We have two persistence alternatives:

Board-owned Seed document at a reserved hidden path

Store the Board state in one hidden document, for example:

/.seed/board

This document owns the Board query, columns, ordering, and per-card workflow metadata.

Attributes on referenced card documents

Store Board-specific data directly on each document that appears as a card.

For example, each referenced document would carry its own column, priority, labels, assignees, or other Board metadata.

Option 1: Board-owned hidden Seed document

Pros:

One place to load/save Board state.

The Board owns its query, columns, layout, labels, priorities, and card overrides.

Works well when cards come from many different document paths.

Supports multiple Boards cleanly.

Moving a card does not mutate the referenced document.

Board history is separate from document content history.

Cons:

We need a reserved hidden path, for example /.seed/board.

We need to define how the JSON state is encoded in a Seed document.

Option 2: Store Board data as attributes on referenced documents

Pros:

The workflow metadata travels with the document.

It is easy to ask “what Board-like metadata does this document have?”

Cons:

It pollutes normal documents with app-specific Board state.

It becomes awkward when the same document appears on multiple Boards.

Moving a card would create a document change, even though the document content did not change.

Permissions get confusing: editing Board layout would require editing every referenced document.

Loading a Board means reading many document attributes instead of one Board state.

Removing a Board would require cleaning metadata from many documents.

The decisive issue is multiple Boards.

If one document can appear on two Boards, this is ambiguous:

{
  "boardColumn": "review",
  "priority": "High"
}

Which Board does that belong to?

You could namespace it:

{
  "boards": {
    "hm://site/.seed/board": {
      "columnId": "review",
      "priority": "High"
    },
    "hm://site/.seed/roadmap-board": {
      "columnId": "backlog",
      "priority": "Low"
    }
  }
}

But then you are spreading Board state across many documents, which makes loading, deleting, migrating, and permissioning harder.

Recommended model:

/.seed/board
  owns query
  owns columns
  owns per-card board overrides keyed by document id

Referenced documents stay clean:

/design/foo
  owns its own content and metadata only

So the Board render becomes:

Board state + Query results = Board UI