Introduce InfoPanel.

InfoPanels are information displays that do not cost actions. One of them (the Prompt) is shown at the main menu; others can be made available as options in the menu, ether on an ongoing basis or for the current/next turn only.

cardsim/infopanel.go

@@ -0,0 +1,13 @@
+package cardsim
+
+// An InfoPanel displays some set of stats to the player. It does
+// not consume an action. It must not advance the state of the game
+// in any way.
+type InfoPanel[C StatsCollection] interface {
+	// Title returns the title of this InfoPanel, which is also used as the
+	// label presented to the player to access this panel.
+	Title(p *Player[C]) (Message, error)
+
+	// Info returns the contents of this InfoPanel.
+	Info(p *Player[C]) ([]Message, error)
+}

cardsim/player.go

@@ -12,8 +12,11 @@ type Player[C StatsCollection] struct {
 	ActionsPerTurn    int
 	ActionsRemaining  int
 	PermanentActions  []Card[C]
+	InfoPanels        []InfoPanel[C]
+	Prompt            InfoPanel[C]
 	Rules             *RuleCollection[C]
 	Rand              rand.Rand
 	Turn              int
-	PendingMessages  []Message
+	TemporaryMessages []Message
+	TemporaryPanels   []InfoPanel[C]
 }