,7 +559,6 @@ export function update_effect(effect) {
 	set_signal_status(effect, CLEAN);
 
 	var previous_effect = active_effect;
-	var previous_component_context = component_context;
 	var was_updating_effect = is_updating_effect;
 
 	active_effect = effect;
@@ -602,7 +602,7 @@ export function update_effect(effect) {
 			dev_effect_stack.push(effect);
 		}
 	} catch (error) {
-		handle_error(error, effect, previous_effect, previous_component_context || effect.ctx);
+		handle_error(error, effect, previous_effect);
 	} finally {
 		is_updating_effect = was_updating_effect;
 		active_effect = previous_effect;
@@ -637,14 +637,14 @@ function infinite_loop_guard() {
 		if (last_scheduled_effect !== null) {
 			if (DEV) {
 				try {
-					handle_error(error, last_scheduled_effect, null, null);
+					handle_error(error, last_scheduled_effect);
 				} catch (e) {
 					// Only log the effect stack if the error is re-thrown
 					log_effect_stack();
 					throw e;
 				}
 			} else {
-				handle_error(error, last_scheduled_effect, null, null);
+				handle_error(error, last_scheduled_effect);
 			}
 		} else {
 			if (DEV) {
@@ -721,7 +721,7 @@ function flush_queued_effects(effects) {
 					}
 				}
 			} catch (error) {
-				handle_error(error, effect, null, effect.ctx);
+				handle_error(error, effect);
 			}
 		}
 	}
@@ -785,7 +785,7 @@ function process_effects(root) {
 						update_effect(effect);
 					}
 				} catch (error) {
-					handle_error(error, effect, null, effect.ctx);
+					handle_error(error, effect);
 				}
 			}
 

From c0cdc5a6a32b1c5a1ff48a555ee153a0511c1454 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Thu, 5 Jun 2025 18:38:13 -0400
Subject: [PATCH 02/29] move error handling code into separate module

---
 .../internal/client/dom/blocks/boundary.js    |   5 +-
 .../src/internal/client/error-handling.js     | 138 ++++++++++++++++++
 .../svelte/src/internal/client/runtime.js     | 135 +----------------
 3 files changed, 142 insertions(+), 136 deletions(-)
 create mode 100644 packages/svelte/src/internal/client/error-handling.js

diff --git a/packages/svelte/src/internal/client/dom/blocks/boundary.js b/packages/svelte/src/internal/client/dom/blocks/boundary.js
index 2e94a8680642..0eb00bf630a7 100644
--- a/packages/svelte/src/internal/client/dom/blocks/boundary.js
+++ b/packages/svelte/src/internal/client/dom/blocks/boundary.js
@@ -2,14 +2,13 @@
 
 import { BOUNDARY_EFFECT, EFFECT_TRANSPARENT } from '#client/constants';
 import { component_context, set_component_context } from '../../context.js';
+import { handle_error, reset_is_throwing_error } from '../../error-handling.js';
 import { block, branch, destroy_effect, pause_effect } from '../../reactivity/effects.js';
 import {
 	active_effect,
 	active_reaction,
-	handle_error,
 	set_active_effect,
-	set_active_reaction,
-	reset_is_throwing_error
+	set_active_reaction
 } from '../../runtime.js';
 import {
 	hydrate_next,
diff --git a/packages/svelte/src/internal/client/error-handling.js b/packages/svelte/src/internal/client/error-handling.js
new file mode 100644
index 000000000000..3b59481b0e61
--- /dev/null
+++ b/packages/svelte/src/internal/client/error-handling.js
@@ -0,0 +1,138 @@
+/** @import { ComponentContext, Effect } from '#client' */
+import { DEV } from 'esm-env';
+import { FILENAME } from '../../constants.js';
+import { is_firefox } from './dom/operations.js';
+import { BOUNDARY_EFFECT, DESTROYED } from './constants.js';
+import { define_property } from '../shared/utils.js';
+
+// Used for DEV time error handling
+/** @param {WeakSet<Error>} value */
+const handled_errors = new WeakSet();
+
+let is_throwing_error = false;
+
+/**
+ * @param {unknown} error
+ * @param {Effect} effect
+ * @param {Effect | null} [previous_effect]
+ */
+export function handle_error(error, effect, previous_effect = null) {
+	var component_context = effect.ctx;
+
+	if (is_throwing_error) {
+		if (previous_effect === null) {
+			is_throwing_error = false;
+		}
+
+		if (should_rethrow_error(effect)) {
+			throw error;
+		}
+
+		return;
+	}
+
+	if (previous_effect !== null) {
+		is_throwing_error = true;
+	}
+
+	if (DEV && component_context !== null && error instanceof Error && !handled_errors.has(error)) {
+		handled_errors.add(error);
+
+		const component_stack = [];
+
+		const effect_name = effect.fn?.name;
+
+		if (effect_name) {
+			component_stack.push(effect_name);
+		}
+
+		/** @type {ComponentContext | null} */
+		let current_context = component_context;
+
+		while (current_context !== null) {
+			/** @type {string} */
+			var filename = current_context.function?.[FILENAME];
+
+			if (filename) {
+				const file = filename.split('/').pop();
+				component_stack.push(file);
+			}
+
+			current_context = current_context.p;
+		}
+
+		const indent = is_firefox ? '  ' : '\t';
+		define_property(error, 'message', {
+			value:
+				error.message + `\n${component_stack.map((name) => `\n${indent}in ${name}`).join('')}\n`
+		});
+		define_property(error, 'component_stack', {
+			value: component_stack
+		});
+
+		const stack = error.stack;
+
+		// Filter out internal files from callstack
+		if (stack) {
+			const lines = stack.split('\n');
+			const new_lines = [];
+			for (let i = 0; i < lines.length; i++) {
+				const line = lines[i];
+				if (line.includes('svelte/src/internal')) {
+					continue;
+				}
+				new_lines.push(line);
+			}
+			define_property(error, 'stack', {
+				value: new_lines.join('\n')
+			});
+		}
+	}
+
+	propagate_error(error, effect);
+
+	if (should_rethrow_error(effect)) {
+		throw error;
+	}
+}
+
+/**
+ * @param {unknown} error
+ * @param {Effect} effect
+ */
+function propagate_error(error, effect) {
+	/** @type {Effect | null} */
+	var current = effect;
+
+	while (current !== null) {
+		if ((current.f & BOUNDARY_EFFECT) !== 0) {
+			try {
+				// @ts-expect-error
+				current.fn(error);
+				return;
+			} catch {
+				// Remove boundary flag from effect
+				current.f ^= BOUNDARY_EFFECT;
+			}
+		}
+
+		current = current.parent;
+	}
+
+	is_throwing_error = false;
+	throw error;
+}
+
+/**
+ * @param {Effect} effect
+ */
+function should_rethrow_error(effect) {
+	return (
+		(effect.f & DESTROYED) === 0 &&
+		(effect.parent === null || (effect.parent.f & BOUNDARY_EFFECT) === 0)
+	);
+}
+
+export function reset_is_throwing_error() {
+	is_throwing_error = false;
+}
diff --git a/packages/svelte/src/internal/client/runtime.js b/packages/svelte/src/internal/client/runtime.js
index 2324c725931e..2ac3125a0f76 100644
--- a/packages/svelte/src/internal/client/runtime.js
+++ b/packages/svelte/src/internal/client/runtime.js
@@ -29,7 +29,7 @@ import { flush_tasks } from './dom/task.js';
 import { internal_set, old_values } from './reactivity/sources.js';
 import { destroy_derived_effects, update_derived } from './reactivity/deriveds.js';
 import * as e from './errors.js';
-import { FILENAME } from '../../constants.js';
+
 import { tracing_mode_flag } from '../flags/index.js';
 import { tracing_expressions, get_stack } from './dev/tracing.js';
 import {
@@ -39,12 +39,7 @@ import {
 	set_component_context,
 	set_dev_current_component_function
 } from './context.js';
-import { is_firefox } from './dom/operations.js';
-
-// Used for DEV time error handling
-/** @param {WeakSet<Error>} value */
-const handled_errors = new WeakSet();
-let is_throwing_error = false;
+import { handle_error } from './error-handling.js';
 
 let is_flushing = false;
 
@@ -227,132 +222,6 @@ export function check_dirtiness(reaction) {
 	return false;
 }
 
