it seems like there are some ghost mark types creeping their way into my block content

import {defineMigration, at} from 'sanity/migrate'

const cleanGhostMarks = defineMigration({
  title: 'Clean ghost marks from portable text',
  documentTypes: ['yourDocType'],
  
  migrate: {
    document(doc, context) {
      // Clean your block content field
      if (doc.yourBlockField) {
        return at('yourBlockField', cleanBlockContent(doc.yourBlockField))
      }
    }
  }
})

function cleanBlockContent(blocks) {
  return blocks.map(block => {
    if (block._type !== 'block' || !block.children) return block
    
    const validMarkKeys = new Set(
      (block.markDefs || []).map(def => def._key)
    )
    
    return {
      ...block,
      children: block.children.map(child => ({
        ...child,
        marks: (child.marks || []).filter(mark => 
          validMarkKeys.has(mark) || 
          ['strong', 'em', 'underline', 'code'].includes(mark) // keep decorators
        )
      }))
    }
  })
}

// For @sanity/block-content-to-react (deprecated)
<BlockContent
  blocks={content}
  serializers={{
    marks: {
      // Your existing serializers...
      // These hex IDs will just render as plain text
      'a5a909c5150a': ({children}) => children,
      '80061e4e5eb1': ({children}) => children,
      '1df06a28145f': ({children}) => children,
    }
  }}
/>

// For @portabletext/react (recommended)
<PortableText
  value={content}
  components={{
    marks: {
      // Add serializers for each ghost mark
      'a5a909c5150a': ({children}) => <>{children}</>,
      '80061e4e5eb1': ({children}) => <>{children}</>,
      '1df06a28145f': ({children}) => <>{children}</>,
    }
  }}
/>