[Bug]: imageService: { build: "compile" } overrides user-configured custom image service

Astro Info

Astro                    v6.1.3
Vite                     v7.3.1
Node                     v25.8.2
System                   macOS (x64)
Package Manager          npm
Output                   static
Adapter                  @astrojs/cloudflare (v13.1.7)
Integrations             none

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

N/A (build-time issue)

Describe the Bug

When using @astrojs/cloudflare with imageService: { build: "compile" } and a custom image service configured in astro.config.ts, the adapter silently replaces the custom service with its own @astrojs/cloudflare/image-service-workerd. The custom service's getURL() and getHTMLAttributes() methods are never called.

In setImageConfig() (image-config.js), the "compile" case unconditionally overrides the image service:

case "compile":
  return {
    ...config,
    service: WORKERD_IMAGE_SERVICE,  // always overrides user's service
    endpoint: ...
  };

Additionally, in prerenderer.js, collectStaticImages hardcodes astro/assets/services/sharp for build-time image transforms:

const { default: sharpService } = await import("astro/assets/services/sharp");
globalThis.astroAsset.imageService = sharpService;

This means there is no way to use a custom image transform pipeline (e.g. an external image CDN or optimization service) with build: "compile".

Reproduction

This repo has a custom image service at src/image-service.ts that returns /cdn/-prefixed URLs and adds a data-image-service="custom" attribute. Neither appears in the build output.

The config:

export default defineConfig({
  output: "static",
  adapter: cloudflare({
    imageService: { build: "compile" },
  }),
  image: {
    service: {
      entrypoint: "./src/image-service.ts",
    },
  },
});

Run npm run build and inspect dist/client/index.html.

What's the expected result?

The custom image service should be used for URL generation and HTML attributes. The rendered HTML should contain:

<img src="/cdn/..." data-image-service="custom" alt="test" width="100" height="100">

---

Potential fix

The "compile" case in setImageConfig should respect the user's image.service configuration instead of unconditionally replacing it. If the user has configured a custom service, it should be used for getURL() and getHTMLAttributes() — the adapter should only fall back to @astrojs/cloudflare/image-service-workerd when no custom service is set.

Similarly, collectStaticImages in prerenderer.js should check whether a custom image service is configured before defaulting to sharp. A "custom" build service option (or detecting that image.service was explicitly set) could skip the sharp override and let the user's transform logic handle image generation.

Link to Minimal Reproducible Example

https://github.com/adamchal/cloudflare-custom-image

Participation

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