In The West Wing, characters use the expression "full lid" to mean that there's no more news for the day:
That's a full lid, folks.
That much is obvious from context, and for the context-impaired, the internet spells it out. In fact, the internet suggests this idiom was invented by the show.
I know what it means, but I really can't make sense of why it means that. Can someone explain the implicit metaphor? What thing from common experience has a lid that becomes filled? And how does fullness represent an ending or hiatus?