The "chat-timeline-user" setting:

If this setting is defined and is not an empty string, then timeline events are posted to the chat as they arrive. The synthesized chat messages appear to come from the user identified by this setting, not the user on the timeline event.

All chat messages that come from the chat-timeline-user are interpreted as text/x-fossil-wiki instead of as text/markdown. For this reason, the chat-timeline-user name should probably not be a real user.