Message body, trimmed. May contain markdown.
1-based end line of this message.
1-based start line in the source note (for jumping to that point).
Speaker role from the message heading.
ISO-8601 timestamp from the heading (writer-supplied, not reparsed).
Parsed message row returned by chatThreadRead.
line_start/line_endare 1-based and let the agent jump to or surgically edit a single turn in the conversation.