feat(duel): allow swapping main view to opponent's board

- Add a toggle on the picture-in-picture window to swap the big board
  with the mini view of the opponent's field
- Color-coded frame and badge identify whose board is currently shown
  (blue = player 1, orange = player 2)
- Block building and rushing while spectating the opponent's board;
  the PiP then shows your own field instead
- Clarify duel-mode descriptions in lobby and start screen, add hints
  in the multiplayer bar
- Replace previous announcement banners so only one shows at a time

src/App.vue

@@ -10,7 +10,28 @@ import PiPCanvas from '@/components/PiPCanvas.vue'
 import StartScreen from '@/components/StartScreen.vue'
 import TowerPanel from '@/components/TowerPanel.vue'
 import TowerShop from '@/components/TowerShop.vue'
+import { playerColor } from '@/game/config'
 import { store } from '@/game/store'
+import { computed } from 'vue'
+
+/** duel: colored frame + label around the main canvas showing whose board it is */
+const frameStyle = computed(() => {
+  if (!store.mp.active || store.mp.mode !== 'duel') return undefined
+  const viewedOwner = store.mp.viewOpponent ? 1 - store.mp.myId : store.mp.myId
+  return { boxShadow: `0 0 0 4px ${playerColor(viewedOwner)}` }
+})
+
+const badgeText = computed(() => {
+  if (!store.mp.active || store.mp.mode !== 'duel') return ''
+  return store.mp.viewOpponent
+    ? `👁 ${store.mp.peerName} – Ansicht (zum Bauen zurückwechseln)`
+    : '🛡 Deine Basis'
+})
+
+const badgeColor = computed(() => {
+  const viewedOwner = store.mp.viewOpponent ? 1 - store.mp.myId : store.mp.myId
+  return playerColor(viewedOwner)
+})
 </script>
 
 <template>
@@ -21,8 +42,15 @@ import { store } from '@/game/store'
       <Hud />
       <MPBar />
       <div class="canvas-wrap">
-        <div class="canvas-box">
+        <div class="canvas-box" :style="frameStyle">
           <GameCanvas />
+          <div
+            v-if="badgeText"
+            class="board-badge"
+            :style="{ background: badgeColor }"
+          >
+            {{ badgeText }}
+          </div>
           <TowerPanel />
           <ObstaclePanel />
           <PiPCanvas />
@@ -56,5 +84,21 @@ import { store } from '@/game/store'
 }
 .canvas-box {
   position: relative;
+  border-radius: 10px;
+}
+.board-badge {
+  position: absolute;
+  bottom: 8px;
+  left: 50%;
+  transform: translateX(-50%);
+  z-index: 4;
+  color: #10151c;
+  font-size: 11.5px;
+  font-weight: 800;
+  padding: 3px 12px;
+  border-radius: 20px;
+  pointer-events: none;
+  box-shadow: 0 2px 8px rgba(0, 0, 0, 0.4);
+  white-space: nowrap;
 }
 </style>

src/components/GameCanvas.vue

@@ -43,6 +43,8 @@ function onMouseMove(e: MouseEvent): void {
 function handleGameClick(x: number, y: number): void {
   engine.setHover(x, y)
   if (mpgame.active) {
+    // while spectating the opponent's board you cannot build
+    if (store.mp.viewOpponent) return
     const tx = Math.floor(x / TILE)
     const ty = Math.floor(y / TILE)
     if (engine.buildType) {

src/components/LobbyScreen.vue

@@ -5,8 +5,8 @@ import { mpgame } from '@/game/mpgame'
 
 const modeText = computed(() =>
   store.mp.mode === 'coop'
-    ? { icon: '🤝', title: 'Coop', desc: 'Gemeinsame Basis, gemeinsames Gold – gemeinsam gegen 20 Wellen.' }
-    : { icon: '⚔', title: '1v1', desc: 'Jeder verteidigt seine eigene Basis. Rushes schicken Gegner zum Feind.' },
+    ? { icon: '🤝', title: 'Coop', desc: 'Ein gemeinsames Spielfeld: gemeinsames Gold und Leben, 20 Wellen zusammen.' }
+    : { icon: '⚔', title: '1v1', desc: 'Jeder verteidigt sein eigenes Spielfeld (deins ist das große). Den Gegner siehst du live im Mini-Fenster und kannst ihm Rushes schicken!' },
 )
 