-/**
- * @param {unknown} error
- * @param {Effect} effect
- */
-function propagate_error(error, effect) {
-	/** @type {Effect | null} */
-	var current = effect;
-
-	while (current !== null) {
-		if ((current.f & BOUNDARY_EFFECT) !== 0) {
-			try {
-				// @ts-expect-error
-				current.fn(error);
-				return;
-			} catch {
-				// Remove boundary flag from effect
-				current.f ^= BOUNDARY_EFFECT;
-			}
-		}
-
-		current = current.parent;
-	}
-
-	is_throwing_error = false;
-	throw error;
-}
-
-/**
- * @param {Effect} effect
- */
-function should_rethrow_error(effect) {
-	return (
-		(effect.f & DESTROYED) === 0 &&
-		(effect.parent === null || (effect.parent.f & BOUNDARY_EFFECT) === 0)
-	);
-}
-
-export function reset_is_throwing_error() {
-	is_throwing_error = false;
-}
-
-/**
- * @param {unknown} error
- * @param {Effect} effect
- * @param {Effect | null} [previous_effect]
- */
-export function handle_error(error, effect, previous_effect = null) {
-	var component_context = effect.ctx;
-
-	if (is_throwing_error) {
-		if (previous_effect === null) {
-			is_throwing_error = false;
-		}
-
-		if (should_rethrow_error(effect)) {
-			throw error;
-		}
-
-		return;
-	}
-
-	if (previous_effect !== null) {
-		is_throwing_error = true;
-	}
-
-	if (DEV && component_context !== null && error instanceof Error && !handled_errors.has(error)) {
-		handled_errors.add(error);
-
-		const component_stack = [];
-
-		const effect_name = effect.fn?.name;
-
-		if (effect_name) {
-			component_stack.push(effect_name);
-		}
-
-		/** @type {ComponentContext | null} */
-		let current_context = component_context;
-
-		while (current_context !== null) {
-			/** @type {string} */
-			var filename = current_context.function?.[FILENAME];
-
-			if (filename) {
-				const file = filename.split('/').pop();
-				component_stack.push(file);
-			}
-
-			current_context = current_context.p;
-		}
-
-		const indent = is_firefox ? '  ' : '\t';
-		define_property(error, 'message', {
-			value:
-				error.message + `\n${component_stack.map((name) => `\n${indent}in ${name}`).join('')}\n`
-		});
-		define_property(error, 'component_stack', {
-			value: component_stack
-		});
-
-		const stack = error.stack;
-
-		// Filter out internal files from callstack
-		if (stack) {
-			const lines = stack.split('\n');
-			const new_lines = [];
-			for (let i = 0; i < lines.length; i++) {
-				const line = lines[i];
-				if (line.includes('svelte/src/internal')) {
-					continue;
-				}
-				new_lines.push(line);
-			}
-			define_property(error, 'stack', {
-				value: new_lines.join('\n')
-			});
-		}
-	}
-
-	propagate_error(error, effect);
-
-	if (should_rethrow_error(effect)) {
-		throw error;
-	}
-}
-
 /**
  * @param {Value} signal
  * @param {Effect} effect

From 04817caf83dc848797f6473486105d576827a7ee Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Thu, 5 Jun 2025 18:41:07 -0400
Subject: [PATCH 03/29] tidy up

---
 .../svelte/src/internal/client/error-handling.js     | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/packages/svelte/src/internal/client/error-handling.js b/packages/svelte/src/internal/client/error-handling.js
index 3b59481b0e61..90294ba5cef2 100644
--- a/packages/svelte/src/internal/client/error-handling.js
+++ b/packages/svelte/src/internal/client/error-handling.js
@@ -11,6 +11,10 @@ const handled_errors = new WeakSet();
 
 let is_throwing_error = false;
 
+export function reset_is_throwing_error() {
+	is_throwing_error = false;
+}
+
 /**
  * @param {unknown} error
  * @param {Effect} effect
@@ -89,7 +93,7 @@ export function handle_error(error, effect, previous_effect = null) {
 		}
 	}
 
-	propagate_error(error, effect);
+	invoke_error_boundary(error, effect);
 
 	if (should_rethrow_error(effect)) {
 		throw error;
@@ -100,7 +104,7 @@ export function handle_error(error, effect, previous_effect = null) {
  * @param {unknown} error
  * @param {Effect} effect
  */
-function propagate_error(error, effect) {
+function invoke_error_boundary(error, effect) {
 	/** @type {Effect | null} */
 	var current = effect;
 
@@ -132,7 +136,3 @@ function should_rethrow_error(effect) {
 		(effect.parent === null || (effect.parent.f & BOUNDARY_EFFECT) === 0)
 	);
 }
-
-export function reset_is_throwing_error() {
-	is_throwing_error = false;
-}

From f077415e43dfa41f36e62901b6717f43a0d73fac Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Thu, 5 Jun 2025 18:52:36 -0400
Subject: [PATCH 04/29] simplify

---
 .../src/internal/client/error-handling.js     | 99 ++++++++-----------
 1 file changed, 43 insertions(+), 56 deletions(-)

diff --git a/packages/svelte/src/internal/client/error-handling.js b/packages/svelte/src/internal/client/error-handling.js
index 90294ba5cef2..754267184d4c 100644
--- a/packages/svelte/src/internal/client/error-handling.js
+++ b/packages/svelte/src/internal/client/error-handling.js
@@ -1,4 +1,4 @@
-/** @import { ComponentContext, Effect } from '#client' */
+/** @import { Effect } from '#client' */
 import { DEV } from 'esm-env';
 import { FILENAME } from '../../constants.js';
 import { is_firefox } from './dom/operations.js';
@@ -7,7 +7,7 @@ import { define_property } from '../shared/utils.js';
 
 // Used for DEV time error handling
 /** @param {WeakSet<Error>} value */
-const handled_errors = new WeakSet();
+const adjusted_errors = new WeakSet();
 
 let is_throwing_error = false;
 
@@ -21,8 +21,6 @@ export function reset_is_throwing_error() {
  * @param {Effect | null} [previous_effect]
  */
 export function handle_error(error, effect, previous_effect = null) {
-	var component_context = effect.ctx;
-
 	if (is_throwing_error) {
 		if (previous_effect === null) {
 			is_throwing_error = false;
@@ -39,58 +37,8 @@ export function handle_error(error, effect, previous_effect = null) {
 		is_throwing_error = true;
 	}
 
-	if (DEV && component_context !== null && error instanceof Error && !handled_errors.has(error)) {
-		handled_errors.add(error);
-
-		const component_stack = [];
-
-		const effect_name = effect.fn?.name;
-
-		if (effect_name) {
-			component_stack.push(effect_name);
-		}
-
-		/** @type {ComponentContext | null} */
-		let current_context = component_context;
-
-		while (current_context !== null) {
-			/** @type {string} */
-			var filename = current_context.function?.[FILENAME];
-
-			if (filename) {
-				const file = filename.split('/').pop();
-				component_stack.push(file);
-			}
-
-			current_context = current_context.p;
-		}
-
-		const indent = is_firefox ? '  ' : '\t';
-		define_property(error, 'message', {
-			value:
-				error.message + `\n${component_stack.map((name) => `\n${indent}in ${name}`).join('')}\n`
-		});
-		define_property(error, 'component_stack', {
-			value: component_stack
-		});
-
-		const stack = error.stack;
-
-		// Filter out internal files from callstack
-		if (stack) {
-			const lines = stack.split('\n');
-			const new_lines = [];
-			for (let i = 0; i < lines.length; i++) {
-				const line = lines[i];
-				if (line.includes('svelte/src/internal')) {
-					continue;
-				}
-				new_lines.push(line);
-			}
-			define_property(error, 'stack', {
-				value: new_lines.join('\n')
-			});
-		}
+	if (DEV && error instanceof Error) {
+		adjust_error(error, effect);
 	}
 
 	invoke_error_boundary(error, effect);
@@ -136,3 +84,42 @@ function should_rethrow_error(effect) {
 		(effect.parent === null || (effect.parent.f & BOUNDARY_EFFECT) === 0)
 	);
 }
+
+/**
+ * Add useful information to the error message/stack
+ * @param {Error} error
+ * @param {Effect} effect
+ */
+function adjust_error(error, effect) {
+	if (adjusted_errors.has(error)) return;
+	adjusted_errors.add(error);
+
+	const component_stack = [effect.fn?.name ?? '<unknown>'];
+	const indent = is_firefox ? '  ' : '\t';
+
+	var context = effect.ctx;
+
+	while (context !== null) {
+		component_stack.push(context.function?.[FILENAME].split('/').pop());
+		context = context.p;
+	}
+
+	define_property(error, 'message', {
+		value: error.message + `\n${component_stack.map((name) => `\n${indent}in ${name}`).join('')}\n`
+	});
+
+	// TODO what is this for? can we get rid of it?
+	define_property(error, 'component_stack', {
+		value: component_stack
+	});
+
+	// Filter out internal files from callstack
+	if (error.stack) {
+		define_property(error, 'stack', {
+			value: error.stack
+				.split('\n')
+				.filter((line) => !line.includes('svelte/src/internal'))
+				.join('\n')
+		});
+	}
+}

From 7d72187fedc04aa75bc340f71831624b3186cd8b Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Thu, 5 Jun 2025 19:25:26 -0400
Subject: [PATCH 05/29] remove unnecessary handle_error invocation

