diff --git a/.changeset/clean-melons-attack.md b/.changeset/clean-melons-attack.md
deleted file mode 100644
index 8b5a9f2066..0000000000
--- a/.changeset/clean-melons-attack.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: include wrapping parentheses in `{@const}` declarator `end` position
diff --git a/.changeset/quick-meals-shout.md b/.changeset/quick-meals-shout.md
deleted file mode 100644
index 21871edd67..0000000000
--- a/.changeset/quick-meals-shout.md
+++ /dev/null
@@ -1,5 +0,0 @@
----
-'svelte': patch
----
-
-fix: don't notify `searchParams` subscribers when the URL changes without affecting the search string
diff --git a/packages/svelte/CHANGELOG.md b/packages/svelte/CHANGELOG.md
index 02dd84ddff..80b61facb0 100644
--- a/packages/svelte/CHANGELOG.md
+++ b/packages/svelte/CHANGELOG.md
@@ -1,5 +1,17 @@
 # svelte
 
+## 5.56.4
+
+### Patch Changes
+
+- fix: include wrapping parentheses in `{@const}` declarator `end` position ([#18436](https://github.com/sveltejs/svelte/pull/18436))
+
+- fix: always unset reactivity context after restoring it ([#18453](https://github.com/sveltejs/svelte/pull/18453))
+
+- fix: don't notify `searchParams` subscribers when the URL changes without affecting the search string ([#18425](https://github.com/sveltejs/svelte/pull/18425))
+
+- fix: strip `?` from optional parameters in `<script lang="ts">` so generated JavaScript is valid ([#18448](https://github.com/sveltejs/svelte/pull/18448))
+
 ## 5.56.3
 
 ### Patch Changes
diff --git a/packages/svelte/package.json b/packages/svelte/package.json
index ccfa87cc2e..c875fe1b16 100644
--- a/packages/svelte/package.json
+++ b/packages/svelte/package.json
@@ -2,7 +2,7 @@
   "name": "svelte",
   "description": "Cybernetically enhanced web apps",
   "license": "MIT",
-  "version": "5.56.3",
+  "version": "5.56.4",
   "type": "module",
   "types": "./types/index.d.ts",
   "engines": {
@@ -188,7 +188,7 @@
     "clsx": "^2.1.1",
     "devalue": "^5.8.1",
     "esm-env": "^1.2.1",
-    "esrap": "^2.2.11",
+    "esrap": "^2.2.12",
     "is-reference": "^3.0.3",
     "locate-character": "^3.0.0",
     "magic-string": "^0.30.11",
diff --git a/packages/svelte/src/compiler/phases/1-parse/remove_typescript_nodes.js b/packages/svelte/src/compiler/phases/1-parse/remove_typescript_nodes.js
index 438d6fe48f..f573147367 100644
--- a/packages/svelte/src/compiler/phases/1-parse/remove_typescript_nodes.js
+++ b/packages/svelte/src/compiler/phases/1-parse/remove_typescript_nodes.js
@@ -30,6 +30,12 @@ const visitors = {
 		delete n.readonly;
 		delete n.definite;
 		delete n.override;
+
+		// `optional` is reused by JS optional chaining (`a?.b`, `a?.()`), so only
+		// strip the TypeScript optional marker (`x?: T`, `m?(): T`, `x?: T` fields)
+		if (n.type !== 'MemberExpression' && n.type !== 'CallExpression') {
+			delete n.optional;
+		}
 	},
 	Decorator(node) {
 		e.typescript_invalid_feature(node, 'decorators (related TSC proposal is not stage 4 yet)');
diff --git a/packages/svelte/src/internal/client/reactivity/async.js b/packages/svelte/src/internal/client/reactivity/async.js
index 8cb76a9226..91afbee853 100644
--- a/packages/svelte/src/internal/client/reactivity/async.js
+++ b/packages/svelte/src/internal/client/reactivity/async.js
@@ -26,6 +26,7 @@ import {
 	set_reactivity_loss_tracker
 } from './deriveds.js';
 import { aborted } from './effects.js';
+import { queue_micro_task } from '../dom/task.js';
 
