From da2f83343bf5e2fb183881b74ef06fac24f0e249 Mon Sep 17 00:00:00 2001
From: Simon H <5968653+dummdidumm@users.noreply.github.com>
Date: Thu, 24 Sep 2026 22:47:52 +0200
Subject: [PATCH 1/2] fix: read batch-local array on each-block commit (#18879)

Another extraction from #18861 which I'm pretty sure you can also
construct a buggy reproduction for today, but with #18861 it's strictly
necessary so we don't need to come up with one now
---
 .changeset/short-radios-sneeze.md                      |  5 +++++
 packages/svelte/src/internal/client/dom/blocks/each.js | 10 ++++++----
 2 files changed, 11 insertions(+), 4 deletions(-)
 create mode 100644 .changeset/short-radios-sneeze.md

diff --git a/.changeset/short-radios-sneeze.md b/.changeset/short-radios-sneeze.md
new file mode 100644
index 0000000000..847c3eef17
--- /dev/null
+++ b/.changeset/short-radios-sneeze.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: read batch-local array on each-block commit
diff --git a/packages/svelte/src/internal/client/dom/blocks/each.js b/packages/svelte/src/internal/client/dom/blocks/each.js
index ea828f893b..58d59a6825 100644
--- a/packages/svelte/src/internal/client/dom/blocks/each.js
+++ b/packages/svelte/src/internal/client/dom/blocks/each.js
@@ -216,9 +216,6 @@ export function each(node, flags, get_collection, get_key, render_fn, fallback_f
 		tag(each_array, '{#each ...}');
 	}
 
-	/** @type {V[]} */
-	var array;
-
 	/** @type {Map<Batch, Set<any>>} */
 	var pending = new Map();
 
@@ -234,6 +231,11 @@ export function each(node, flags, get_collection, get_key, render_fn, fallback_f
 
 		state.pending.delete(batch);
 
+		// The effect doesn't necessarily re-run in a batch right before that batch commits
+		// (its view of the collection may not have changed), so we read the collection
+		// as the committing batch sees it rather than using the most recent block run's result
+		var array = get(each_array);
+
 		state.fallback = fallback;
 		reconcile(state, array, anchor, flags, get_key);
 
@@ -264,7 +266,7 @@ export function each(node, flags, get_collection, get_key, render_fn, fallback_f
 	}
 
 	var effect = block(() => {
-		array = /** @type {V[]} */ (get(each_array));
+		var array = /** @type {V[]} */ (get(each_array));
 		var length = array.length;
 
 		/** `true` if there was a hydration mismatch. Needs to be a `let` or else it isn't treeshaken out */

From 98e547535d9286cfd4163fe3a6d85c7053db6c6e Mon Sep 17 00:00:00 2001
From: Simon H <5968653+dummdidumm@users.noreply.github.com>
Date: Thu, 24 Sep 2026 22:49:15 +0200
Subject: [PATCH 2/2] fix: flush anything pending before invoking flushSync
 callback function (#18878)

no new test here but it's necessary for #18861 to work, and we might as
well extract it
---
 .changeset/major-papayas-run.md                      |  5 +++++
 .../svelte/src/internal/client/reactivity/batch.js   | 12 ++++++++----
 2 files changed, 13 insertions(+), 4 deletions(-)
 create mode 100644 .changeset/major-papayas-run.md

diff --git a/.changeset/major-papayas-run.md b/.changeset/major-papayas-run.md
new file mode 100644
index 0000000000..59909fb448
--- /dev/null
+++ b/.changeset/major-papayas-run.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: flush anything pending before invoking flushSync callback function
diff --git a/packages/svelte/src/internal/client/reactivity/batch.js b/packages/svelte/src/internal/client/reactivity/batch.js
index f620c2b4c8..05f7586072 100644
--- a/packages/svelte/src/internal/client/reactivity/batch.js
+++ b/packages/svelte/src/internal/client/reactivity/batch.js
@@ -1032,15 +1032,15 @@ export class Batch {
  */
 export function flushSync(fn) {
 	var was_flushing_sync = is_flushing_sync;
+	var prev_previous_batch = previous_batch;
+	previous_batch = null;
 	is_flushing_sync = true;
 
 	try {
 		var result;
 
 		if (fn) {
-			if (current_batch !== null && !current_batch.is_fork) {
-				current_batch.flush();
-			}
+			flushSync(); // flush anything pending through the while loop below
 
 			result = fn();
 		}
@@ -1056,6 +1056,7 @@ export function flushSync(fn) {
 		}
 	} finally {
 		is_flushing_sync = was_flushing_sync;
+		previous_batch = prev_previous_batch;
 	}
 }
 
@@ -1406,6 +1407,8 @@ export function fork(fn) {
 		e.fork_timing();
 	}
 
+	flushSync();
+
 	var batch = Batch.ensure();
 	batch.is_fork = true;
 	batch_values = new Map();
@@ -1413,7 +1416,8 @@ export function fork(fn) {
 	var committed = false;
 	var settled = batch.settled();
 
-	flushSync(fn);
+	fn();
+	flushSync();
 
 	return {
 		commit: async () => {