From 652103bb9fcf0036fcb5bb72aa0f5cc06be5969a Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Tue, 13 Oct 2026 12:07:20 -0400
Subject: [PATCH] restore is_eager early return in #find_earlier_batch

An eager batch sees other batches' previous values, so its async results must not resolve an
earlier batch's work. It can still get a dependency via the in-flight check in async_derived.
---
 .../src/internal/client/reactivity/batch.js   |  2 +
 .../async-eager-batch-no-merge/_config.js     | 44 +++++++++++++++++++
 .../async-eager-batch-no-merge/main.svelte    | 20 +++++++++
 3 files changed, 66 insertions(+)
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-eager-batch-no-merge/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/async-eager-batch-no-merge/main.svelte

diff --git a/packages/svelte/src/internal/client/reactivity/batch.js b/packages/svelte/src/internal/client/reactivity/batch.js
index dd230d3787..f4c70c822f 100644
--- a/packages/svelte/src/internal/client/reactivity/batch.js
+++ b/packages/svelte/src/internal/client/reactivity/batch.js
@@ -609,6 +609,8 @@ export class Batch {
 	}
 
 	#find_earlier_batch() {
+		if (this.is_eager) return null;
+
 		for (var batch = this.prev; batch !== null; batch = batch.prev) {
 			if (!batch.is_fork && this.dependent.has(batch)) {
 				return batch;
diff --git a/packages/svelte/tests/runtime-runes/samples/async-eager-batch-no-merge/_config.js b/packages/svelte/tests/runtime-runes/samples/async-eager-batch-no-merge/_config.js
new file mode 100644
index 0000000000..f90497846c
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-eager-batch-no-merge/_config.js
@@ -0,0 +1,44 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+const buttons =
+	'<button>page</button><button>filter</button><button>shift</button><button>pop</button>';
+
+// The eager batch that re-runs `load` for the new `$state.eager(filter)` value computes it
+// with the old `page`, because eager batches don't see other batches' changes. Therefore it
+// must not be merged into the (pending) `page` batch — else its result would resolve that
+// batch's `load(2, ...)` and be shown next to `page: 2`
+export default test({
+	async test({ assert, target }) {
+		await tick();
+		const [page, filter, shift, pop] = target.querySelectorAll('button');
+
+		// B1: page = 2 -> load(2, 'a') pending
+		page.click();
+		await tick();
+		assert.htmlEqual(target.innerHTML, `${buttons}<p>page: 1</p><p>result: 1/a</p>`);
+
+		// filter = 'b' -> eager batch re-runs load(1, 'b'), pending
+		filter.click();
+		await tick();
+		assert.htmlEqual(target.innerHTML, `${buttons}<p>page: 1</p><p>result: 1/a</p>`);
+
+		// resolve load(1, 'b') -> the eager batch commits on its own
+		pop.click();
+		await tick();
+		assert.htmlEqual(target.innerHTML, `${buttons}<p>page: 1</p><p>result: 1/b</p>`);
+
+		// resolve load(2, 'a') -> B1 commits (showing B1's own result is fine, as is
+		// waiting for load(2, 'b'), as long as the result matches the page)
+		shift.click();
+		await tick();
+		const [p1, p2] = target.querySelectorAll('p');
+		assert.equal(p1.textContent, 'page: 2');
+		assert.match(p2.textContent ?? '', /^result: 2\//);
+
+		// load(2, 'b') resolves
+		shift.click();
+		await tick();
+		assert.htmlEqual(target.innerHTML, `${buttons}<p>page: 2</p><p>result: 2/b</p>`);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-eager-batch-no-merge/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-eager-batch-no-merge/main.svelte
new file mode 100644
index 0000000000..008fabe2e5
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-eager-batch-no-merge/main.svelte
@@ -0,0 +1,20 @@
+<script>
+	let page = $state(1);
+	let filter = $state('a');
+
+	const deferred = [];
+
+	function load(page, filter) {
+		const value = `${page}/${filter}`;
+		if (value === '1/a') return value;
+		return new Promise((resolve) => deferred.push(() => resolve(value)));
+	}
+</script>
+
+<button onclick={() => page++}>page</button>
+<button onclick={() => (filter = 'b')}>filter</button>
+<button onclick={() => deferred.shift()?.()}>shift</button>
+<button onclick={() => deferred.pop()?.()}>pop</button>
+
+<p>page: {page}</p>
+<p>result: {await load(page, $state.eager(filter))}</p>