From what we’ve discussed, I’d map Board AppView onto existing Seed blobs like this:

1. Change Blob

Used for durable decisions made by an actor.

Document change

{
  "type": "Change",
  "objectType": "Document",
  "objectId": "hm://site/doc-login",
  "operation": "EditBlock",
  "payload": {
    "blockId": "block-1",
    "text": "Improve login flow"
  },
  "author": "hm://account/gabo",
  "parents": ["cid-prev-change"],
  "signature": "..."
}

So Board messages become Board change blobs.

2. Ref Blob

Used when one object references another.

Board references a Document

{
  "type": "Ref",
  "source": "hm://site/board-roadmap",
  "target": "hm://other-site/doc-login",
  "relation": "card-document",
  "context": {
    "cardId": "card-login"
  }
}

This says:

This Board represents this Document as a Card.

3. Capability Blob

Used for permissions.

Permission to add cards to a Board

{
  "type": "Capability",
  "resource": "hm://site/board-roadmap",
  "grantee": "hm://account/alice",
  "permissions": [
    "board.view",
    "board.edit",
    "board.addCard",
    "board.positionCard"
  ],
  "issuer": "hm://account/gabo",
  "signature": "..."
}

4. Comment Blob / Discussion Change

If conversations stay on Documents, not Boards:

{
  "type": "Change",
  "objectType": "Document",
  "objectId": "hm://site/doc-login",
  "operation": "AddComment",
  "payload": {
    "anchor": "block-1",
    "text": "Should this move to Review?"
  },
  "author": "hm://account/alice",
  "signature": "..."
}

The Card shows the comment count, but the Board does not own the conversation.

5. Query Blob / Query Change

If Query is an actor, its definition can also be a change blob.

{
  "type": "Change",
  "objectType": "Query",
  "objectId": "hm://site/query-roadmap-descendants",
  "operation": "UpdateDefinition",
  "payload": {
    "rootDocument": "hm://site/project-root",
    "selector": "descendants"
  },
  "author": "hm://account/gabo",
  "signature": "..."
}

Then Board attaches the Query:

{
  "type": "Change",
  "objectType": "Board",
  "objectId": "hm://site/board-roadmap",
  "operation": "AttachQuery",
  "payload": {
    "queryId": "hm://site/query-roadmap-descendants",
    "targetListId": "backlog"
  },
  "author": "hm://account/gabo",
  "signature": "..."
}

6. Blob / Media Blob

Used for card covers or document media.

{
  "type": "Blob",
  "mimeType": "image/png",
  "cid": "bafy-image-cover"
}

Board change:

{
  "type": "Change",
  "objectType": "Board",
  "objectId": "hm://site/board-roadmap",
  "operation": "SetCardCover",
  "payload": {
    "cardId": "card-login",
    "cover": "bafy-image-cover"
  }
}

Clean model

Document edits      → Change blobs
Board operations    → Change blobs
Board-document link → Ref blobs
Permissions         → Capability blobs
Comments            → Document change blobs
Queries             → Query change blobs
Images/files        → Media blobs

So the Board AppView probably needs no new blob type. It needs a new object type, Board, and new change operations for that object.