Portal cleanup throws if mount was externally cleared (1.x and 2.0.0-beta-14)

[yumemi-thomas]

Describe the bug

Disposing a <Portal> throws if the portal mount was externally cleared before Solid cleanup runs. This reproduces in Solid 1.x and still reproduces on Solid 2 next.

Your Example Website or App

https://stackblitz.com/edit/solidjs-templates-wvzy8wgj?file=src%2FApp.tsx

import { createSignal, Show, flush } from 'solid-js';
import { Portal } from '@solidjs/web';

const externalClearMount = document.createElement('div');
document.body.append(externalClearMount);

export default function App() {
  const [open, setOpen] = createSignal(true);
  const [result, setResult] = createSignal('not run');

  return (
    <main>
      <button
        onClick={() => {
          try {
            externalClearMount.textContent = '';
            setOpen(false);
            flush();
            setResult('disposed without throwing');
          } catch (error) {
            setResult(String(error));
          }
        }}
      >
        clear mount then close portal
      </button>

      <p>{result()}</p>

      <Show when={open()}>
        <Portal mount={externalClearMount}>
          <span>overlay</span>
        </Portal>
      </Show>
    </main>
  );
}

Steps to Reproduce the Bug or Issue

1. Open the StackBlitz repro.
2. Click clear mount then close portal.
3. Observe the rendered result.

NotFoundError: Failed to execute 'removeChild' on 'Node': The node to be removed is not a child of this node.

Expected behavior

If the mount was already externally cleared, dispose() should not throw.

Expected result:

disposed without throwing

Screenshots or Videos

No response

Platform

• OS: macOS
• Browser: Chrome
• Version: Solid 1.x and Solid 2 next

Additional context

Observed in Solid 1.x and on current Solid 2 next at d8921ac1:

• Closing after mount.textContent = "" throws NotFoundError.

This is an edge case involving external DOM mutation, but Portal mount={...} is specifically for rendering into a DOM node outside the normal component tree. Integration hosts, third-party modal containers, tests, or shell apps can realistically empty that container before Solid disposes the Portal.

This appears related to Portal's marker-range cleanup. Cleanup calls removeChild without guarding whether the child is still in the mount.