 /**
  * @param {Blocker[]} blockers
@@ -173,6 +174,7 @@ export async function save(promise) {
 
 	return () => {
 		restore();
+		queue_micro_task(unset_context);
 		return value;
 	};
 }
diff --git a/packages/svelte/src/version.js b/packages/svelte/src/version.js
index b6d4236ff8..ef468a2f79 100644
--- a/packages/svelte/src/version.js
+++ b/packages/svelte/src/version.js
@@ -4,5 +4,5 @@
  * The current version, as set in package.json.
  * @type {string}
  */
-export const VERSION = '5.56.3';
+export const VERSION = '5.56.4';
 export const PUBLIC_VERSION = '5';
diff --git a/packages/svelte/tests/runtime-runes/samples/async-parallel-derived-template-mutation/_config.js b/packages/svelte/tests/runtime-runes/samples/async-parallel-derived-template-mutation/_config.js
new file mode 100644
index 0000000000..9650e88993
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-parallel-derived-template-mutation/_config.js
@@ -0,0 +1,44 @@
+import { tick } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	mode: ['client'],
+
+	compileOptions: {
+		dev: true
+	},
+
+	async test({ assert, target, errors }) {
+		await tick();
+		const [increment, update, resolve] = target.querySelectorAll('button');
+
+		increment.click();
+		await tick();
+
+		resolve.click();
+		await tick();
+
+		update.click();
+		await tick();
+
+		resolve.click();
+		await tick();
+
+		assert.deepEqual(
+			errors.filter((error) => error.includes('state_unsafe_mutation')),
+			[]
+		);
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<button>increment</button>
+				<button>update</button>
+				<button>resolve</button>
+				<p>count: 1</p>	
+				<p>submits: 1</p>	
+				<p>pending: 0</p>	
+				<p>2</p>	
+			`
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/async-parallel-derived-template-mutation/main.svelte b/packages/svelte/tests/runtime-runes/samples/async-parallel-derived-template-mutation/main.svelte
new file mode 100644
index 0000000000..d9c804b314
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/async-parallel-derived-template-mutation/main.svelte
@@ -0,0 +1,28 @@
+<script>
+	const queued = [];
+
+	function push(value) {
+		if(!value) return value;
+		return new Promise((resolve) => queued.push(() => resolve(value)));
+	}
+
+	let count = $state(0);
+	let submits = $state(0);
+
+	const a = $derived(push(count));
+	const b = $derived(push(count));
+
+	async function updateAfterPromise() {
+		await Promise.resolve(); 
+		submits += 1;
+	}
+</script>
+
+<button onclick={() => (count += 1)}>increment</button>
+<button onclick={updateAfterPromise}>update</button>
+<button onclick={() => queued.shift()?.()}>resolve</button>
+
+<p>count: {count}</p>
+<p>submits: {submits}</p>
+<p>pending: {$effect.pending()}</p>
+<p>{await a + await b}</p>
diff --git a/packages/svelte/tests/snapshot/samples/typescript-optional-parameter/_expected/client/index.svelte.js b/packages/svelte/tests/snapshot/samples/typescript-optional-parameter/_expected/client/index.svelte.js
new file mode 100644
index 0000000000..3593b6c65e
--- /dev/null
+++ b/packages/svelte/tests/snapshot/samples/typescript-optional-parameter/_expected/client/index.svelte.js
@@ -0,0 +1,22 @@
+import 'svelte/internal/disclose-version';
+import 'svelte/internal/flags/legacy';
+import * as $ from 'svelte/internal/client';
+
+export default function Typescript_optional_parameter($$anchor) {
+	// the `?` on the optional parameter must be stripped, but optional chaining
+	// (`x?.length`, `o?.b`) must be preserved
+	function a(x) {
+		return x?.length;
+	}
+
+	const o = {};
+	const v = o?.b?.c;
+
+	a();
+	$.next();
+
+	var text = $.text();
+
+	$.template_effect(() => $.set_text(text, v));
+	$.append($$anchor, text);
+}
\ No newline at end of file
diff --git a/packages/svelte/tests/snapshot/samples/typescript-optional-parameter/_expected/server/index.svelte.js b/packages/svelte/tests/snapshot/samples/typescript-optional-parameter/_expected/server/index.svelte.js
new file mode 100644
index 0000000000..d6c5e271f0
--- /dev/null
+++ b/packages/svelte/tests/snapshot/samples/typescript-optional-parameter/_expected/server/index.svelte.js
@@ -0,0 +1,15 @@
+import * as $ from 'svelte/internal/server';
+
+export default function Typescript_optional_parameter($$renderer) {
+	// the `?` on the optional parameter must be stripped, but optional chaining
+	// (`x?.length`, `o?.b`) must be preserved
+	function a(x) {
+		return x?.length;
+	}
+
+	const o = {};
+	const v = o?.b?.c;
+
+	a();
+	$$renderer.push(`<!---->${$.escape(v)}`);
+}
\ No newline at end of file
diff --git a/packages/svelte/tests/snapshot/samples/typescript-optional-parameter/index.svelte b/packages/svelte/tests/snapshot/samples/typescript-optional-parameter/index.svelte
new file mode 100644
index 0000000000..f6bcb53e47
--- /dev/null
+++ b/packages/svelte/tests/snapshot/samples/typescript-optional-parameter/index.svelte
@@ -0,0 +1,14 @@
+<script lang="ts">
+	// the `?` on the optional parameter must be stripped, but optional chaining
+	// (`x?.length`, `o?.b`) must be preserved
+	function a(x?: string) {
+		return x?.length;
+	}
+
+	const o: { b?: { c: number } } = {};
+	const v = o?.b?.c;
+
+	a();
+</script>
+
+{v}
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index e86c927efe..6331fd0789 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -102,8 +102,8 @@ importers:
         specifier: ^1.2.1
         version: 1.2.1
       esrap:
-        specifier: ^2.2.11
-        version: 2.2.11(@typescript-eslint/types@8.59.4)
+        specifier: ^2.2.12
+        version: 2.2.12(@typescript-eslint/types@8.59.4)
       is-reference:
         specifier: ^3.0.3
         version: 3.0.3
@@ -1418,8 +1418,8 @@ packages:
     resolution: {integrity: sha512-Ap6G0WQwcU/LHsvLwON1fAQX9Zp0A2Y6Y/cJBl9r/JbW90Zyg4/zbG6zzKa2OTALELarYHmKu0GhpM5EO+7T0g==}
     engines: {node: '>=0.10'}
 
