Implement priority token.

internal/game/battle.go

@@ -195,6 +195,18 @@ func (g *Game) resolveBattle() {
 		sides[p.Seat] = s
 		res.StackSizes[p.Seat] = len(p.Deck)
 	}
+	// seatOrder resolves the priority-token holder first, then everyone else.
+	// Reveals, queued play effects, and cross-side triggers all follow it, so
+	// when two pets would act simultaneously (e.g. both throwing rocks) the
+	// holder acts first — its rocks can faint the enemy pet before that pet's
+	// own queued rocks resolve.
+	seatOrder := make([]int, 0, n)
+	seatOrder = append(seatOrder, g.PrioritySeat)
+	for seat := range sides {
+		if seat != g.PrioritySeat {
+			seatOrder = append(seatOrder, seat)
+		}
+	}
 	// Battle-prep effects that start apples in play (Monkey): they attach
 	// to the owner's first pet.
 	for _, p := range g.Players {
@@ -399,7 +411,8 @@ func (g *Game) resolveBattle() {
 		// effects queue up and resolve after all reveals (simultaneous).
 		var plays []queuedPlay
 		newlyPlayed := make([]bool, n)
-		for seat, s := range sides {
+		for _, seat := range seatOrder {
+			s := sides[seat]
 			for s.unit == nil && len(s.stack) > 0 {
 				c := s.stack[0]
 				s.stack = s.stack[1:]
@@ -447,11 +460,12 @@ func (g *Game) resolveBattle() {
 		}
 		// Cross-side play triggers: Rhino rocks anyone who just played;
 		// Crocodile volleys when the enemy plays their last pet.
-		for seat := range sides {
+		for _, seat := range seatOrder {
 			if !newlyPlayed[seat] {
 				continue
 			}
-			for other, os := range sides {
+			for _, other := range seatOrder {
+				os := sides[other]
 				if other == seat {
 					continue
 				}
@@ -644,6 +658,12 @@ func (g *Game) resolveBattle() {
 			res.Trophies = 2
 		}
 		g.Players[winner].Trophies += res.Trophies
+		// Priority token: the winner hands it to the other player; a loser
+		// who held it keeps it; a draw leaves it put. (Two-player rule; the
+		// "other player" is unambiguous only at n == 2.)
+		if winner == g.PrioritySeat {
+			g.PrioritySeat = (winner + 1) % n
+		}
 	}
 
 	g.Battle = res

internal/game/battle_test.go

@@ -20,6 +20,10 @@ func testGame(t *testing.T) (*Game, *Player, *Player) {
 	if g.Phase != PhaseShop {
 		t.Fatalf("expected shop phase after both players join, got %s", g.Phase)
 	}
+	// Pin the (otherwise random) priority token to seat 0 so tests are
+	// deterministic: seat 0 shops first and wins battle simultaneity races.
+	g.PrioritySeat = p1.Seat
+	g.Turn = p1.Seat
 	return g, p1, p2
 }
 