---
 packages/svelte/src/internal/client/dom/blocks/boundary.js | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/packages/svelte/src/internal/client/dom/blocks/boundary.js b/packages/svelte/src/internal/client/dom/blocks/boundary.js
index 0eb00bf630a7..064c5212185a 100644
--- a/packages/svelte/src/internal/client/dom/blocks/boundary.js
+++ b/packages/svelte/src/internal/client/dom/blocks/boundary.js
@@ -2,7 +2,7 @@
 
 import { BOUNDARY_EFFECT, EFFECT_TRANSPARENT } from '#client/constants';
 import { component_context, set_component_context } from '../../context.js';
-import { handle_error, reset_is_throwing_error } from '../../error-handling.js';
+import { reset_is_throwing_error } from '../../error-handling.js';
 import { block, branch, destroy_effect, pause_effect } from '../../reactivity/effects.js';
 import {
 	active_effect,
@@ -107,8 +107,8 @@ export function boundary(node, props, boundary_fn) {
 									() => reset
 								);
 							});
-						} catch (error) {
-							handle_error(error, boundary);
+						} catch {
+							// do nothing, handle_error has already been invoked
 						}
 
 						reset_is_throwing_error();

From 34c2900a647e7ac34c2384a5875e02e8dad96654 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Thu, 5 Jun 2025 23:10:07 -0400
Subject: [PATCH 06/29] WIP

---
 .../src/internal/client/error-handling.js     | 22 ++-----
 .../svelte/src/internal/client/runtime.js     | 63 +++++++++++--------
 .../samples/error-boundary-12/_config.js      |  7 +--
 .../samples/error-boundary-12/main.svelte     | 10 ++-
 .../samples/error-boundary-13/Child.svelte    | 13 +++-
 .../samples/error-boundary-13/_config.js      |  2 +-
 .../samples/error-boundary-13/main.svelte     | 11 +---
 .../samples/error-boundary-18/_config.js      |  8 +--
 .../samples/error-boundary-18/main.svelte     | 12 ++--
 9 files changed, 72 insertions(+), 76 deletions(-)

diff --git a/packages/svelte/src/internal/client/error-handling.js b/packages/svelte/src/internal/client/error-handling.js
index 754267184d4c..ead5e0646fc5 100644
--- a/packages/svelte/src/internal/client/error-handling.js
+++ b/packages/svelte/src/internal/client/error-handling.js
@@ -15,37 +15,25 @@ export function reset_is_throwing_error() {
 	is_throwing_error = false;
 }
 
+/** @type {null | unknown} */
+let current_error = null;
+
 /**
  * @param {unknown} error
  * @param {Effect} effect
  * @param {Effect | null} [previous_effect]
  */
 export function handle_error(error, effect, previous_effect = null) {
-	if (is_throwing_error) {
-		if (previous_effect === null) {
-			is_throwing_error = false;
-		}
-
-		if (should_rethrow_error(effect)) {
-			throw error;
-		}
-
+	if (error === current_error) {
+		// TODO is this necessary?
 		return;
 	}
 
-	if (previous_effect !== null) {
-		is_throwing_error = true;
-	}
-
 	if (DEV && error instanceof Error) {
 		adjust_error(error, effect);
 	}
 
 	invoke_error_boundary(error, effect);
-
-	if (should_rethrow_error(effect)) {
-		throw error;
-	}
 }
 
 /**
diff --git a/packages/svelte/src/internal/client/runtime.js b/packages/svelte/src/internal/client/runtime.js
index 2ac3125a0f76..4eddd7d3bfff 100644
--- a/packages/svelte/src/internal/client/runtime.js
+++ b/packages/svelte/src/internal/client/runtime.js
@@ -343,6 +343,13 @@ export function update_reaction(reaction) {
 		}
 
 		return result;
+	} catch (error) {
+		var effect = get_effect(reaction);
+		if (effect) {
+			handle_error(error, effect);
+		} else {
+			throw error;
+		}
 	} finally {
 		new_deps = previous_deps;
 		skipped_deps = previous_skipped_deps;
@@ -357,6 +364,18 @@ export function update_reaction(reaction) {
 	}
 }
 
+/** @param {Reaction} reaction */
+function get_effect(reaction) {
+	/** @type {Reaction | null;} */
+	var r = reaction;
+
+	while (r !== null && (r.f & DERIVED) !== 0) {
+		r = /** @type {Derived} */ (r).parent;
+	}
+
+	return /** @type {Effect | null} */ (r);
+}
+
 /**
  * @template V
  * @param {Reaction} signal
@@ -470,8 +489,6 @@ export function update_effect(effect) {
 		if (DEV) {
 			dev_effect_stack.push(effect);
 		}
-	} catch (error) {
-		handle_error(error, effect, previous_effect);
 	} finally {
 		is_updating_effect = was_updating_effect;
 		active_effect = previous_effect;
@@ -570,27 +587,23 @@ function flush_queued_effects(effects) {
 		var effect = effects[i];
 
 		if ((effect.f & (DESTROYED | INERT)) === 0) {
-			try {
-				if (check_dirtiness(effect)) {
-					update_effect(effect);
-
-					// Effects with no dependencies or teardown do not get added to the effect tree.
-					// Deferred effects (e.g. `$effect(...)`) _are_ added to the tree because we
-					// don't know if we need to keep them until they are executed. Doing the check
-					// here (rather than in `update_effect`) allows us to skip the work for
-					// immediate effects.
-					if (effect.deps === null && effect.first === null && effect.nodes_start === null) {
-						if (effect.teardown === null) {
-							// remove this effect from the graph
-							unlink_effect(effect);
-						} else {
-							// keep the effect in the graph, but free up some memory
-							effect.fn = null;
-						}
+			if (check_dirtiness(effect)) {
+				update_effect(effect);
+
+				// Effects with no dependencies or teardown do not get added to the effect tree.
+				// Deferred effects (e.g. `$effect(...)`) _are_ added to the tree because we
+				// don't know if we need to keep them until they are executed. Doing the check
+				// here (rather than in `update_effect`) allows us to skip the work for
+				// immediate effects.
+				if (effect.deps === null && effect.first === null && effect.nodes_start === null) {
+					if (effect.teardown === null) {
+						// remove this effect from the graph
+						unlink_effect(effect);
+					} else {
+						// keep the effect in the graph, but free up some memory
+						effect.fn = null;
 					}
 				}
-			} catch (error) {
-				handle_error(error, effect);
 			}
 		}
 	}
@@ -649,12 +662,8 @@ function process_effects(root) {
 			} else if (is_branch) {
 				effect.f ^= CLEAN;
 			} else {
-				try {
-					if (check_dirtiness(effect)) {
-						update_effect(effect);
-					}
-				} catch (error) {
-					handle_error(error, effect);
+				if (check_dirtiness(effect)) {
+					update_effect(effect);
 				}
 			}
 
diff --git a/packages/svelte/tests/runtime-runes/samples/error-boundary-12/_config.js b/packages/svelte/tests/runtime-runes/samples/error-boundary-12/_config.js
index b3edfefa2002..4e771dfafa04 100644
--- a/packages/svelte/tests/runtime-runes/samples/error-boundary-12/_config.js
+++ b/packages/svelte/tests/runtime-runes/samples/error-boundary-12/_config.js
@@ -5,9 +5,8 @@ export default test({
 	test({ assert, target }) {
 		const btn = target.querySelector('button');
 
-		btn?.click();
-		flushSync();
-
-		assert.htmlEqual(target.innerHTML, `<button>change</button><p>Error occured</p>`);
+		assert.throws(() => {
+			flushSync(() => btn?.click());
+		}, /kaboom/);
 	}
 });
diff --git a/packages/svelte/tests/runtime-runes/samples/error-boundary-12/main.svelte b/packages/svelte/tests/runtime-runes/samples/error-boundary-12/main.svelte
index bae46c2590dc..d9dee1e2b037 100644
--- a/packages/svelte/tests/runtime-runes/samples/error-boundary-12/main.svelte
+++ b/packages/svelte/tests/runtime-runes/samples/error-boundary-12/main.svelte
@@ -1,20 +1,18 @@
 <script>
 	let count = $state(0);
 
-	const things = $derived.by(() => {
+	const d = $derived.by(() => {
 		if (count === 1) {
-			throw new Error('123')
+			throw new Error('kaboom')
 		}
-		return [1, 2 ,3]
+		return count
 	})
 </script>
 
 <button onclick={() => count++}>change</button>
 
 <svelte:boundary>
-	{#each things as thing}
-		<p>{thing}</p>
-	{/each}
+	{d}
 
 	{#snippet failed()}
 		<p>Error occured</p>
diff --git a/packages/svelte/tests/runtime-runes/samples/error-boundary-13/Child.svelte b/packages/svelte/tests/runtime-runes/samples/error-boundary-13/Child.svelte
index 6e607871d38f..de482da985e9 100644
--- a/packages/svelte/tests/runtime-runes/samples/error-boundary-13/Child.svelte
+++ b/packages/svelte/tests/runtime-runes/samples/error-boundary-13/Child.svelte
@@ -1,7 +1,14 @@
 <script>
-	const { things } = $props();
+	const { count } = $props();
+
+	const d = $derived.by(() => {
+		if (count === 1) {
+			throw new Error('kaboom')
+		}
+		return count
+	});
 
