Chat lines don't say which line they reply to #874

What happens

In the web and mobile apps, a chat line can be a reply to an earlier line: the UI shows the quoted line above the new one. The CLI has no way to tell that a line is a reply, or which line it answers.

• basecamp chat line <id> --json returns content, title, parent (the chat transcript), creator and so on, but no field pointing at the quoted line. content is only the new text.
• basecamp chat messages --json is the same.
• basecamp events <id> --json shows the created event with details: {}.
• The live event feed (chat.line.created over the events stream) carries the same empty details.

So a tool (or an agent) reading the chat sees a short line like "Let's make it less robotic." with no idea which message it refers to, while a person in the app sees the quote right above it.

What I'd like

The id of the quoted line (and ideally its URL) on a chat line that is a reply, for example:

{
  "id": 222,
  "type": "Chat::Lines::RichText",
  "content": "<p>Let's make it less robotic.</p>",
  "reply_to": { "id": 111, "app_url": "https://app.basecamp.com/…/chats/…@111" }
}

and the same id in the chat.line.created event's details, so a watcher knows without a second request. A basecamp chat reply <line> "<text>" to post a real reply would round it out.

Why

An agent that answers in chat needs to know what a reply is about. Today it has to guess from context, or ask, or the person has to paste the line's link by hand (which does come through, as a link in content). Comments already expose this kind of thing (comments show has reply_target); chat lines don't.

Version

basecamp CLI 0.11.0, macOS. Checked against a real reply in a project chat.