 function leave(): void {

src/components/MPBar.vue

@@ -22,10 +22,11 @@ function rush(): void {
         <b>{{ store.mp.peerName }}</b>
         ❤ {{ store.mp.opponentLives }} · 🪙 {{ store.mp.opponentGold }} · 🌊 {{ store.mp.opponentWave }}
       </span>
+      <span class="hint">Großes Feld = deins · Gegner live oben links (⤢ zum Wechseln)</span>
       <button
         class="btn rush"
-        :disabled="store.money < store.mp.rushCost"
-        :title="'Schickt Läufer-Rush auf die Basis des Gegners'"
+        :disabled="store.money < store.mp.rushCost || store.mp.viewOpponent"
+        :title="'Schickt Läufer-Rush auf das Feld des Gegners'"
         @click="rush"
       >
         ⚔ Rush senden · 🪙 {{ store.mp.rushCost }}
@@ -64,6 +65,10 @@ function rush(): void {
 .opp b {
   color: var(--text);
 }
+.hint {
+  color: var(--text-dim);
+  font-size: 12px;
+}
 .btn.rush {
   margin-left: auto;
   background: linear-gradient(180deg, #e0563f, #b93a28);

src/components/PiPCanvas.vue

@@ -1,6 +1,7 @@
 <script setup lang="ts">
 import { onBeforeUnmount, onMounted, ref } from 'vue'
 import { store } from '@/game/store'
+import { engine } from '@/game/engine'
 import { mpgame } from '@/game/mpgame'
 import { H, W } from '@/game/config'
 import { Renderer } from '@/game/render'
@@ -16,8 +17,9 @@ onMounted(() => {
   renderer.setCssSize(W * 0.32, H * 0.32)
   const loop = (): void => {
     if (store.mp.mode === 'duel' && store.screen === 'game') {
-      const remote = mpgame.remoteEngine
-      if (remote) renderer?.render(remote)
+      // while viewing the opponent's board big, the PiP shows your own field
+      const target = store.mp.viewOpponent ? engine : mpgame.remoteEngine
+      if (target) renderer?.render(target)
     }
     raf = requestAnimationFrame(loop)
   }
@@ -29,11 +31,18 @@ onBeforeUnmount(() => {
   renderer?.destroy()
   renderer = null
 })
+
+function toggle(): void {
+  mpgame.toggleView()
+}
 </script>
 
 <template>
   <div v-if="store.mp.mode === 'duel'" class="pip">
-    <div class="pip-label">👁 {{ store.mp.peerName }}</div>
+    <button class="pip-label" title="Ansicht wechseln: großes Spielfeld ↔ Mini-Fenster" @click="toggle">
+      <template v-if="store.mp.viewOpponent">🛡 Dein Feld ⤢</template>
+      <template v-else>👁 {{ store.mp.peerName }} ⤢</template>
+    </button>
     <canvas ref="el" class="pip-canvas" />
   </div>
 </template>
@@ -55,8 +64,13 @@ onBeforeUnmount(() => {
   color: var(--text);
   font-size: 11px;
   font-weight: 700;
-  padding: 2px 8px;
+  padding: 3px 8px;
   align-self: flex-start;
+  cursor: pointer;
+  font-family: inherit;
+}
+.pip-label:hover {
+  border-color: var(--accent);
 }
 .pip-canvas {
   display: block;

src/components/StartScreen.vue

@@ -71,7 +71,13 @@ async function joinRoom(): Promise<void> {
       </div>
       <div class="mp-row">
         <button class="mp-btn coop" @click="createRoom('coop')">🤝 Coop-Raum erstellen</button>
-        <button class="mp-btn duel" @click="createRoom('duel')">⚔ 1v1-Raum erstellen</button>
+        <button
+          class="mp-btn duel"
+          title="Jeder verteidigt sein EIGENES Spielfeld (das große). Das Feld des Gegners siehst du live im Mini-Fenster – und kannst ihm Rushes schicken!"
+          @click="createRoom('duel')"
+        >
+          ⚔ 1v1-Raum erstellen
+        </button>
       </div>
       <div class="mp-row">
         <input

src/game/config.ts

@@ -15,6 +15,13 @@ export const OBSTACLE_COST: Record<'tree' | 'rock', number> = {
   rock: 40,
 }
 
