implement player loses on move timer expires

Fixes #11.

game.go

@@ -72,6 +72,7 @@ func gameActor(ctx context.Context, g *game.Match, dealer, chall person, join <-
 	dl := time.Now().Add(timeLimit)
 	broadcast(ctx, g, dealer, chall, obs, dl)
 	tick := time.NewTicker(timeLimit)
+	defer tick.Stop()
 	for {
 		select {
 		case <-ctx.Done():
@@ -120,7 +121,9 @@ func gameActor(ctx context.Context, g *game.Match, dealer, chall person, join <-
 			tick.Reset(timeLimit)
 		case <-tick.C:
 			slog.InfoContext(ctx, "out of time")
-			// TODO(zeph): current player concedes
+			g.Expire()
+			gameOver(ctx, dealer, chall, obs)
+			return
 		}
 		// Clear observers who have left.
 		for k := len(obs) - 1; k >= 0; k-- {

game/game.go

@@ -240,6 +240,11 @@ func (g *Match) Concede(id player.ID) error {
 	return ErrRoundEnded
 }
 
+// Expire makes the current player concede.
+func (g *Match) Expire() {
+	g.Concede(g.CurrentPlayer().id)
+}
+
 // DTO returns the current match state as viewed by the given player and with
 // the given deadline on the current player's next move.
 func (g *Match) DTO(id player.ID, deadline time.Time) serve.Game {