 	$effect(() => {
-		things
-	})
+		d;
+	});
 </script>
diff --git a/packages/svelte/tests/runtime-runes/samples/error-boundary-13/_config.js b/packages/svelte/tests/runtime-runes/samples/error-boundary-13/_config.js
index b3edfefa2002..3825dc781194 100644
--- a/packages/svelte/tests/runtime-runes/samples/error-boundary-13/_config.js
+++ b/packages/svelte/tests/runtime-runes/samples/error-boundary-13/_config.js
@@ -8,6 +8,6 @@ export default test({
 		btn?.click();
 		flushSync();
 
-		assert.htmlEqual(target.innerHTML, `<button>change</button><p>Error occured</p>`);
+		assert.htmlEqual(target.innerHTML, `<button>change</button><p>Error occurred</p>`);
 	}
 });
diff --git a/packages/svelte/tests/runtime-runes/samples/error-boundary-13/main.svelte b/packages/svelte/tests/runtime-runes/samples/error-boundary-13/main.svelte
index 65b71106fab9..56e484667597 100644
--- a/packages/svelte/tests/runtime-runes/samples/error-boundary-13/main.svelte
+++ b/packages/svelte/tests/runtime-runes/samples/error-boundary-13/main.svelte
@@ -2,21 +2,14 @@
 	import Child from './Child.svelte';
 
 	let count = $state(0);
-
-	const things = $derived.by(() => {
-		if (count === 1) {
-			throw new Error('123')
-		}
-		return [1, 2 ,3]
-	})
 </script>
 
 <button onclick={() => count++}>change</button>
 
 <svelte:boundary>
-	<Child {things} />
+	<Child {count} />
 
 	{#snippet failed()}
-		<p>Error occured</p>
+		<p>Error occurred</p>
 	{/snippet}
 </svelte:boundary>
diff --git a/packages/svelte/tests/runtime-runes/samples/error-boundary-18/_config.js b/packages/svelte/tests/runtime-runes/samples/error-boundary-18/_config.js
index fedaaa9ad11f..e092d0e7c752 100644
--- a/packages/svelte/tests/runtime-runes/samples/error-boundary-18/_config.js
+++ b/packages/svelte/tests/runtime-runes/samples/error-boundary-18/_config.js
@@ -5,11 +5,11 @@ export default test({
 	test({ assert, target }) {
 		let btn = target.querySelector('button');
 
-		btn?.click();
-		btn?.click();
-
 		assert.throws(() => {
-			flushSync();
+			flushSync(() => {
+				btn?.click();
+				btn?.click();
+			});
 		}, /test\n\n\tin {expression}\n/);
 	}
 });
diff --git a/packages/svelte/tests/runtime-runes/samples/error-boundary-18/main.svelte b/packages/svelte/tests/runtime-runes/samples/error-boundary-18/main.svelte
index b9de7126dbf7..e73dcacc8aa7 100644
--- a/packages/svelte/tests/runtime-runes/samples/error-boundary-18/main.svelte
+++ b/packages/svelte/tests/runtime-runes/samples/error-boundary-18/main.svelte
@@ -1,16 +1,18 @@
 <script>
 	let count = $state(0);
 
-	let test = $derived.by(() => {
+	function maybe_throw() {
 		if (count > 1) {
 			throw new Error('test');
 		}
-	});
+
+		return count;
+	}
 </script>
 
 <svelte:boundary onerror={(e) => { throw(e) }}>
-		<div>Count: {count}</div>
-		<button onclick={() => count++}>Increment</button>
-		{count} / {test}
+	<div>Count: {count}</div>
+	<button onclick={() => count++}>Increment</button>
+	{count} / {maybe_throw()}
 </svelte:boundary>
 

From 1d37bf1fb61926c3b7c01eada4ea06c92d3e1fc7 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Thu, 5 Jun 2025 23:34:31 -0400
Subject: [PATCH 07/29] WIP

---
 .../svelte/src/internal/client/dom/blocks/boundary.js    | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/packages/svelte/src/internal/client/dom/blocks/boundary.js b/packages/svelte/src/internal/client/dom/blocks/boundary.js
index 064c5212185a..a886c7d7919a 100644
--- a/packages/svelte/src/internal/client/dom/blocks/boundary.js
+++ b/packages/svelte/src/internal/client/dom/blocks/boundary.js
@@ -83,7 +83,14 @@ export function boundary(node, props, boundary_fn) {
 				});
 			};
 
-			onerror?.(error, reset);
+			var previous_reaction = active_reaction;
+
+			try {
+				set_active_reaction(null);
+				onerror?.(error, reset);
+			} finally {
+				set_active_reaction(previous_reaction);
+			}
 
 			if (boundary_effect) {
 				destroy_effect(boundary_effect);

From 051e0e3ebe74a409d4656f6352ee5c2104125754 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Fri, 6 Jun 2025 06:42:57 -0400
Subject: [PATCH 08/29] WIP

---
 .../src/internal/client/reactivity/effects.js | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/packages/svelte/src/internal/client/reactivity/effects.js b/packages/svelte/src/internal/client/reactivity/effects.js
index 36be1ecd0427..ca1da7f9cd79 100644
--- a/packages/svelte/src/internal/client/reactivity/effects.js
+++ b/packages/svelte/src/internal/client/reactivity/effects.js
@@ -332,16 +332,23 @@ export function render_effect(fn) {
  * @returns {Effect}
  */
 export function template_effect(fn, thunks = [], d = derived) {
-	const deriveds = thunks.map(d);
-	const effect = () => fn(...deriveds.map(get));
-
 	if (DEV) {
-		define_property(effect, 'name', {
-			value: '{expression}'
+		// wrap the effect so that we can decorate stack trace with `in {expression}`
+		// (TODO maybe there's a better approach?)
+		return render_effect(() => {
+			var outer = /** @type {Effect} */ (active_effect);
+			var inner = () => fn(...deriveds.map(get));
+
+			define_property(outer.fn, 'name', { value: '{expression}' });
+			define_property(inner, 'name', { value: '{expression}' });
+
+			const deriveds = thunks.map(d);
+			block(inner);
 		});
 	}
 
-	return block(effect);
+	const deriveds = thunks.map(d);
+	return block(() => fn(...deriveds.map(get)));
 }
 
 /**

From 682490dfd9c7923f2632ae1938b8185ab4294ae1 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Fri, 6 Jun 2025 06:43:16 -0400
Subject: [PATCH 09/29] note to self

---
 packages/svelte/src/internal/client/dom/blocks/boundary.js | 1 +
 1 file changed, 1 insertion(+)

diff --git a/packages/svelte/src/internal/client/dom/blocks/boundary.js b/packages/svelte/src/internal/client/dom/blocks/boundary.js
index a886c7d7919a..634fed0607cd 100644
--- a/packages/svelte/src/internal/client/dom/blocks/boundary.js
+++ b/packages/svelte/src/internal/client/dom/blocks/boundary.js
@@ -74,6 +74,7 @@ export function boundary(node, props, boundary_fn) {
 			}
 
 			var reset = () => {
+				// TODO does this make sense?
 				pause_effect(boundary_effect);
 
 				with_boundary(boundary, () => {

From dc7e21d18e7126b517b361f8d505f43e4921db5d Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Fri, 6 Jun 2025 08:05:43 -0400
Subject: [PATCH 10/29] WIP

