Fix server islands endpoint missing in static Vercel builds

[astrobot-houston]

Changes

• Fixes server:defer components returning 404 responses on Vercel when using output: "static".
• Preserves a dedicated server build directory and packages it through the existing Vercel serverless and middleware path only when Astro runs the SSR build for discovered server islands. Fully static sites continue to emit no serverless function, and server build files are not published as static assets.

Closes #17678

Testing

• Adds a static server-islands fixture that verifies _render.func, its route configuration, and rendering through the packaged function.
• Verifies the server entry is excluded from static assets and a fully static fixture does not create a serverless function.

Docs

• No docs update needed because this restores the documented server:defer behavior for static output.

[changeset-bot]

🦋 Changeset detected

Latest commit: 47495cc

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 22 packages

Name	Type
@astrojs/vercel	Patch
@test/astro-vercel-basic	Patch
@test/astro-vercel-image	Patch
@test/astro-vercel-integration-assets	Patch
@test/vercel-isr	Patch
@test/vercel-max-duration	Patch
@test/vercel-edge-middleware-with-edge-file	Patch
@test/vercel-edge-middleware-without-edge-file	Patch
@test/astro-vercel-no-output	Patch
@test/astro-vercel-prerendered-error-pages	Patch
@test/astro-vercel-redirects-serverless	Patch
@test/astro-vercel-redirects	Patch
@test/vercel-server-islands-static	Patch
@test/vercel-server-islands	Patch
@test/astro-vercel-serverless-prerender	Patch
@test/astro-vercel-serverless-with-dynamic-routes	Patch
@test/astro-vercel-static-assets	Patch
@test/vercel-static-headers	Patch
@test/astro-vercel-static	Patch
@test/vercel-streaming	Patch
@test/astro-vercel-with-web-analytics-enabled-output-as-static	Patch
vercel-hosted-astro-project	Patch

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[matthewp]

Not sure about this one, doesn't appear to relate to server islands very much.

[johanneskvamme]

Not sure about this one, doesn't appear to relate to server islands very much.

Could you elaborate?

I have not evaluated (nor even looked at) the code proposed by the LLM, but my issue of server islands on an Astro project with no on-demand rendered pages 404s on Vercel is resolved by this. I did indeed test it on both a dummy project (my MRE) and my real project. That issue is server island specific, no? Or have I misunderstood?

Whether this is a good or even the right solution is something I can't tell, but it did fix the issue 😊

[matthewp]

Implementation doesn't seem right, doesn't actually detect server islands at all. Seems to build the static entrypoint always. So fixes your issue yes, but probably in the wrong way. I'll dig into it more.

[johanneskvamme]

Implementation doesn't seem right, doesn't actually detect server islands at all. Seems to build the static entrypoint always. So fixes your issue yes, but probably in the wrong way. I'll dig into it more.

Oh, okay, I see. Thanks!

[pkg-pr-new]

npm i https://pkg.pr.new/@astrojs/vercel@17680

commit: 47495cc

[matthewp]

@johanneskvamme can you try out the preview shown above 👆 It's a completely different implementation from what you tried before. Thanks!

[johanneskvamme]

@johanneskvamme can you try out the preview shown above 👆 It's a completely different implementation from what you tried before. Thanks!

@matthewp Thank you for the quick response! I have tested both on the MRE and my actual project, and server island seems to resolve nicely in Vercel with the new fix too 🙌