Improve AI to stop selling everything.

internal/ai/ai_test.go

@@ -306,3 +306,62 @@ func TestDecideShopNeverSellsLastPet(t *testing.T) {
 		}
 	}
 }
+
+// TestDecideShopKeepsHealthyBoard guards against the slow-bleed bug: with its
+// coins spent, the bot used to find that turning its worst pet into an apple
+// scored marginally *better* than passing (the apple buffs a survivor for one
+// battle; the permanent loss of a body barely dented the squashed future-value
+// term). Repeated every shop turn, that shed the board down to a single pet and
+// an all-apple hand — an automatic loss, since apples don't carry between
+// rounds. A capable bot facing a beatable opponent must now overwhelmingly
+// prefer keeping its four pets over selling one for a throwaway apple.
+func TestDecideShopKeepsHealthyBoard(t *testing.T) {
+	pet := func(id, name string, tier, power int, suit game.Suit) game.Card {
+		return game.Card{ID: id, Kind: game.KindPet, Name: name, Tier: tier, Power: power, Suit: suit}
+	}
+	v := &game.View{
+		Phase:        game.PhaseShop,
+		Round:        3, // mid-game: future value still carries real weight
+		MaxRounds:    game.MaxRounds,
+		MaxPets:      game.MaxPets,
+		Pack:         game.DefaultPack,
+		YouSeat:      0,
+		Turn:         0,
+		PrioritySeat: 0,
+		DeckCounts:   make([]int, game.MaxRounds+1),
+		Players: []game.PlayerView{
+			{Seat: 0, Coins: 0, PetCount: 4, DeckSize: 4, // coins spent: pass vs sell
+				Deck: []game.Card{
+					pet("p1", "Dog", 3, 3, game.SuitRed),
+					pet("p2", "Sheep", 3, 2, game.SuitBlue),
+					pet("p3", "Ant", 1, 2, game.SuitYellow),
+					pet("p4", "Cricket", 1, 1, game.SuitRed),
+				}},
+			{Seat: 1, PetCount: 4, DeckSize: 4},
+		},
+	}
+	// A comparable opponent, so battles are genuinely competitive — selling is
+	// a real temptation, not a hopeless-position tie-break.
+	mem := &Memory{}
+	mem.Opp.Seat = 1
+	for i, n := range []string{"Dog", "Sheep", "Ant", "Cricket"} {
+		mem.Opp.Known = append(mem.Opp.Known, pet(fmt.Sprintf("o%d", i), n, 3, 3, game.SuitRed))
+	}
+
+	bot := New(1.0) // a capable bot should almost never make this trade
+	passes, sells := 0, 0
+	const iters = 300
+	for range iters {
+		switch bot.decideShop(v, mem).Type {
+		case "pass":
+			passes++
+		case "sell":
+			sells++
+		}
+	}
+	// Keeping the board must dominate: pre-fix this scenario went the other way
+	// (selling outnumbered passing). The generous margin absorbs rollout noise.
+	if passes < 4*sells {
+		t.Errorf("bot sheds a healthy board: pass=%d sell=%d (want pass >> sell)", passes, sells)
+	}
+}