---
 .../svelte/src/internal/client/error-handling.js |  2 +-
 .../src/internal/client/reactivity/effects.js    |  9 ++-------
 packages/svelte/src/internal/client/runtime.js   | 16 +++++++++++++---
 3 files changed, 16 insertions(+), 11 deletions(-)

diff --git a/packages/svelte/src/internal/client/error-handling.js b/packages/svelte/src/internal/client/error-handling.js
index ead5e0646fc5..eaca6cf390d5 100644
--- a/packages/svelte/src/internal/client/error-handling.js
+++ b/packages/svelte/src/internal/client/error-handling.js
@@ -40,7 +40,7 @@ export function handle_error(error, effect, previous_effect = null) {
  * @param {unknown} error
  * @param {Effect} effect
  */
-function invoke_error_boundary(error, effect) {
+export function invoke_error_boundary(error, effect) {
 	/** @type {Effect | null} */
 	var current = effect;
 
diff --git a/packages/svelte/src/internal/client/reactivity/effects.js b/packages/svelte/src/internal/client/reactivity/effects.js
index ca1da7f9cd79..6c7c21d7dc88 100644
--- a/packages/svelte/src/internal/client/reactivity/effects.js
+++ b/packages/svelte/src/internal/client/reactivity/effects.js
@@ -114,13 +114,8 @@ function create_effect(type, fn, sync, push = true) {
 	}
 
 	if (sync) {
-		try {
-			update_effect(effect);
-			effect.f |= EFFECT_RAN;
-		} catch (e) {
-			destroy_effect(effect);
-			throw e;
-		}
+		update_effect(effect);
+		effect.f |= EFFECT_RAN;
 	} else if (fn !== null) {
 		schedule_effect(effect);
 	}
diff --git a/packages/svelte/src/internal/client/runtime.js b/packages/svelte/src/internal/client/runtime.js
index 4eddd7d3bfff..7745f975f851 100644
--- a/packages/svelte/src/internal/client/runtime.js
+++ b/packages/svelte/src/internal/client/runtime.js
@@ -23,7 +23,8 @@ import {
 	LEGACY_DERIVED_PROP,
 	DISCONNECTED,
 	BOUNDARY_EFFECT,
-	EFFECT_IS_UPDATING
+	EFFECT_IS_UPDATING,
+	EFFECT_RAN
 } from './constants.js';
 import { flush_tasks } from './dom/task.js';
 import { internal_set, old_values } from './reactivity/sources.js';
@@ -39,7 +40,7 @@ import {
 	set_component_context,
 	set_dev_current_component_function
 } from './context.js';
-import { handle_error } from './error-handling.js';
+import { handle_error, invoke_error_boundary } from './error-handling.js';
 
 let is_flushing = false;
 
@@ -344,9 +345,18 @@ export function update_reaction(reaction) {
 
 		return result;
 	} catch (error) {
+		// TODO think we can just use active_effect here?
 		var effect = get_effect(reaction);
+
 		if (effect) {
-			handle_error(error, effect);
+			if ((effect.f & EFFECT_RAN) !== 0) {
+				invoke_error_boundary(error, effect);
+			} else if ((effect.f & BOUNDARY_EFFECT) !== 0) {
+				// invoke directly
+				effect.fn(error);
+			} else {
+				throw error;
+			}
 		} else {
 			throw error;
 		}

From dcbd613e3098cea0dd41511e3da00992085bf90e Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Fri, 6 Jun 2025 08:16:39 -0400
Subject: [PATCH 11/29] WIP

---
 packages/svelte/src/internal/client/dom/blocks/boundary.js | 6 +++---
 packages/svelte/src/internal/client/error-handling.js      | 2 +-
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/packages/svelte/src/internal/client/dom/blocks/boundary.js b/packages/svelte/src/internal/client/dom/blocks/boundary.js
index 634fed0607cd..2387b22f5198 100644
--- a/packages/svelte/src/internal/client/dom/blocks/boundary.js
+++ b/packages/svelte/src/internal/client/dom/blocks/boundary.js
@@ -2,7 +2,7 @@
 
 import { BOUNDARY_EFFECT, EFFECT_TRANSPARENT } from '#client/constants';
 import { component_context, set_component_context } from '../../context.js';
-import { reset_is_throwing_error } from '../../error-handling.js';
+import { invoke_error_boundary, reset_is_throwing_error } from '../../error-handling.js';
 import { block, branch, destroy_effect, pause_effect } from '../../reactivity/effects.js';
 import {
 	active_effect,
@@ -115,8 +115,8 @@ export function boundary(node, props, boundary_fn) {
 									() => reset
 								);
 							});
-						} catch {
-							// do nothing, handle_error has already been invoked
+						} catch (error) {
+							invoke_error_boundary(error, /** @type {Effect} */ (boundary.parent));
 						}
 
 						reset_is_throwing_error();
diff --git a/packages/svelte/src/internal/client/error-handling.js b/packages/svelte/src/internal/client/error-handling.js
index eaca6cf390d5..19f6cba2b88c 100644
--- a/packages/svelte/src/internal/client/error-handling.js
+++ b/packages/svelte/src/internal/client/error-handling.js
@@ -51,7 +51,7 @@ export function invoke_error_boundary(error, effect) {
 				current.fn(error);
 				return;
 			} catch {
-				// Remove boundary flag from effect
+				// Remove boundary flag from effect (TODO is this still useful?)
 				current.f ^= BOUNDARY_EFFECT;
 			}
 		}

From 4c33df256e4b28b7aa8603724e4d9912c40b4c8d Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Fri, 6 Jun 2025 08:25:41 -0400
Subject: [PATCH 12/29] unused

---
 packages/svelte/src/internal/client/error-handling.js | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/packages/svelte/src/internal/client/error-handling.js b/packages/svelte/src/internal/client/error-handling.js
index 19f6cba2b88c..410b1e4a80d6 100644
--- a/packages/svelte/src/internal/client/error-handling.js
+++ b/packages/svelte/src/internal/client/error-handling.js
@@ -21,9 +21,8 @@ let current_error = null;
 /**
  * @param {unknown} error
  * @param {Effect} effect
- * @param {Effect | null} [previous_effect]
  */
-export function handle_error(error, effect, previous_effect = null) {
+export function handle_error(error, effect) {
 	if (error === current_error) {
 		// TODO is this necessary?
 		return;

From 5256e491eb8c0353c664989c1b1b51e057723352 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Fri, 6 Jun 2025 08:31:22 -0400
Subject: [PATCH 13/29] WIP

---
 .../src/internal/client/error-handling.js     |  2 +-
 .../svelte/src/internal/client/runtime.js     | 25 +++++++++----------
 2 files changed, 13 insertions(+), 14 deletions(-)

diff --git a/packages/svelte/src/internal/client/error-handling.js b/packages/svelte/src/internal/client/error-handling.js
index 410b1e4a80d6..c462b207cecf 100644
--- a/packages/svelte/src/internal/client/error-handling.js
+++ b/packages/svelte/src/internal/client/error-handling.js
@@ -77,7 +77,7 @@ function should_rethrow_error(effect) {
  * @param {Error} error
  * @param {Effect} effect
  */
-function adjust_error(error, effect) {
+export function adjust_error(error, effect) {
 	if (adjusted_errors.has(error)) return;
 	adjusted_errors.add(error);
 
diff --git a/packages/svelte/src/internal/client/runtime.js b/packages/svelte/src/internal/client/runtime.js
index 7745f975f851..0199f2206923 100644
--- a/packages/svelte/src/internal/client/runtime.js
+++ b/packages/svelte/src/internal/client/runtime.js
@@ -40,7 +40,7 @@ import {
 	set_component_context,
 	set_dev_current_component_function
 } from './context.js';
-import { handle_error, invoke_error_boundary } from './error-handling.js';
+import { adjust_error, handle_error, invoke_error_boundary } from './error-handling.js';
 
 let is_flushing = false;
 
@@ -345,18 +345,17 @@ export function update_reaction(reaction) {
 
 		return result;
 	} catch (error) {
-		// TODO think we can just use active_effect here?
-		var effect = get_effect(reaction);
-
-		if (effect) {
-			if ((effect.f & EFFECT_RAN) !== 0) {
-				invoke_error_boundary(error, effect);
-			} else if ((effect.f & BOUNDARY_EFFECT) !== 0) {
-				// invoke directly
-				effect.fn(error);
-			} else {
-				throw error;
-			}
+		var effect = /** @type {Effect} */ (active_effect);
+
+		if (DEV && error instanceof Error) {
+			adjust_error(error, effect);
+		}
+
+		if ((effect.f & EFFECT_RAN) !== 0) {
+			invoke_error_boundary(error, effect);
+		} else if ((effect.f & BOUNDARY_EFFECT) !== 0) {
+			// invoke directly
+			effect.fn(error);
 		} else {
 			throw error;
 		}

From 4b0ec078560c8f51654ef5b4226da4acda659d44 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Fri, 6 Jun 2025 09:59:53 -0400
Subject: [PATCH 14/29] turns out we need this

---
 .../svelte/src/internal/client/reactivity/effects.js     | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/packages/svelte/src/internal/client/reactivity/effects.js b/packages/svelte/src/internal/client/reactivity/effects.js
index 6c7c21d7dc88..ca1da7f9cd79 100644
--- a/packages/svelte/src/internal/client/reactivity/effects.js
+++ b/packages/svelte/src/internal/client/reactivity/effects.js
@@ -114,8 +114,13 @@ function create_effect(type, fn, sync, push = true) {
 	}
 
 	if (sync) {
-		update_effect(effect);
-		effect.f |= EFFECT_RAN;
+		try {
+			update_effect(effect);
+			effect.f |= EFFECT_RAN;
+		} catch (e) {
+			destroy_effect(effect);
+			throw e;
+		}
 	} else if (fn !== null) {
 		schedule_effect(effect);
 	}

From 9b8439a92d53a7a56cb456d6e56f8f5afb72432f Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Fri, 6 Jun 2025 10:12:52 -0400
Subject: [PATCH 15/29] fix

