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)
+	}
+}

internal/ai/eval.go

@@ -8,6 +8,14 @@ import (
 	"github.com/greyson/super-auto-pets-board-game/internal/game"
 )
 
+// sellPetPenalty converts "persistent pet value destroyed by a sell" into a
+// score penalty (see the sell-candidate logic in shop.go). A pet's keepValue
+// is on the order of 1–5; multiplied by this weight and the future's share of
+// the blend, one junk-pet sell drops a candidate by roughly a tenth of a
+// win-probability point — enough to make keeping a body the default, while
+// still letting a strongly positive rollout justify a genuine reshape.
+const sellPetPenalty = 0.20
+
 // winScore converts a simulated battle outcome to a utility for mySeat:
 // win 1, draw 0.5 (nobody gains ground), loss 0, plus a small margin term.
 //

internal/ai/shop.go

@@ -242,11 +242,27 @@ func (b *Bot) decideShop(v *game.View, mem *Memory) *Action {
 		}
 		return 0
 	})
+	// Selling a pet permanently trades a body for a temporary apple — the
+	// apple's one-battle buff shows up in the rollout, but it vanishes next
+	// round, so the persistent value of the pet is simply destroyed. The
+	// future-value term barely registers this (normFuture squashes small deck
+	// swings), which once let the bot treat "sell my worst pet" as free and
+	// bleed its board down to a single pet over successive shop turns. This
+	// explicit penalty prices the loss back in: it scales with the persistent
+	// worth of the pets sold and with how much the future still matters
+	// (1-alpha), so it bites hardest early and fades to nothing in the final
+	// round, where selling for a decisive last battle is a legitimate play the
+	// rollout can judge on its own.
+	futureWeight := 1 - immediateWeight(v)
 	for k := 1; k <= min(3, len(sellable)); k++ {
 		ids := make([]string, 0, k)
 		nd := slices.Clone(deck)
+		petValueSold := 0.0
 		for _, s := range sellable[:k] {
 			ids = append(ids, s.ID)
+			if s.IsPet() {
+				petValueSold += keepValue(s)
+			}
 			idx := slices.IndexFunc(nd, func(c game.Card) bool { return c.ID == s.ID })
 			nd = slices.Delete(nd, idx, idx+1)
 			nd = append(nd, cx.simApple())
@@ -260,6 +276,7 @@ func (b *Bot) decideShop(v *game.View, mem *Memory) *Action {
 		cands = append(cands, candidate{
 			act:   &Action{Type: "sell", Cards: ids},
 			decks: [][]game.Card{nd},
+			bias:  -sellPetPenalty * futureWeight * petValueSold,
 		})
 	}
 
@@ -297,6 +314,13 @@ func (b *Bot) decideShop(v *game.View, mem *Memory) *Action {
 				base = slices.Delete(base, idx, idx+1)
 				base = cx.applyTemplateShopEffects(base, t, game.TriggerTriple)
 			}
+			// Never bet the whole board on the trade: the reward is the top of
+			// the next tier's deck, which can be a food card (or nothing, if the
+			// deck is spent), so trading away the last pets risks an all-food,
+			// auto-losing deck. Mirror the sell guard and skip such a trade.
+			if !deckHasPet(base) {
+				continue
+			}
 			pool := cx.unseenPool(v.Round + 1)
 			if len(pool) == 0 {
 				pool = game.TierContentsForPack(v.Pack, v.Round+1)