Following: Check remote URLs/Objects for Actor type

[pfefferle]

We currently use WebFinger lookup to verify that a remote URL or object is an Actor. This approach is rather lazy and only works because, so far, non-Actor objects don’t include a self link.

Proposed changes:

• Check remote Object for Type Actor

Other information:

• Have you written new tests for your changes, if applicable?

Testing instructions:

• Go to '..'

Changelog entry

• Automatically create a changelog entry from the details below.

Changelog Entry Details

Significance

• Patch
• Minor
• Major

Type

• Added - for new features
• Changed - for changes in existing functionality
• Deprecated - for soon-to-be removed features
• Removed - for now removed features
• Fixed - for any bug fixes
• Security - in case of vulnerabilities

Message

More reliable Actor checks during the follow process.

[Copilot]

Pull Request Overview

This PR improves validation of remote ActivityPub objects by adding a type check to ensure that fetched objects are actually Actors before processing them. The change addresses a gap where the system previously relied solely on WebFinger lookup as proof of Actor type, which was unreliable since non-Actor objects don't typically provide self links.

• Adds explicit Actor type validation using the is_actor() function
• Returns a proper error response when a fetched object is not an Actor type
• Reorganizes import statements for better code organization