games: the short stack that could win money it never matched

A review pass, and it found the one that would have cost somebody real chips.

Side pots were only ever cut in runout() — the path taken when the betting
stops because nobody is left able to bet. But a hand reaches a showdown with an
all-in player in it and the betting having finished perfectly normally: a short
stack shoves, two players who still have chips behind call, and then keep
betting past them street after street to the river. Nothing was cut. One pot,
everybody eligible, and the short stack takes the lot — every chip the deep
players put in after they were already all-in, money that could never have been
lost to them. All-in for 100 against two players who each put in 500, and the
best hand collects 1,100 instead of the 300 it was playing for.

Chip conservation never saw it. The chips balance perfectly; they just land in
the wrong seat. And every browser session went through runout(), because a
player shoving is what ends the betting. It took reading the code.

Also from the review: play() dereferenced a table it had just been handed as
null, the top-up button offered chips the wallet could not cover, and the
trainer's ETA was sixty thousand hands optimistic on the first line it printed.

Claude-Session: https://claude.ai/code/session_013M5nD7PgUboJXoDcYHzpuJ

internal/games/holdem/eval.go

@@ -78,6 +78,24 @@ func (s *State) showdown(evs *[]Event) {
 	s.collect()
 	s.Street = Showdown
 
+	// Cut the side pots, if nobody has cut them yet.
+	//
+	// runout() does this, but runout only happens when the betting stops because
+	// there is nobody left able to bet. A hand can reach a showdown with an all-in
+	// player in it and the betting having finished perfectly normally: a short stack
+	// shoves, and two players who both have chips behind keep betting past them,
+	// street after street, all the way to the river. Nothing has been cut, and the
+	// short stack is sitting in a single pot marked eligible for all of it.
+	//
+	// Which means they can win every chip the deep players put in *after* they were
+	// already all-in — money they could never have lost. All-in for 100 against two
+	// players who each put in 500, and the best hand takes 1,100 instead of the 300
+	// they were playing for. The chips still balance, so conservation says nothing;
+	// they just go to the wrong seat.
+	if len(s.Side) == 0 && s.anyAllIn() {
+		s.sidePots()
+	}
+
 	// Say so. The last street's bets are still sitting in front of the seats that
 	// made them, as far as the felt knows, and nothing else in the script is going
 	// to tell it they have been swept in.