fix: ensure infinite effect loops are cleared after flushing (#17601)

* failing effect-loop-infinite test

* fix

.changeset/chatty-mammals-find.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: ensure infinite effect loops are cleared after flushing

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

@@ -647,8 +647,9 @@ function flush_effects() {
 			}
 		}
 	} finally {
-		is_flushing = false;
+		queued_root_effects = [];
 
+		is_flushing = false;
 		last_scheduled_effect = null;
 
 		if (DEV) {

packages/svelte/tests/runtime-legacy/shared.ts

@@ -521,6 +521,8 @@ async function run_test_variant(
 						errors,
 						hydrate: hydrate_fn
 					});
+
+					flushSync();
 				}
 
 				if (config.runtime_error && !unhandled_rejection) {

packages/svelte/tests/runtime-runes/samples/effect-loop-infinite/_config.js

@@ -11,11 +11,12 @@ export default test({
 	test({ assert, errors }) {
 		const [button] = document.querySelectorAll('button');
 
-		try {
+		assert.throws(() => {
 			flushSync(() => button.click());
-		} catch (e) {
-			assert.equal(errors.length, 1); // for whatever reason we can't get the name which should be 'updated at'
-			assert.ok(/** @type {Error} */ (e).message.startsWith('effect_update_depth_exceeded'));
-		}
+		}, /effect_update_depth_exceeded/);
+
+		assert.equal(errors.length, 1);
+
+		assert.doesNotThrow(flushSync);
 	}
 });