@@ -620,3 +624,75 @@ func TestTemporariesExpireAfterBattle(t *testing.T) {
 		t.Fatalf("pets should survive the round: %+v", p1.Deck)
 	}
 }
+
+// TestPriorityTokenInitialAssignment checks the token starts on a real seat
+// and that seat opens the shop.
+func TestPriorityTokenInitialAssignment(t *testing.T) {
+	g := New()
+	if _, err := g.AddPlayer("Alice"); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := g.AddPlayer("Bob"); err != nil {
+		t.Fatal(err)
+	}
+	if g.PrioritySeat < 0 || g.PrioritySeat >= len(g.Players) {
+		t.Fatalf("priority token should start on a real seat, got %d", g.PrioritySeat)
+	}
+	if g.Turn != g.PrioritySeat {
+		t.Fatalf("priority holder should open the shop: turn=%d priority=%d", g.Turn, g.PrioritySeat)
+	}
+}
+
+// TestPriorityWinsRockRace: two pets that both throw rocks on play would each
+// kill the other, so whoever has priority throws first and survives. Flipping
+// the token flips the winner, proving the token — not seat order — decides.
+func TestPriorityWinsRockRace(t *testing.T) {
+	for _, priority := range []int{0, 1} {
+		g, _, _ := testGame(t)
+		g.RollDie = func() int { return 2 } // 3 dice = 6, lethal to a 2-power pet
+		g.PrioritySeat = priority
+		res := forceBattle(t, g,
+			[]Card{g.realPet(t, "Dolphin")},
+			[]Card{g.realPet(t, "Dolphin")})
+		if res.WinnerSeat != priority {
+			t.Fatalf("priority seat %d should win the rock race, winner=%d", priority, res.WinnerSeat)
+		}
+	}
+}
+
+// TestPriorityTokenTransfer: a winner who holds the token hands it to the
+// loser; a loser who holds it keeps it; a draw leaves it put.
+func TestPriorityTokenTransfer(t *testing.T) {
+	// Winner holds it -> passes to the loser.
+	g, _, _ := testGame(t)
+	g.PrioritySeat = 0
+	forceBattle(t, g, []Card{g.pet("Champ", 9)}, []Card{g.pet("Chump", 1)})
+	if g.Battle.WinnerSeat != 0 {
+		t.Fatalf("seat 0 should win, got %d", g.Battle.WinnerSeat)
+	}
+	if g.PrioritySeat != 1 {
+		t.Fatalf("winner should hand the token to the loser, priority=%d", g.PrioritySeat)
+	}
+
+	// Loser holds it -> keeps it.
+	g, _, _ = testGame(t)
+	g.PrioritySeat = 1
+	forceBattle(t, g, []Card{g.pet("Champ", 9)}, []Card{g.pet("Chump", 1)})
+	if g.Battle.WinnerSeat != 0 {
+		t.Fatalf("seat 0 should win, got %d", g.Battle.WinnerSeat)
+	}
+	if g.PrioritySeat != 1 {
+		t.Fatalf("a losing token holder should keep it, priority=%d", g.PrioritySeat)
+	}
+
+	// Draw -> token stays put. Equal-power pets trade lethal blows at once.
+	g, _, _ = testGame(t)
+	g.PrioritySeat = 0
+	forceBattle(t, g, []Card{g.pet("A", 3)}, []Card{g.pet("B", 3)})
+	if g.Battle.WinnerSeat != -1 {
+		t.Fatalf("mutual KO should draw, got %d", g.Battle.WinnerSeat)
+	}
+	if g.PrioritySeat != 0 {
+		t.Fatalf("a draw should leave the token put, priority=%d", g.PrioritySeat)
+	}
+}

internal/game/game.go

@@ -84,6 +84,11 @@ type Game struct {
 	ShopDecks [][]Card  `json:"shopDecks"` // index 0 = tier 1
 	ShopRow   []Card    `json:"shopRow"`   // empty ID = empty slot
 	Turn      int       `json:"turn"`      // seat with the current shop turn
+	// PrioritySeat holds the priority token: that seat shops first each round
+	// and wins simultaneity races in battle. Assigned randomly at game start;
+	// a battle winner hands it to the loser, a loser keeps it, a draw leaves
+	// it put.
+	PrioritySeat int           `json:"prioritySeat"`
 	Pending      *PendingTrade `json:"pending,omitempty"`
 	Battle       *BattleResult `json:"battle,omitempty"` // most recent battle
 	NextCardID   int           `json:"nextCardId"`
@@ -199,6 +204,8 @@ func (g *Game) PlayerByID(id string) *Player {
 
 func (g *Game) start() {
 	g.Round = 1
+	// The priority token starts with a random seat.
+	g.PrioritySeat = randInt(len(g.Players))
 	g.startShopRound()
 }
 
