Handle Follow rejects

[pfefferle]

Implement basic Reject handling.

The focus of this PR is on rejecting Follow requests, but we will add support for other Rejects in the future: https://www.w3.org/wiki/ActivityPub/Primer/Reject_activity#Additional_uses_of_Reject

Proposed changes:

• Handle Follow rejects

Other information:

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

Testing instructions:

• Follow an Account that supports Accepting and Rejecting Follow requests
• Reject Follow request

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

Added basic support for handling remote rejections of follow requests.

[obenland]

This looks really good. I think it'd be optimal to wait with merging until #1839 is in, to avoid making that PR even bigger.

The base branch was changed.

[Copilot]

Pull Request Overview

This PR adds basic support for handling remote Reject activities for follow requests in ActivityPub.

• Introduce a Reject handler to process rejected follow activities and send notifications
• Extend the Following collection with a reject method to clean up pending/following metadata
• Register the new handler hook and include unit tests and a changelog entry

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
tests/includes/handler/class-test-reject.php	Add unit tests covering validation and functional reject flow
includes/handler/class-reject.php	Implement Reject handler with follow-reject logic
includes/collection/class-following.php	Add reject method to remove pending/following metadata
includes/class-handler.php	Register the Reject handler in the main dispatcher
.github/changelog/1865-from-description	Add changelog entry for this feature

Comments suppressed due to low confidence (2)

tests/includes/handler/class-test-reject.php:112

• [nitpick] The test method name implies the user remains in pending after a reject, but the assertions verify removal from pending. Consider renaming to test_handle_reject_removes_user_from_pending for clarity.

	public function test_handle_reject_keeps_user_in_pending() {

tests/includes/handler/class-test-reject.php:164

• The inline comment conflicts with the following assertNotContains check. Update the comment to say Assert: user_id is NOT in _activitypub_followed_by_pending to match the assertion.

		// Assert: user_id is STILL in _activitypub_followed_by_pending.