---
 packages/svelte/src/internal/client/reactivity/effects.js | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/packages/svelte/src/internal/client/reactivity/effects.js b/packages/svelte/src/internal/client/reactivity/effects.js
index ca1da7f9cd79..54994b9bd1cd 100644
--- a/packages/svelte/src/internal/client/reactivity/effects.js
+++ b/packages/svelte/src/internal/client/reactivity/effects.js
@@ -433,7 +433,11 @@ export function destroy_block_effect_children(signal) {
 export function destroy_effect(effect, remove_dom = true) {
 	var removed = false;
 
-	if ((remove_dom || (effect.f & HEAD_EFFECT) !== 0) && effect.nodes_start !== null) {
+	if (
+		(remove_dom || (effect.f & HEAD_EFFECT) !== 0) &&
+		effect.nodes_start !== null &&
+		effect.nodes_end !== null
+	) {
 		remove_effect_dom(effect.nodes_start, /** @type {TemplateNode} */ (effect.nodes_end));
 		removed = true;
 	}

From c4f528a7bff3f9481b8ef4147e1510af1b5f9b0f Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Fri, 6 Jun 2025 11:16:54 -0400
Subject: [PATCH 16/29] all tests passing

---
 .../client/visitors/SvelteBoundary.js         | 81 +++++++++----------
 .../src/internal/client/error-handling.js     |  2 +-
 2 files changed, 41 insertions(+), 42 deletions(-)

diff --git a/packages/svelte/src/compiler/phases/3-transform/client/visitors/SvelteBoundary.js b/packages/svelte/src/compiler/phases/3-transform/client/visitors/SvelteBoundary.js
index ec1c65081496..1480648ce5cc 100644
--- a/packages/svelte/src/compiler/phases/3-transform/client/visitors/SvelteBoundary.js
+++ b/packages/svelte/src/compiler/phases/3-transform/client/visitors/SvelteBoundary.js
@@ -1,4 +1,4 @@
-/** @import { BlockStatement, Statement, Expression } from 'estree' */
+/** @import { BlockStatement, Statement, Expression, FunctionDeclaration, VariableDeclaration, ArrowFunctionExpression } from 'estree' */
 /** @import { AST } from '#compiler' */
 /** @import { ComponentContext } from '../types' */
 import { dev } from '../../../../state.js';
@@ -34,62 +34,61 @@ export function SvelteBoundary(node, context) {
 	const nodes = [];
 
 	/** @type {Statement[]} */
-	const external_statements = [];
+	const const_tags = [];
 
 	/** @type {Statement[]} */
-	const internal_statements = [];
+	const hoisted = [];
 
-	const snippets_visits = [];
+	// const tags need to live inside the boundary, but might also be referenced in hoisted snippets.
+	// to resolve this we cheat: we duplicate const tags inside snippets
+	for (const child of node.fragment.nodes) {
+		if (child.type === 'ConstTag') {
+			context.visit(child, { ...context.state, init: const_tags });
+		}
+	}
 
-	// Capture the `failed` implicit snippet prop
 	for (const child of node.fragment.nodes) {
-		if (child.type === 'SnippetBlock' && child.expression.name === 'failed') {
-			// we need to delay the visit of the snippets in case they access a ConstTag that is declared
-			// after the snippets so that the visitor for the const tag can be updated
-			snippets_visits.push(() => {
-				/** @type {Statement[]} */
-				const init = [];
-				context.visit(child, { ...context.state, init });
-				props.properties.push(b.prop('init', child.expression, child.expression));
-				external_statements.push(...init);
-			});
-		} else if (child.type === 'ConstTag') {
+		if (child.type === 'ConstTag') {
+			continue;
+		}
+
+		if (child.type === 'SnippetBlock') {
 			/** @type {Statement[]} */
-			const init = [];
-			context.visit(child, { ...context.state, init });
-
-			if (dev) {
-				// In dev we must separate the declarations from the code
-				// that eagerly evaluate the expression...
-				for (const statement of init) {
-					if (statement.type === 'VariableDeclaration') {
-						external_statements.push(statement);
-					} else {
-						internal_statements.push(statement);
-					}
-				}
-			} else {
-				external_statements.push(...init);
+			const statements = [];
+
+			context.visit(child, { ...context.state, init: statements });
+
+			const snippet = /** @type {VariableDeclaration} */ (statements[0]);
+
+			const snippet_fn = dev
+				? // @ts-expect-error we know this shape is correct
+					snippet.declarations[0].init.arguments[1]
+				: snippet.declarations[0].init;
+
+			snippet_fn.body.body.unshift(
+				...const_tags.filter((node) => node.type === 'VariableDeclaration')
+			);
+
+			hoisted.push(snippet);
+
+			if (child.expression.name === 'failed') {
+				props.properties.push(b.prop('init', child.expression, child.expression));
 			}
-		} else {
-			nodes.push(child);
+
+			continue;
 		}
-	}
 
-	snippets_visits.forEach((visit) => visit());
+		nodes.push(child);
+	}
 
 	const block = /** @type {BlockStatement} */ (context.visit({ ...node.fragment, nodes }));
 
-	if (dev && internal_statements.length) {
-		block.body.unshift(...internal_statements);
-	}
+	block.body.unshift(...const_tags);
 
 	const boundary = b.stmt(
 		b.call('$.boundary', context.state.node, props, b.arrow([b.id('$$anchor')], block))
 	);
 
 	context.state.template.push_comment();
-	context.state.init.push(
-		external_statements.length > 0 ? b.block([...external_statements, boundary]) : boundary
-	);
+	context.state.init.push(hoisted.length > 0 ? b.block([...hoisted, boundary]) : boundary);
 }
diff --git a/packages/svelte/src/internal/client/error-handling.js b/packages/svelte/src/internal/client/error-handling.js
index c462b207cecf..2e5c31b7a1ab 100644
--- a/packages/svelte/src/internal/client/error-handling.js
+++ b/packages/svelte/src/internal/client/error-handling.js
@@ -81,7 +81,7 @@ export function adjust_error(error, effect) {
 	if (adjusted_errors.has(error)) return;
 	adjusted_errors.add(error);
 
-	const component_stack = [effect.fn?.name ?? '<unknown>'];
+	const component_stack = [effect.fn?.name || '<unknown>'];
 	const indent = is_firefox ? '  ' : '\t';
 
 	var context = effect.ctx;

From 063eab8ce29b2a1757a116c3663efea642edddac Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Fri, 6 Jun 2025 11:18:43 -0400
Subject: [PATCH 17/29] unused

---
 .../internal/client/dom/blocks/boundary.js    |  5 +----
 .../src/internal/client/error-handling.js     | 19 +------------------
 2 files changed, 2 insertions(+), 22 deletions(-)

diff --git a/packages/svelte/src/internal/client/dom/blocks/boundary.js b/packages/svelte/src/internal/client/dom/blocks/boundary.js
index 2387b22f5198..20839a778368 100644
--- a/packages/svelte/src/internal/client/dom/blocks/boundary.js
+++ b/packages/svelte/src/internal/client/dom/blocks/boundary.js
@@ -2,7 +2,7 @@
 
 import { BOUNDARY_EFFECT, EFFECT_TRANSPARENT } from '#client/constants';
 import { component_context, set_component_context } from '../../context.js';
-import { invoke_error_boundary, reset_is_throwing_error } from '../../error-handling.js';
+import { invoke_error_boundary } from '../../error-handling.js';
 import { block, branch, destroy_effect, pause_effect } from '../../reactivity/effects.js';
 import {
 	active_effect,
@@ -80,7 +80,6 @@ export function boundary(node, props, boundary_fn) {
 				with_boundary(boundary, () => {
 					is_creating_fallback = false;
 					boundary_effect = branch(() => boundary_fn(anchor));
-					reset_is_throwing_error();
 				});
 			};
 
@@ -119,7 +118,6 @@ export function boundary(node, props, boundary_fn) {
 							invoke_error_boundary(error, /** @type {Effect} */ (boundary.parent));
 						}
 
-						reset_is_throwing_error();
 						is_creating_fallback = false;
 					});
 				});
@@ -131,7 +129,6 @@ export function boundary(node, props, boundary_fn) {
 		}
 
 		boundary_effect = branch(() => boundary_fn(anchor));
-		reset_is_throwing_error();
 	}, EFFECT_TRANSPARENT | BOUNDARY_EFFECT);
 
 	if (hydrating) {
diff --git a/packages/svelte/src/internal/client/error-handling.js b/packages/svelte/src/internal/client/error-handling.js
index 2e5c31b7a1ab..c27ba1a3607f 100644
--- a/packages/svelte/src/internal/client/error-handling.js
+++ b/packages/svelte/src/internal/client/error-handling.js
@@ -2,19 +2,13 @@
 import { DEV } from 'esm-env';
 import { FILENAME } from '../../constants.js';
 import { is_firefox } from './dom/operations.js';
-import { BOUNDARY_EFFECT, DESTROYED } from './constants.js';
+import { BOUNDARY_EFFECT } from './constants.js';
 import { define_property } from '../shared/utils.js';
 
 // Used for DEV time error handling
 /** @param {WeakSet<Error>} value */
 const adjusted_errors = new WeakSet();
 
-let is_throwing_error = false;
-
-export function reset_is_throwing_error() {
-	is_throwing_error = false;
-}
-
 /** @type {null | unknown} */
 let current_error = null;
 
@@ -58,20 +52,9 @@ export function invoke_error_boundary(error, effect) {
 		current = current.parent;
 	}
 
-	is_throwing_error = false;
 	throw error;
 }
 
-/**
- * @param {Effect} effect
- */
-function should_rethrow_error(effect) {
-	return (
-		(effect.f & DESTROYED) === 0 &&
-		(effect.parent === null || (effect.parent.f & BOUNDARY_EFFECT) === 0)
-	);
-}
-
 /**
  * Add useful information to the error message/stack
  * @param {Error} error

From 47372dfb16848ef1932ae5efd607caf744ee4658 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Fri, 6 Jun 2025 11:19:51 -0400
Subject: [PATCH 18/29] unused

---
 packages/svelte/src/internal/client/error-handling.js | 8 --------
 1 file changed, 8 deletions(-)

diff --git a/packages/svelte/src/internal/client/error-handling.js b/packages/svelte/src/internal/client/error-handling.js
index c27ba1a3607f..9613cfa798a0 100644
--- a/packages/svelte/src/internal/client/error-handling.js
+++ b/packages/svelte/src/internal/client/error-handling.js
@@ -9,19 +9,11 @@ import { define_property } from '../shared/utils.js';
 /** @param {WeakSet<Error>} value */
 const adjusted_errors = new WeakSet();
 
-/** @type {null | unknown} */
-let current_error = null;
-
 /**
  * @param {unknown} error
  * @param {Effect} effect
  */
 export function handle_error(error, effect) {
-	if (error === current_error) {
-		// TODO is this necessary?
-		return;
-	}
-
 	if (DEV && error instanceof Error) {
 		adjust_error(error, effect);
 	}

From 786b50a48d42269499d9a373ab619671ff49218c Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Fri, 6 Jun 2025 11:24:54 -0400
Subject: [PATCH 19/29] tidy up

---
 .../src/internal/client/error-handling.js     | 19 +++++++++----
 .../svelte/src/internal/client/runtime.js     | 27 +++++--------------
 2 files changed, 20 insertions(+), 26 deletions(-)

diff --git a/packages/svelte/src/internal/client/error-handling.js b/packages/svelte/src/internal/client/error-handling.js
index 9613cfa798a0..66e93bea102d 100644
--- a/packages/svelte/src/internal/client/error-handling.js
+++ b/packages/svelte/src/internal/client/error-handling.js
@@ -2,8 +2,9 @@
 import { DEV } from 'esm-env';
 import { FILENAME } from '../../constants.js';
 import { is_firefox } from './dom/operations.js';
-import { BOUNDARY_EFFECT } from './constants.js';
+import { BOUNDARY_EFFECT, EFFECT_RAN } from './constants.js';
 import { define_property } from '../shared/utils.js';
+import { active_effect } from './runtime.js';
 
 // Used for DEV time error handling
 /** @param {WeakSet<Error>} value */
@@ -11,14 +12,22 @@ const adjusted_errors = new WeakSet();
 
 /**
  * @param {unknown} error
- * @param {Effect} effect
  */
-export function handle_error(error, effect) {
+export function handle_error(error) {
+	var effect = /** @type {Effect} */ (active_effect);
+
 	if (DEV && error instanceof Error) {
 		adjust_error(error, effect);
 	}
 
-	invoke_error_boundary(error, effect);
+	if ((effect.f & EFFECT_RAN) !== 0) {
+		invoke_error_boundary(error, effect);
+	} else if ((effect.f & BOUNDARY_EFFECT) !== 0) {
+		// invoke directly
+		effect.fn(error);
+	} else {
+		throw error;
+	}
 }
 
 /**
@@ -52,7 +61,7 @@ export function invoke_error_boundary(error, effect) {
  * @param {Error} error
  * @param {Effect} effect
  */
-export function adjust_error(error, effect) {
+function adjust_error(error, effect) {
 	if (adjusted_errors.has(error)) return;
 	adjusted_errors.add(error);
 
diff --git a/packages/svelte/src/internal/client/runtime.js b/packages/svelte/src/internal/client/runtime.js
index 0199f2206923..a60a25ad06e5 100644
--- a/packages/svelte/src/internal/client/runtime.js
+++ b/packages/svelte/src/internal/client/runtime.js
@@ -1,4 +1,4 @@
-/** @import { ComponentContext, Derived, Effect, Reaction, Signal, Source, Value } from '#client' */
+/** @import { Derived, Effect, Reaction, Signal, Source, Value } from '#client' */
 import { DEV } from 'esm-env';
 import { define_property, get_descriptors, get_prototype_of, index_of } from '../shared/utils.js';
 import {
@@ -22,9 +22,7 @@ import {
 	ROOT_EFFECT,
 	LEGACY_DERIVED_PROP,
 	DISCONNECTED,
-	BOUNDARY_EFFECT,
-	EFFECT_IS_UPDATING,
-	EFFECT_RAN
+	EFFECT_IS_UPDATING
 } from './constants.js';
 import { flush_tasks } from './dom/task.js';
 import { internal_set, old_values } from './reactivity/sources.js';
@@ -40,7 +38,7 @@ import {
 	set_component_context,
 	set_dev_current_component_function
 } from './context.js';
-import { adjust_error, handle_error, invoke_error_boundary } from './error-handling.js';
+import { handle_error, invoke_error_boundary } from './error-handling.js';
 
 let is_flushing = false;
 
@@ -345,20 +343,7 @@ export function update_reaction(reaction) {
 
 		return result;
 	} catch (error) {
-		var effect = /** @type {Effect} */ (active_effect);
-
-		if (DEV && error instanceof Error) {
-			adjust_error(error, effect);
-		}
-
-		if ((effect.f & EFFECT_RAN) !== 0) {
-			invoke_error_boundary(error, effect);
-		} else if ((effect.f & BOUNDARY_EFFECT) !== 0) {
-			// invoke directly
-			effect.fn(error);
-		} else {
-			throw error;
-		}
+		handle_error(error);
 	} finally {
 		new_deps = previous_deps;
 		skipped_deps = previous_skipped_deps;
@@ -532,14 +517,14 @@ function infinite_loop_guard() {
 		if (last_scheduled_effect !== null) {
 			if (DEV) {
 				try {
-					handle_error(error, last_scheduled_effect);
+					invoke_error_boundary(error, last_scheduled_effect);
 				} catch (e) {
 					// Only log the effect stack if the error is re-thrown
 					log_effect_stack();
 					throw e;
 				}
 			} else {
-				handle_error(error, last_scheduled_effect);
+				invoke_error_boundary(error, last_scheduled_effect);
 			}
 		} else {
 			if (DEV) {

From 0e091157a9a7b5298972a4bd9849948a74b42139 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Fri, 6 Jun 2025 11:32:00 -0400
Subject: [PATCH 20/29] unused

---
 packages/svelte/src/internal/client/error-handling.js | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/packages/svelte/src/internal/client/error-handling.js b/packages/svelte/src/internal/client/error-handling.js
index 66e93bea102d..9f0838e8cb5e 100644
--- a/packages/svelte/src/internal/client/error-handling.js
+++ b/packages/svelte/src/internal/client/error-handling.js
@@ -44,10 +44,7 @@ export function invoke_error_boundary(error, effect) {
 				// @ts-expect-error
 				current.fn(error);
 				return;
-			} catch {
-				// Remove boundary flag from effect (TODO is this still useful?)
-				current.f ^= BOUNDARY_EFFECT;
-			}
+			} catch {}
 		}
 
 		current = current.parent;

From 0bbceee45f6057d65ae1875ece8ec9dcb1d8ef06 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Fri, 6 Jun 2025 11:43:33 -0400
Subject: [PATCH 21/29] unused

---
 packages/svelte/src/internal/client/error-handling.js | 5 -----
 1 file changed, 5 deletions(-)

diff --git a/packages/svelte/src/internal/client/error-handling.js b/packages/svelte/src/internal/client/error-handling.js
index 9f0838e8cb5e..367606d7582d 100644
--- a/packages/svelte/src/internal/client/error-handling.js
+++ b/packages/svelte/src/internal/client/error-handling.js
@@ -76,11 +76,6 @@ function adjust_error(error, effect) {
 		value: error.message + `\n${component_stack.map((name) => `\n${indent}in ${name}`).join('')}\n`
 	});
 
-	// TODO what is this for? can we get rid of it?
-	define_property(error, 'component_stack', {
-		value: component_stack
-	});
-
 	// Filter out internal files from callstack
 	if (error.stack) {
 		define_property(error, 'stack', {