-  esrap@2.2.11:
-    resolution: {integrity: sha512-gPdx+I+BjYEinNMQaBXFjbaJVyoPMU4ZODg5mE+M4DqVG9VusAVHHjcBX+zqyITlI0DIARwDMMzZwAWj36dRoQ==}
+  esrap@2.2.12:
+    resolution: {integrity: sha512-On0QbLyaiAkVC4eXtgnXK9Kh2opit+3rcUSOc45DqJ2s/X2eXAHsGOKRSJ6IDagQEW5vPyivANfXUiqgXC67Rw==}
     peerDependencies:
       '@typescript-eslint/types': ^8.2.0
     peerDependenciesMeta:
@@ -2886,7 +2886,7 @@ snapshots:
   '@jridgewell/gen-mapping@0.3.5':
     dependencies:
       '@jridgewell/set-array': 1.2.1
-      '@jridgewell/sourcemap-codec': 1.5.0
+      '@jridgewell/sourcemap-codec': 1.5.5
       '@jridgewell/trace-mapping': 0.3.31
 
   '@jridgewell/remapping@2.3.4':
@@ -3695,7 +3695,7 @@ snapshots:
     dependencies:
       estraverse: 5.3.0
 
-  esrap@2.2.11(@typescript-eslint/types@8.59.4):
+  esrap@2.2.12(@typescript-eslint/types@8.59.4):
     dependencies:
       '@jridgewell/sourcemap-codec': 1.5.5
     optionalDependencies: