fix: guard attachShadow call for SSR DOMs without native support

[tysoncung]

Problem

When using Stencil's hydrate runtime with server-side DOM implementations that don't provide attachShadow (e.g., Domino used by Angular SSR), the hydration process crashes with:

TypeError: this.attachShadow is not a function
    at createShadowRoot ...
    at proxyHostElement ...

This affects Angular SSR + Ionic applications where @angular/ssr uses Domino as its DOM implementation.

Fix

Added a typeof guard in createShadowRoot() (src/utils/shadow-root.ts) that checks whether attachShadow is available on the host element before calling it. When it's missing (SSR environments), the function returns early, allowing hydration to continue without crashing.

This is a minimal, safe change — in browser environments attachShadow is always available so the guard is never hit. In SSR environments, the shadow root simply isn't created, which matches the expected SSR behavior (shadow roots are typically handled during client-side hydration).

Call path

proxyHostElement() → createShadowRoot.call(elm, cmpMeta) → this.attachShadow(opts) 💥

After fix: this.attachShadow checked first → early return if missing → no crash.

Fixes #6605

[johnjenkins]

Hey @tysoncung thanks for raising
But I don’t think this will help really. It will just cause the components to fail silently (as opposed to noisily)

[tysoncung]

Thanks for the feedback! Good point - silently skipping isn't ideal.

What would be the preferred approach here? A few options I can think of:

1. Polyfill attachShadow on the server side so components still get a shadow root
2. Use a declarative shadow DOM approach for SSR contexts
3. Something else entirely?

Happy to rework this based on the team's direction.

[johnjenkins]

You’re an ai agent, right?
attachShadow is already polyfilled in Stencil’s usual server DOM solution.
The issue is with Domino (whose last update was 6 years ago).

I wonder if there’s an opportunity for users to patch Domino before attempting to SSR components.

Take a look at some example code at https://github.com/ionic-team/ionic-framework/blob/main/packages/angular-server/src/ionic-server-module.ts is there a potential call site users can use to patch Domino (the underlying Angular DOM implementation)?
Post your code here.