diff --git a/.changeset/old-fireants-allow.md b/.changeset/old-fireants-allow.md
new file mode 100644
index 000000000000..4857a7a7cdad
--- /dev/null
+++ b/.changeset/old-fireants-allow.md
@@ -0,0 +1,5 @@
+---
+'@astrojs/lit': patch
+---
+
+Render DSD attributes based on `shadowRootOptions`
diff --git a/.changeset/yellow-kings-rhyme.md b/.changeset/yellow-kings-rhyme.md
new file mode 100644
index 000000000000..9b0729772841
--- /dev/null
+++ b/.changeset/yellow-kings-rhyme.md
@@ -0,0 +1,6 @@
+---
+'@astrojs/webapi': patch
+'@astrojs/telemetry': patch
+---
+
+Update `undici` to v5.20.0
diff --git a/packages/astro/src/core/cookies/response.ts b/packages/astro/src/core/cookies/response.ts
index d04ce1ef3848..18d72ab1c77b 100644
--- a/packages/astro/src/core/cookies/response.ts
+++ b/packages/astro/src/core/cookies/response.ts
@@ -15,12 +15,14 @@ function getFromResponse(response: Response): AstroCookies | undefined {
 	}
 }
 
-export function* getSetCookiesFromResponse(response: Response): Generator<string, void, unknown> {
+export function* getSetCookiesFromResponse(response: Response): Generator<string, string[]> {
 	const cookies = getFromResponse(response);
 	if (!cookies) {
-		return;
+		return [];
 	}
 	for (const headerValue of cookies.headers()) {
 		yield headerValue;
 	}
+
+	return [];
 }
diff --git a/packages/astro/src/vite-plugin-astro-server/response.ts b/packages/astro/src/vite-plugin-astro-server/response.ts
index 008e7daabdc9..a7cc6e093609 100644
--- a/packages/astro/src/vite-plugin-astro-server/response.ts
+++ b/packages/astro/src/vite-plugin-astro-server/response.ts
@@ -55,19 +55,24 @@ export function writeHtmlResponse(res: http.ServerResponse, statusCode: number,
 export async function writeWebResponse(res: http.ServerResponse, webResponse: Response) {
 	const { status, headers, body } = webResponse;
 
+	// Attach any set-cookie headers added via Astro.cookies.set()
+	const setCookieHeaders = Array.from(getSetCookiesFromResponse(webResponse));
+	setCookieHeaders.forEach((cookie) => {
+		headers.append('set-cookie', cookie);
+	});
+
 	const _headers = Object.fromEntries(headers.entries());
 
 	// Undici 5.20.0+ includes a `getSetCookie` helper that returns an array of all the `set-cookies` headers.
 	// Previously, `headers.entries()` would already have these merged, but it seems like this isn't the case anymore.
-	if ('getSetCookie' in headers && typeof headers.getSetCookie === 'function') {
-		_headers['set-cookie'] = headers.getSetCookie();
+	if (headers.has('set-cookie')) {
+		if ('getSetCookie' in headers && typeof headers.getSetCookie === 'function') {
+			_headers['set-cookie'] = headers.getSetCookie();
+		} else {
+			_headers['set-cookie'] = headers.get('set-cookie')!;
+		}
 	}
 
-	// Attach any set-cookie headers added via Astro.cookies.set()
-	const setCookieHeaders = Array.from(getSetCookiesFromResponse(webResponse));
-	if (setCookieHeaders.length) {
-		res.setHeader('Set-Cookie', setCookieHeaders);
-	}
 	res.writeHead(status, _headers);
 	if (body) {
 		if (Symbol.for('astro.responseBody') in webResponse) {
diff --git a/packages/integrations/lit/server.js b/packages/integrations/lit/server.js
index da571466f498..aa91d1ea8c65 100644
--- a/packages/integrations/lit/server.js
+++ b/packages/integrations/lit/server.js
@@ -62,7 +62,11 @@ function* render(Component, attrs, slots) {
 	yield `>`;
 	const shadowContents = instance.renderShadow({});
 	if (shadowContents !== undefined) {
-		yield '<template shadowroot="open" shadowrootmode="open">';
+		const { mode = 'open', delegatesFocus } = instance.shadowRootOptions ?? {};
+    // `delegatesFocus` is intentionally allowed to coerce to boolean to
+    // match web platform behavior.
+    const delegatesfocusAttr = delegatesFocus ? ' shadowrootdelegatesfocus' : '';
+		yield `<template shadowroot="${mode}" shadowrootmode="${mode}"${delegatesfocusAttr}>`;
 		yield* shadowContents;
 		yield '</template>';
 	}
diff --git a/packages/integrations/lit/test/server.test.js b/packages/integrations/lit/test/server.test.js
index 439c0877da72..af1f99c71162 100644
--- a/packages/integrations/lit/test/server.test.js
+++ b/packages/integrations/lit/test/server.test.js
@@ -83,4 +83,15 @@ describe('renderToStaticMarkup', () => {
 		expect($(tagName).attr('attr1')).to.equal(attr1);
 		expect($(`${tagName} template`).text()).to.contain(`Hello ${prop1}`);
 	});
+
+	it('should render DSD attributes based on shadowRootOptions', async () => {
+		const tagName = 'lit-component';
+		customElements.define(tagName, class extends LitElement {
+			static shadowRootOptions = {...LitElement.shadowRootOptions, delegatesFocus: true};
+		});
+		const render = await renderToStaticMarkup(tagName);
+		expect(render).to.deep.equal({
+			html: `<${tagName}><template shadowroot=\"open\" shadowrootmode=\"open\" shadowrootdelegatesfocus><!--lit-part--><!--/lit-part--></template></${tagName}>`,
+		});
+	});
 });
diff --git a/packages/webapi/package.json b/packages/webapi/package.json
index 82d9ee1095e9..5316909b30fa 100644
--- a/packages/webapi/package.json
+++ b/packages/webapi/package.json
@@ -50,7 +50,7 @@
   "bugs": "https://github.com/withastro/astro/issues",
   "homepage": "https://github.com/withastro/astro/tree/main/packages/webapi#readme",
   "dependencies": {
-    "undici": "5.18.0"
+    "undici": "5.20.0"
   },
   "devDependencies": {
     "@rollup/plugin-alias": "^3.1.9",
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 257e854965ce..fa8b964c1660 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -3678,10 +3678,10 @@ importers:
       rollup: ^2.79.1
       tslib: ^2.4.0
       typescript: ~4.7.3
-      undici: 5.18.0
+      undici: 5.20.0
       urlpattern-polyfill: ^1.0.0-rc5
     dependencies:
-      undici: 5.18.0
+      undici: 5.20.0
     devDependencies:
       '@rollup/plugin-alias': 3.1.9_rollup@2.79.1
       '@rollup/plugin-inject': 4.0.4_rollup@2.79.1
@@ -14871,13 +14871,6 @@ packages:
       jiti: 1.17.0
     dev: false
 
-  /undici/5.18.0:
-    resolution: {integrity: sha512-1iVwbhonhFytNdg0P4PqyIAXbdlVZVebtPDvuM36m66mRw4OGrCm2MYynJv/UENFLdP13J1nPVQzVE2zTs1OeA==}
-    engines: {node: '>=12.18'}
-    dependencies:
-      busboy: 1.6.0
-    dev: false
-
   /undici/5.20.0:
     resolution: {integrity: sha512-J3j60dYzuo6Eevbawwp1sdg16k5Tf768bxYK4TUJRH7cBM4kFCbf3mOnM/0E3vQYXvpxITbbWmBafaDbxLDz3g==}
     engines: {node: '>=12.18'}