Start a thread

Opens a new conversation in the newsletter's community and returns it. Needs content: write.

The thread is written by the person the credential belongs to, the same person createArticle credits, and readers see it exactly as if they had posted it in Commune. Subscribers are notified the way they are for any new thread, and an @username in the text mentions that person.

content is Markdown, as readers write it in Commune: plain text with light formatting, up to 5,000 characters. It is stored as sent. It can be left out when media attaches something, so a photo with no caption is a thread; a body with neither answers 400.

visibility decides where the thread can be read. subscribers, the default, keeps it inside the newsletter. public also puts it on Commune's global feed in the same write, which is what Put a thread on the global feed (POST /threads/{thread}/publish) does to a thread that already exists.

Publishes thread.created, and thread.published with source created_public when the thread is created public.