@@ -216,7 +223,8 @@ func (g *Game) startShopRound() {
 	for i := range g.ShopRow {
 		g.ShopRow[i] = g.drawFromTier(g.Round)
 	}
-	g.Turn = (g.Round - 1) % len(g.Players)
+	// The priority-token holder shops first.
+	g.Turn = g.PrioritySeat
 }
 
 // drawFromTier pops the top card of the given tier's deck (1-based tier).

internal/game/game_test.go

@@ -393,12 +393,17 @@ func TestFullGameFlow(t *testing.T) {
 	g, p1, p2 := testGame(t)
 	p1.Deck = append(p1.Deck, g.pet("Champ", 9))
 	p2.Deck = append(p2.Deck, g.pet("Chump", 1))
+	// testGame pins the priority token to seat 0, and seat 0 wins every
+	// battle, so the token moves to seat 1 after round 1 and stays there (a
+	// loser keeps it). Whoever holds it shops first.
+	wantPriority := p1.Seat
 	for round := 1; round <= MaxRounds; round++ {
 		if g.Round != round || g.Phase != PhaseShop {
 			t.Fatalf("expected shop of round %d, got round %d phase %s", round, g.Round, g.Phase)
 		}
-		if g.Turn != (round-1)%len(g.Players) {
+		if g.PrioritySeat != wantPriority || g.Turn != wantPriority {
-			t.Fatalf("round %d should rotate the starting player, turn=%d", round, g.Turn)
+			t.Fatalf("round %d: priority holder should shop first (want seat %d, priority=%d turn=%d)",
+				round, wantPriority, g.PrioritySeat, g.Turn)
 		}
 		for _, c := range g.ShopRow {
 			if c.ID != "" && c.Tier != round {
@@ -417,6 +422,10 @@ func TestFullGameFlow(t *testing.T) {
 		if g.Battle.WinnerSeat != p1.Seat {
 			t.Fatalf("round %d: seat 0 should win", round)
 		}
+		// The winner hands the token to the loser; a loser keeps it.
+		if wantPriority == g.Battle.WinnerSeat {
+			wantPriority = (wantPriority + 1) % len(g.Players)
+		}
 		for _, p := range g.Players {
 			if err := g.AcknowledgeBattle(p.ID); err != nil {
 				t.Fatal(err)

internal/game/view.go

@@ -25,6 +25,8 @@ type View struct {
 	MaxPets   int    `json:"maxPets"`
 	YouSeat   int    `json:"youSeat"`
 	Turn      int    `json:"turn"`
+	// PrioritySeat is the seat currently holding the priority token.
+	PrioritySeat int          `json:"prioritySeat"`
 	ShopRow      []Card       `json:"shopRow"`
 	DeckCounts   []int        `json:"deckCounts"` // remaining shop cards per tier
 	Players      []PlayerView `json:"players"`
@@ -46,6 +48,7 @@ func (g *Game) ViewFor(playerID string) View {
 		MaxPets:      MaxPets,
 		YouSeat:      -1,
 		Turn:         g.Turn,
+		PrioritySeat: g.PrioritySeat,
 		ShopRow:      g.ShopRow,
 		WinnerSeat:   g.WinnerSeat,
 	}

