[Bug]Selecting the editor causes the iframe to disappear

[YueXingyu5482]

Initial checklist

• I agree to follow the code of conduct
• I searched issues and discussions and couldn’t find anything (or linked relevant results below)

Affected packages and versions

"@milkdown/core": "^7.3.5",     "@milkdown/preset-commonmark": "^7.3.5",     "@milkdown/preset-gfm": "^7.3.5",     "@milkdown/theme-nord": "^7.3.5",     "@milkdown/utils": "^7.3.5",     "@milkdown/vue": "^7.3.5",     "remark-directive": "^3.0.0",     "vue": "^3.4.15"

Link to runnable example

No response

Steps to reproduce

If the default value in the editor is only iframe, the iframe disappears when the editor is selected
`import { InputRule } from '@milkdown/prose/inputrules'
import { $node, $inputRule, $remark } from "@milkdown/utils"
import directive from 'remark-directive';

const remarkPluginId = "iframe"
const remarkDirective = $remark(remarkPluginId, () => directive)
const iframeNode = $node('iframe', () => ({
group: 'block',
atom: true,
isolating: true,
marks: '',
selectable: true,
draggable: true,
defining: true,
attrs: {
src: { default: null },
},
parseDOM: [{
tag: 'iframe',
getAttrs: (dom) => ({
src: dom.getAttribute('src'),
}),
}],
toDOM: (node) => [
'iframe',
{ ...node.attrs, 'contenteditable': false },
0,
],
parseMarkdown: {
match: (node) => {
return node.type === 'leafDirective' && node.name === 'iframe'
},
runner: (state, node, type) => {
state.addNode(type, { src: node.attributes.src });
},
},
toMarkdown: {
match: (node) => node.type.name === 'iframe',
runner: (state, node) => {
state.addNode('leafDirective', undefined, undefined, {
name: 'iframe',
attributes: { src: node.attrs.src },
});
},
}
}))
const iframeInputRule = $inputRule((ctx) => new InputRule(/::iframe{src="(?[^"]+)?"?}/, (state, match, start, end) => {
const [okay, src = ''] = match;
const { tr } = state;

if (okay) {
    tr.replaceWith(start - 1, end, iframeNode.type(ctx).create({ src }));
}

return tr;

}))
export default [iframeInputRule, iframeNode, remarkDirective]`

Expected behavior

The editor is selected, and the contents of the editor are not affected

Actual behavior

The editor is selected, but the iframe is deleted

Runtime

Chrome

OS

macOS

Build and bundle tools

Vite