Feature Request: Add `messages_attachment_fetch` tool

[IGI2]

I've been using iMCP with Claude and noticed that message attachments are referenced in the output (e.g., at_0_F1E5F818-3332-446C-B96B-E60C6ED3F0F7) but there's no way to actually retrieve them.

Use case

When Claude fetches messages, I can see that attachments exist, but I cannot view or process them. This limits the usefulness of the Messages integration – for example, I can't ask Claude to read a document someone sent me via iMessage.

Proposed solution

Add a new tool messages_attachment_fetch that retrieves attachment content:

messages_attachment_fetch:
  - attachment_id: string (required) – the attachment identifier from messages_fetch
  
Returns:
  - data: base64 encoded file content
  - mime_type: string (e.g., "image/jpeg", "application/pdf")
  - filename: string

Technical feasibility

Based on iMessage's SQLite structure:

• attachment table in chat.db contains metadata (file path, MIME type, filename)
• Physical files are stored in ~/Library/Messages/Attachments/
• Relationship: message → message_attachment_join → attachment

Since iMCP already uses Madrid to read chat.db, extending it to query the attachment table should be straightforward.

Sandbox considerations

The user would need to grant access to the ~/Library/Messages/Attachments/ folder via NSOpenPanel, similar to how access to chat.db is currently handled.

Optional enhancements

• Size limit parameter to avoid loading large videos
• Thumbnail generation for images
• List attachments for a specific conversation

Would love to see this feature added!