internal/server/zz_e2e_test.go

@@ -0,0 +1,125 @@
+package server
+
+import (
+	"context"
+	"encoding/json"
+	"net/http/httptest"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/coder/websocket"
+
+	"github.com/greyson/super-auto-pets-board-game/internal/game"
+	"github.com/greyson/super-auto-pets-board-game/internal/store"
+)
+
+func readState(t *testing.T, ctx context.Context, ws *websocket.Conn) *game.View {
+	t.Helper()
+	for {
+		_, data, err := ws.Read(ctx)
+		if err != nil {
+			t.Fatalf("ws read: %v", err)
+		}
+		var m serverMessage
+		if err := json.Unmarshal(data, &m); err != nil {
+			t.Fatalf("unmarshal: %v", err)
+		}
+		if m.Type == "error" {
+			t.Logf("SERVER ERROR: %s", m.Error)
+			continue
+		}
+		if m.Type == "state" && m.State != nil {
+			return m.State
+		}
+	}
+}
+
+func send(t *testing.T, ctx context.Context, ws *websocket.Conn, v any) {
+	t.Helper()
+	data, _ := json.Marshal(v)
+	if err := ws.Write(ctx, websocket.MessageText, data); err != nil {
+		t.Fatalf("ws write: %v", err)
+	}
+}
+
+func TestE2EBattleAckReturnsToShop(t *testing.T) {
+	st, err := store.Open(t.TempDir())
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer st.Close()
+	srv := New(st, "")
+	ts := httptest.NewServer(srv.Handler())
+	defer ts.Close()
+	base := ts.URL
+	wsBase := "ws" + strings.TrimPrefix(base, "http")
+
+	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
+	defer cancel()
+
+	// Directly build a game via the room to control decks, then drive acks
+	// over the wire the way the two browsers do.
+	g := game.New()
+	p1, _ := g.AddPlayer("Alice")
+	p2, _ := g.AddPlayer("Bob")
+	r := &room{game: g, conns: map[*client]struct{}{}}
+	srv.rooms[g.ID] = r
+	if err := st.Save(g); err != nil {
+		t.Fatal(err)
+	}
+
+	dialWS := func(pid, token string) *websocket.Conn {
+		u := wsBase + "/api/ws?game=" + g.ID + "&player=" + pid + "&token=" + token
+		c, _, err := websocket.Dial(ctx, u, nil)
+		if err != nil {
+			t.Fatalf("dial %s: %v", pid, err)
+		}
+		return c
+	}
+	ws1 := dialWS(p1.ID, p1.Token)
+	defer ws1.Close(websocket.StatusNormalClosure, "")
+	ws2 := dialWS(p2.ID, p2.Token)
+	defer ws2.Close(websocket.StatusNormalClosure, "")
+
+	// Force a battle under the lock.
+	r.mu.Lock()
+	g.Players[0].Deck = []game.Card{{ID: "c1", Kind: game.KindPet, Name: "A", Tier: 1, Power: 3, Suit: game.SuitRed}}
+	g.Players[1].Deck = []game.Card{{ID: "c2", Kind: game.KindPet, Name: "B", Tier: 1, Power: 1, Suit: game.SuitRed}}
+	g.Phase = game.PhaseArrange
+	g.Players[0].Ready = false
+	g.Players[1].Ready = false
+	g.SubmitOrder(p1.ID, []string{g.Players[0].Deck[0].ID})
+	g.SubmitOrder(p2.ID, []string{g.Players[1].Deck[0].ID})
+	r.broadcastLocked()
+	r.mu.Unlock()
+
+	readUntilPhase(t, ctx, ws1, game.PhaseBattle)
+	readUntilPhase(t, ctx, ws2, game.PhaseBattle)
+
+	// Both acknowledge.
+	send(t, ctx, ws1, map[string]string{"type": "ready"})
+	send(t, ctx, ws2, map[string]string{"type": "ready"})
+
+	// Each client should eventually observe the shop phase.
+	got1 := readUntilPhase(t, ctx, ws1, game.PhaseShop)
+	got2 := readUntilPhase(t, ctx, ws2, game.PhaseShop)
+	t.Logf("ws1 final phase=%s, ws2 final phase=%s", got1, got2)
+}
+
+func readUntilPhase(t *testing.T, ctx context.Context, ws *websocket.Conn, want game.Phase) game.Phase {
+	t.Helper()
+	deadline := time.Now().Add(3 * time.Second)
+	var last game.Phase
+	for time.Now().Before(deadline) {
+		rctx, cancel := context.WithTimeout(ctx, 2*time.Second)
+		v := readState(t, rctx, ws)
+		cancel()
+		last = v.Phase
+		if v.Phase == want {
+			return v.Phase
+		}
+	}
+	t.Fatalf("never reached %s; last=%s", want, last)
+	return last
+}