Messages for this machine that this agent has not read yet.

lmcp-mac#543: with peek=true it is a read and nothing else. It serves what this reader has not ACKNOWLEDGED (a delivered message comes back until agent_ack names it) and writes nothing about the messages; the delivered mark is then written by the acknowledgement. Without peek (every client up to 3.0.420, and a tray's background poll) nothing changes: the same statements, and serving a message stamps it delivered, which is what keeps those clients from getting it twice.

Reads are per agent, so a broadcast to the machine reaches every agent on it instead of the first one to poll swallowing it.

Delivery is at-least-once, not exactly-once: the SELECT and the read-marking INSERT are separate statements under READ COMMITTED, so two concurrent polls by the same agent_id can both return the same message. Nothing is lost; a message can repeat. Coordination messages are idempotent to act on (a second freeze means what the first one meant), so this is left as is rather than paying for SELECT ... FOR UPDATE SKIP LOCKED.