From ef81048e238844b729942441541d6dcfe6c8ccca Mon Sep 17 00:00:00 2001
From: Elliott Johnson <hello@ell.iott.dev>
Date: Thu, 15 Jan 2026 09:13:33 -0700
Subject: [PATCH] Merge commit from fork

* fix: Use `devalue.uneval` to serialize `hydratable` keys

* oops
---
 .changeset/tasty-vans-repeat.md                    |  5 +++++
 packages/svelte/src/internal/server/renderer.js    |  3 ++-
 .../samples/hydratable-script-escape/_config.js    | 14 ++++++++++++++
 .../samples/hydratable-script-escape/main.svelte   |  9 +++++++++
 4 files changed, 30 insertions(+), 1 deletion(-)
 create mode 100644 .changeset/tasty-vans-repeat.md
 create mode 100644 packages/svelte/tests/runtime-runes/samples/hydratable-script-escape/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/hydratable-script-escape/main.svelte

diff --git a/.changeset/tasty-vans-repeat.md b/.changeset/tasty-vans-repeat.md
new file mode 100644
index 0000000000..d95e8de7e7
--- /dev/null
+++ b/.changeset/tasty-vans-repeat.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: use `devalue.uneval` to serialize `hydratable` keys
diff --git a/packages/svelte/src/internal/server/renderer.js b/packages/svelte/src/internal/server/renderer.js
index 1ecc90ba1f..82f8025759 100644
--- a/packages/svelte/src/internal/server/renderer.js
+++ b/packages/svelte/src/internal/server/renderer.js
@@ -10,6 +10,7 @@ import { BLOCK_CLOSE, BLOCK_OPEN } from './hydration.js';
 import { attributes } from './index.js';
 import { get_render_context, with_render_context, init_render_context } from './render-context.js';
 import { sha256 } from './crypto.js';
+import * as devalue from 'devalue';
 
 /** @typedef {'head' | 'body'} RendererType */
 /** @typedef {{ [key in RendererType]: string }} AccumulatedContent */
@@ -669,7 +670,7 @@ export class Renderer {
 				for (const p of v.promises) await p;
 			}
 
-			entries.push(`[${JSON.stringify(k)},${v.serialized}]`);
+			entries.push(`[${devalue.uneval(k)},${v.serialized}]`);
 		}
 
 		let prelude = `const h = (window.__svelte ??= {}).h ??= new Map();`;
diff --git a/packages/svelte/tests/runtime-runes/samples/hydratable-script-escape/_config.js b/packages/svelte/tests/runtime-runes/samples/hydratable-script-escape/_config.js
new file mode 100644
index 0000000000..bc51795565
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/hydratable-script-escape/_config.js
@@ -0,0 +1,14 @@
+import { test } from '../../test';
+
+export default test({
+	skip_no_async: true,
+	mode: ['hydrate'],
+
+	props: {
+		key: '</script><script>throw new Error("pwned")</script>'
+	},
+
+	async test() {
+		// this test will fail when evaluating the `head` script if the vulnerability is present
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/hydratable-script-escape/main.svelte b/packages/svelte/tests/runtime-runes/samples/hydratable-script-escape/main.svelte
new file mode 100644
index 0000000000..1327492190
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/hydratable-script-escape/main.svelte
@@ -0,0 +1,9 @@
+<script>
+	import { hydratable } from "svelte";
+
+	const { key } = $props();
+
+	const value = await hydratable(key, () => Promise.resolve('safe'));
+</script>
+
+<p>{value}</p>