From e243091d461acc0a7c08b05165a73faff8effb8f Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Fri, 6 Jun 2025 11:47:29 -0400
Subject: [PATCH 22/29] tweak

---
 packages/svelte/src/internal/client/error-handling.js | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/packages/svelte/src/internal/client/error-handling.js b/packages/svelte/src/internal/client/error-handling.js
index 367606d7582d..a13c205166ac 100644
--- a/packages/svelte/src/internal/client/error-handling.js
+++ b/packages/svelte/src/internal/client/error-handling.js
@@ -62,22 +62,21 @@ function adjust_error(error, effect) {
 	if (adjusted_errors.has(error)) return;
 	adjusted_errors.add(error);
 
-	const component_stack = [effect.fn?.name || '<unknown>'];
-	const indent = is_firefox ? '  ' : '\t';
-
+	var indent = is_firefox ? '  ' : '\t';
+	var component_stack = `\n${indent}in ${effect.fn?.name || '<unknown>'}`;
 	var context = effect.ctx;
 
 	while (context !== null) {
-		component_stack.push(context.function?.[FILENAME].split('/').pop());
+		component_stack += `\n${indent}in ${context.function?.[FILENAME].split('/').pop()}`;
 		context = context.p;
 	}
 
 	define_property(error, 'message', {
-		value: error.message + `\n${component_stack.map((name) => `\n${indent}in ${name}`).join('')}\n`
+		value: error.message + `\n${component_stack}\n`
 	});
 
-	// Filter out internal files from callstack
 	if (error.stack) {
+		// Filter out internal modules
 		define_property(error, 'stack', {
 			value: error.stack
 				.split('\n')

From 91458a012d1334407eb9c75a6b0a86c9db202fff Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Fri, 6 Jun 2025 12:17:23 -0400
Subject: [PATCH 23/29] WIP

---
 .../svelte/src/internal/client/error-handling.js  | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/packages/svelte/src/internal/client/error-handling.js b/packages/svelte/src/internal/client/error-handling.js
index a13c205166ac..be99c5efda4c 100644
--- a/packages/svelte/src/internal/client/error-handling.js
+++ b/packages/svelte/src/internal/client/error-handling.js
@@ -20,13 +20,18 @@ export function handle_error(error) {
 		adjust_error(error, effect);
 	}
 
-	if ((effect.f & EFFECT_RAN) !== 0) {
-		invoke_error_boundary(error, effect);
-	} else if ((effect.f & BOUNDARY_EFFECT) !== 0) {
-		// invoke directly
+	if ((effect.f & EFFECT_RAN) === 0) {
+		// if the error occurred while creating this subtree, we let it
+		// bubble up until it hits a boundary that can handle it
+		if ((effect.f & BOUNDARY_EFFECT) === 0) {
+			throw error;
+		}
+
+		// @ts-expect-error
 		effect.fn(error);
 	} else {
-		throw error;
+		// otherwise we bubble up the effect tree ourselves
+		invoke_error_boundary(error, effect);
 	}
 }
 

From 0a433d92c6e95f267c8b3bb5be2e8a47b9ac1618 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Fri, 6 Jun 2025 12:20:33 -0400
Subject: [PATCH 24/29] tweak

---
 .../svelte/src/internal/client/error-handling.js    | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/packages/svelte/src/internal/client/error-handling.js b/packages/svelte/src/internal/client/error-handling.js
index be99c5efda4c..8baa1eced55c 100644
--- a/packages/svelte/src/internal/client/error-handling.js
+++ b/packages/svelte/src/internal/client/error-handling.js
@@ -37,22 +37,19 @@ export function handle_error(error) {
 
 /**
  * @param {unknown} error
- * @param {Effect} effect
+ * @param {Effect | null} effect
  */
 export function invoke_error_boundary(error, effect) {
-	/** @type {Effect | null} */
-	var current = effect;
-
-	while (current !== null) {
-		if ((current.f & BOUNDARY_EFFECT) !== 0) {
+	while (effect !== null) {
+		if ((effect.f & BOUNDARY_EFFECT) !== 0) {
 			try {
 				// @ts-expect-error
-				current.fn(error);
+				effect.fn(error);
 				return;
 			} catch {}
 		}
 
-		current = current.parent;
+		effect = effect.parent;
 	}
 
 	throw error;

From a45aab670e0fd61920e82628d7ca2971a68e9546 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Fri, 6 Jun 2025 12:23:07 -0400
Subject: [PATCH 25/29] asked and answered

---
 packages/svelte/src/internal/client/dom/blocks/boundary.js | 1 -
 1 file changed, 1 deletion(-)

diff --git a/packages/svelte/src/internal/client/dom/blocks/boundary.js b/packages/svelte/src/internal/client/dom/blocks/boundary.js
index 20839a778368..d7a53da1d131 100644
--- a/packages/svelte/src/internal/client/dom/blocks/boundary.js
+++ b/packages/svelte/src/internal/client/dom/blocks/boundary.js
@@ -74,7 +74,6 @@ export function boundary(node, props, boundary_fn) {
 			}
 
 			var reset = () => {
-				// TODO does this make sense?
 				pause_effect(boundary_effect);
 
 				with_boundary(boundary, () => {

From 9f0c1f7950dec891d213f199506715df46908cab Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Fri, 6 Jun 2025 12:25:26 -0400
Subject: [PATCH 26/29] tweak

---
 packages/svelte/src/internal/client/error-handling.js | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/packages/svelte/src/internal/client/error-handling.js b/packages/svelte/src/internal/client/error-handling.js
index 8baa1eced55c..aeec1d8b473d 100644
--- a/packages/svelte/src/internal/client/error-handling.js
+++ b/packages/svelte/src/internal/client/error-handling.js
@@ -6,10 +6,6 @@ import { BOUNDARY_EFFECT, EFFECT_RAN } from './constants.js';
 import { define_property } from '../shared/utils.js';
 import { active_effect } from './runtime.js';
 
-// Used for DEV time error handling
-/** @param {WeakSet<Error>} value */
-const adjusted_errors = new WeakSet();
-
 /**
  * @param {unknown} error
  */
@@ -55,8 +51,11 @@ export function invoke_error_boundary(error, effect) {
 	throw error;
 }
 
+/** @type {WeakSet<Error>} */
+const adjusted_errors = new WeakSet();
+
 /**
- * Add useful information to the error message/stack
+ * Add useful information to the error message/stack in development
  * @param {Error} error
  * @param {Effect} effect
  */

From 610c252964769c2cebeeaa98d4bc0bbba18db202 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Fri, 6 Jun 2025 12:26:18 -0400
Subject: [PATCH 27/29] unused

---
 packages/svelte/src/internal/client/runtime.js | 12 ------------
 1 file changed, 12 deletions(-)

diff --git a/packages/svelte/src/internal/client/runtime.js b/packages/svelte/src/internal/client/runtime.js
index a60a25ad06e5..ceb145779884 100644
--- a/packages/svelte/src/internal/client/runtime.js
+++ b/packages/svelte/src/internal/client/runtime.js
@@ -358,18 +358,6 @@ export function update_reaction(reaction) {
 	}
 }
 
-/** @param {Reaction} reaction */
-function get_effect(reaction) {
-	/** @type {Reaction | null;} */
-	var r = reaction;
-
-	while (r !== null && (r.f & DERIVED) !== 0) {
-		r = /** @type {Derived} */ (r).parent;
-	}
-
-	return /** @type {Effect | null} */ (r);
-}
-
 /**
  * @template V
  * @param {Reaction} signal

From eedaa258b6400ad2247cc1faf41de180c4f13df2 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Fri, 6 Jun 2025 12:28:06 -0400
Subject: [PATCH 28/29] changeset

---
 .changeset/early-tips-prove.md | 5 +++++
 1 file changed, 5 insertions(+)
 create mode 100644 .changeset/early-tips-prove.md

diff --git a/.changeset/early-tips-prove.md b/.changeset/early-tips-prove.md
new file mode 100644
index 000000000000..2df03126d890
--- /dev/null
+++ b/.changeset/early-tips-prove.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: invoke parent boundary of deriveds that throw

From da2c8a9611657590e38d5ca6d6dc63067da55ba3 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Fri, 6 Jun 2025 12:52:44 -0400
Subject: [PATCH 29/29] lint

---
 packages/svelte/src/internal/client/runtime.js | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/packages/svelte/src/internal/client/runtime.js b/packages/svelte/src/internal/client/runtime.js
index ceb145779884..5920a05fc50d 100644
--- a/packages/svelte/src/internal/client/runtime.js
+++ b/packages/svelte/src/internal/client/runtime.js
@@ -248,11 +248,7 @@ function schedule_possible_effect_self_invalidation(signal, effect, root = true)
 	}
 }
 
-/**
- * @template V
- * @param {Reaction} reaction
- * @returns {V}
- */
+/** @param {Reaction} reaction */
 export function update_reaction(reaction) {
 	var previous_deps = new_deps;
 	var previous_skipped_deps = skipped_deps;