getCollection() throws DataCloneError when Zod transform returns Temporal.PlainDate

Astro Info

Astro                    v7.1.6
Node                     v26.6.0
System                   Linux (x64)
Package Manager          pnpm
Output                   static
Adapter                  none
Integrations             @astrojs/mdx
                         @astrojs/sitemap

Astro fails to load a content collection when a Zod schema transforms a field into a Temporal.PlainDate.

The error originates from Astro's internal use of structuredClone() in updateImageReferencesInData(). Since Temporal.PlainDate is not cloneable in the current Node.js runtime, getCollection() throws a DataCloneError.

While this may ultimately depend on Node's structuredClone implementation, Astro currently doesn't document this limitation, and the failure occurs during normal content loading.

Reproduction
content.config.ts

import { defineCollection, z } from "astro:content";

const posts = defineCollection({
    schema: z.object({
        publishedOn: z
            .string()
            .transform((value) => Temporal.PlainDate.from(value)),
    }),
});

export const collections = {
    posts,
};

src/content/posts/example.md

---
publishedOn: 2026-08-04
---

Code
const posts = await getCollection("posts");

Current behavior

Astro throws:

DataCloneError: [object Temporal.PlainDate] could not be cloned.

    at structuredClone (...)
    at updateImageReferencesInData (...)
    at getCollection (...)

What's the expected result?

Expected behavior

One of the following:

• Astro documents that collection data must be structuredClone-compatible.
• Astro detects unsupported values and throws a more descriptive error.
• If feasible, Astro avoids cloning user-defined objects that do not require modification.