Posts may be submitted with longer content than supplied. We should let the client know when a post was truncated so they can notify the user / handle it more gracefully.
Without this, we're **deleting users' content** without any recourse for them. This is bad, and goes against the "no data loss" principle of Write.as.
New idea for Write.as and WriteFreely: add an endpoint that returns whether or not a post will be truncated, so new clients can handle this situation correctly (like by notifying the user). In the web editor, warn the user before publishing if a post will be truncated, and allow them to continue publishing anyway or cancel. On our existing publishing endpoint, just return `truncated: true` if the post was truncated.
Old implementation idea:
> If a post is created and must be truncated due to a user's subscription level, **save the full text to the database** (within a reasonable limit, i.e. highest plan's limit) but return the truncated content and a `truncated: true` property.