Astro 6 beta error when building with the "cloudflare:workers" import - Unsupported ESM URL scheme

[rakeshpai]

Astro Info

Astro                    v6.0.0-beta.7
Node                     v24.6.0
System                   macOS (arm64)
Package Manager          pnpm
Output                   static
Adapter                  @astrojs/cloudflare
Integrations             @astrojs/react

If this issue only occurs in one browser, which browser is a problem?

No response

Describe the Bug

When trying to build my Astro 6-beta project which uses Cloudflare workers, I get the following error at the end of the build when prerendering:

<snip>
11:15:50 [types] Generated 3.60s
11:15:50 [build] output: "static"
11:15:50 [build] mode: "server"
11:15:50 [build] directory: /<snip>/<project-dir>/dist/
11:15:50 [build] adapter: @astrojs/cloudflare
11:15:50 [build] Collecting build info...
11:15:50 [build] ✓ Completed in 3.64s.
11:15:50 [build] Building server entrypoints...
Using vars defined in .env
11:15:51 [vite] ✓ built in 1.66s
11:15:52 [vite] ✓ built in 609ms
11:15:55 [vite] ✓ built in 3.00s
11:15:55 [build] ✓ Completed in 5.31s.

 prerendering static routes 
11:15:55 ▶ src/pages/index.astro
11:15:55   └─ /index.html11:15:55 [ERROR] Error [ERR_UNSUPPORTED_ESM_URL_SCHEME]: Only URLs with a scheme in: file, data, and node are supported by the default ESM loader. Received protocol 'cloudflare:'
    at throwIfUnsupportedURLScheme (node:internal/modules/esm/load:183:11)
    at defaultLoad (node:internal/modules/esm/load:78:3)
    at nextLoad (node:internal/modules/esm/hooks:748:28)
    at Hooks.load (node:internal/modules/esm/hooks:385:26)
    at handleMessage (node:internal/modules/esm/worker:201:24)
    at checkForMessages (node:internal/modules/esm/worker:143:28)
    at process.<anonymous> (node:internal/modules/esm/worker:162:5)
    at process.emit (node:events:508:28)
11:15:55 [ERROR] [build] Caught error rendering /: Error: Only URLs with a scheme in: file, data, and node are supported by the default ESM loader. Received protocol 'cloudflare:'
Only URLs with a scheme in: file, data, and node are supported by the default ESM loader. Received protocol 'cloudflare:'
  Stack trace:
    at throwIfUnsupportedURLScheme (node:internal/modules/esm/load:183:11)
    at nextLoad (node:internal/modules/esm/hooks:748:28)
    at handleMessage (node:internal/modules/esm/worker:201:24)
    at process.<anonymous> (node:internal/modules/esm/worker:162:5)
 ELIFECYCLE  Command failed with exit code 1.

I am indeed using import { env } from "cloudflare:workers"; in my code.

My astro config is as follows:

export default defineConfig({
	adapter: cloudflare({
		imageService: "cloudflare",
	}),
	// ...

I don't think the imageService has any bearing on this error, but otherwise it's just a vanilla astro config using the cloudflare adapter.

In trying to create a minimal reproduction of the error, I ran into a similar but different error - this time, the dev server itself throws an error saying:

 astro  v6.0.0-beta.6 ready in 1187 ms

┃ Local    http://localhost:4321/
┃ Network  use --host to expose

▶ This is a  beta  prerelease build!
  Report issues here: https://astro.build/issues

11:18:33 watching for file changes...
11:18:36 [ERROR] Could not import `cloudflare:workers`.
  Hint:
    This is often caused by a typo in the import path. Please make sure the file exists.
  Error reference:
    https://docs.astro.build/en/reference/errors/failed-to-load-module-ssr/
  Stack trace:
    at /<snip>/astro-6-cf-build/src/pages/index.astro:4:21
    [...] See full stack trace in the browser, or rerun with --verbose.

What's the expected result?

importing "cloudflare:workers" should work

Link to Minimal Reproducible Example

https://github.com/rakeshpai/astro-6-cf-build

Participation

• I am willing to submit a pull request for this issue.

[florian-lefebvre]

If you think this is worth addressing, please opena new issue