From e6206ce4824db907f30787a7fcf0d361c42e62a4 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Thu, 2 Apr 2026 16:39:07 -0400
Subject: [PATCH] bail out of mark_reactions if wv > cv

---
 .../src/internal/client/reactivity/batch.js   |  4 ++--
 .../src/internal/client/reactivity/sources.js | 22 +++++++++++--------
 2 files changed, 15 insertions(+), 11 deletions(-)

diff --git a/packages/svelte/src/internal/client/reactivity/batch.js b/packages/svelte/src/internal/client/reactivity/batch.js
index f895b01faf..9219f23b45 100644
--- a/packages/svelte/src/internal/client/reactivity/batch.js
+++ b/packages/svelte/src/internal/client/reactivity/batch.js
@@ -274,8 +274,8 @@ export class Batch {
 			infinite_loop_guard();
 		}
 
-		for (const source of this.current.keys()) {
-			mark_reactions(source, null);
+		for (const [source, wv] of this.wvs) {
+			mark_reactions(source, wv, null);
 		}
 
 		// we only reschedule previously-deferred effects if we expect
diff --git a/packages/svelte/src/internal/client/reactivity/sources.js b/packages/svelte/src/internal/client/reactivity/sources.js
index 1a7cbca886..ae837b9bd7 100644
--- a/packages/svelte/src/internal/client/reactivity/sources.js
+++ b/packages/svelte/src/internal/client/reactivity/sources.js
@@ -40,7 +40,8 @@ import {
 	eager_block_effects,
 	schedule_effect,
 	legacy_updates,
-	set_cv
+	set_cv,
+	get_cv
 } from './batch.js';
 import { proxy } from '../proxy.js';
 import { execute_derived } from './deriveds.js';
@@ -231,7 +232,7 @@ export function internal_set(source, value, updated_during_traversal = null) {
 
 		// For debugging, in case you want to know which reactions are being scheduled:
 		// log_reactions(source);
-		mark_reactions(source, updated_during_traversal);
+		mark_reactions(source, write_version, updated_during_traversal);
 
 		// It's possible that the current reaction might not have up-to-date dependencies
 		// whilst it's actively running. So in the case of ensuring it registers the reaction
@@ -310,10 +311,11 @@ export function increment(source) {
 
 /**
  * @param {Value} signal
+ * @param {number} wv
  * @param {Effect[] | null} updated_during_traversal
  * @returns {void}
  */
-export function mark_reactions(signal, updated_during_traversal) {
+export function mark_reactions(signal, wv, updated_during_traversal) {
 	var reactions = signal.reactions;
 	if (reactions === null) return;
 
@@ -338,13 +340,15 @@ export function mark_reactions(signal, updated_during_traversal) {
 
 			batch_values?.delete(derived);
 
-			if ((flags & WAS_MARKED) === 0) {
-				// Only connected deriveds can be reliably unmarked right away
-				if (flags & CONNECTED) {
-					reaction.f |= WAS_MARKED;
-				}
+			if (wv > get_cv(derived)) {
+				if ((flags & WAS_MARKED) === 0) {
+					// Only connected deriveds can be reliably unmarked right away
+					if (flags & CONNECTED) {
+						reaction.f |= WAS_MARKED;
+					}
 
-				mark_reactions(derived, updated_during_traversal);
+					mark_reactions(derived, wv, updated_during_traversal);
+				}
 			}
 		} else {
 			var effect = /** @type {Effect} */ (reaction);