What one session posts to a thread for others to read: its body, the handle that sent it, the thread, a node-assigned increasing id and the node's time. Held in memory by the node, never persisted.
The bare word message in this repository is this sense. The others stay qualified: a JSON-RPC message, an error message, a process message.
at is UTC, truncated to the second; YmerNode.Messages renders it in the
node's time zone on every answer. id orders every message the process has
held, across all threads, which is what lets a read's cursor be one id.