fix: mark reactions of MAYBE_DIRTY reactions too

.changeset/sour-jars-sniff.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: mark reactions of `MAYBE_DIRTY` reactions too

packages/svelte/src/internal/client/reactivity/sources.js

@@ -329,7 +329,7 @@ function mark_reactions(signal, status) {
 		set_signal_status(reaction, status);
 
 		// If the signal a) was previously clean or b) is an unowned derived, then mark it
-		if ((flags & (CLEAN | UNOWNED)) !== 0) {
+		if ((flags & (CLEAN | UNOWNED | MAYBE_DIRTY)) !== 0) {
 			if ((flags & DERIVED) !== 0) {
 				mark_reactions(/** @type {Derived} */ (reaction), MAYBE_DIRTY);
 			} else {

packages/svelte/tests/runtime-runes/samples/derived-dirty-after-read/A.svelte

@@ -0,0 +1,10 @@
+<script>
+	let {config, value = $bindable()} = $props();
+
+	$effect.pre(() => {
+		config;
+		value = {}
+	});
+</script>
+
+a

packages/svelte/tests/runtime-runes/samples/derived-dirty-after-read/B.svelte

@@ -0,0 +1,10 @@
+<script>
+	let {config, value = $bindable()} = $props();
+
+	$effect.pre(() => {
+		config;
+		value = {}
+	});
+</script>
+
+b

packages/svelte/tests/runtime-runes/samples/derived-dirty-after-read/_config.js

@@ -0,0 +1,14 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	html: '<button></button> a',
+	async test({ assert, target }) {
+		const btn = target.querySelector('button');
+		flushSync(() => {
+			btn?.click();
+		});
+
+		assert.htmlEqual(target.innerHTML, `<button></button> b`);
+	}
+});

packages/svelte/tests/runtime-runes/samples/derived-dirty-after-read/main.svelte

@@ -0,0 +1,22 @@
+<script>
+	import A from "./A.svelte";
+	import B from "./B.svelte";
+
+	let schema = $state("any");
+	let value = $state({});
+
+	let config = $derived.by(() => {
+		value;
+		return schema;
+	});
+
+	let Thing = $derived.by(() => {
+		return config === "any" ? A : B;
+	});
+</script>
+
+<button onclick={()=>{
+	schema = "one";
+}}></button>
+
+<Thing {config} bind:value/>