Comment replies via Federation: @mention in Federated reply is wrapped in a paragraph

[jeherve]

Quick summary

This is a follow-up to #844, and its fix #1086. The added @mention works well, but for some reason a paragraph is added around the mention, breaking the mention into its own line.

Here is an example:

• Reply on my site: https://herve.bzh/20250107-15467/#comment-173
• Reply on the Fediverse, including a line break: https://mastodon.social/@inkican/113789796331971211
• ActivityPub representation including the line break: https://herve.bzh/?c=173&activitypub
  <p><a class="u-mention mention" href="https://mastodon.social/@inkican">@[email protected]</a></p><p>I&rsquo;ll add it to my « To read » list, thank you! 🙂</p>

Steps to reproduce

1. Publish a post
2. Have another comment reply to the post on the Fediverse
3. On your site, reply to the comment via Federation
4. View the reply in the Fediverse client

What you expected to happen

I would expect the reply to include a @mention of the person I'm replying to, immediately followed by my reply.

What actually happened

Instead the @mention is followed by a line break.

Impact

All

Available workarounds?

There is no user impact

Logs or notes

No response

[github-actions]

This issue could use some more labels, to help prioritize and categorize our work. Could you please add at least a [Type], a [Feature], and a [Pri] label?

[NiceGuy2065]

I can confirm the bug, previously mentioned (with another example in the wild) in #1124.

Thanks @jeherve!