+/** multiplayer player identity colors (blue = player 1, orange = player 2) */
+export const PLAYER_COLORS: [string, string] = ['#4da3ff', '#ffb14d']
+
+export function playerColor(playerId: number | null): string {
+  return playerId === null || playerId === 0 ? PLAYER_COLORS[0] : PLAYER_COLORS[1]
+}
+
 /** ground path in tile coords; -1/20 are outside the grid (spawn/exit) */
 export const MAP_WAYPOINTS: [number, number][] = [
   [-1, 5],

src/game/engine.ts

@@ -41,6 +41,8 @@ import { Renderer } from './render'
 /** implemented by the multiplayer controller (mpgame.ts) */
 export interface MPController {
   frame(dtReal: number): void
+  /** engine whose board is shown on the main canvas (view swap in duel mode) */
+  mainView(): GameEngine
 }
 
 interface SpawnEntry {
@@ -357,7 +359,7 @@ export class GameEngine {
       // multiplayer lockstep: the controller advances both engines in sync ticks
       this.mpController.frame(dtReal)
       this.syncStore()
-      this.renderer?.render(this)
+      this.renderer?.render(this.mpController.mainView())
       return
     }
     const active = store.screen === 'game' && !this.paused
@@ -1041,6 +1043,8 @@ export class GameEngine {
   }
 
   announce(str: string, sub: string): void {
+    // only one banner at a time – replaces any previous announcement
+    this.effects = this.effects.filter((fx) => fx.type !== 'announce')
     this.fx({ type: 'announce', str, sub, life: 1.8, max: 1.8 })
   }
 

src/game/mpgame.ts

@@ -172,7 +172,11 @@ class MpGameController {
       remote.mpMode = 'duel'
       remote.localPlayerId = 1 - info.you
       remote.ghost = true
+      // CRITICAL: index boards by PLAYER ID so engines[from] is always the
+      // board owned by the acting player on every client
       this.engines = [engine, remote]
+      this.engines[info.you] = engine
+      this.engines[1 - info.you] = remote
       this.remoteEngine = remote
     }
 
@@ -190,13 +194,33 @@ class MpGameController {
     this.net.remoteTick = -1
     if (this.heartbeat) clearInterval(this.heartbeat)
     this.heartbeat = setInterval(() => this.net.sendProgress(this.myTick), 100)
+    store.mp.viewOpponent = false
 
     engine.announce(
       info.mode === 'coop' ? 'Coop-Modus!' : '1v1-Duell!',
-      info.mode === 'coop' ? 'Gemeinsames Gold – Teamwork!' : 'Verteidige deine Basis!',
+      info.mode === 'coop'
+        ? 'Gemeinsames Gold – Teamwork!'
+        : 'Dies ist DEIN Feld – Gegner live im Mini-Fenster',
     )
   }
 
+  /** duel: is the opponent's board currently shown on the main canvas? */
+  get viewSwap(): boolean {
+    return store.mp.viewOpponent && this.mode === 'duel' && this.remoteEngine !== null
+  }
+
+  /** engine whose board is rendered on the big canvas */
+  mainView(): GameEngine {
+    return this.viewSwap && this.remoteEngine ? this.remoteEngine : engine
+  }
+
+  toggleView(): void {
+    if (this.mode === 'duel' && this.remoteEngine) {
+      store.mp.viewOpponent = !store.mp.viewOpponent
+      engine.cancelMode()
+    }
+  }
+
   private disposeGame(): void {
     if (this.heartbeat) clearInterval(this.heartbeat)
     this.heartbeat = null

src/game/render.ts

@@ -1,4 +1,4 @@
-import { ENEMIES, H, TILE, TOWERS, W } from './config'
+import { ENEMIES, H, TILE, TOWERS, W, playerColor } from './config'
 import type { GameEngine } from './engine'
 import type { Enemy, Tower } from './types'
 import { mulberry32 } from './utils'
@@ -342,7 +342,7 @@ export class Renderer {
     g.lineTo(x + 10, y + 26)
     g.closePath()
     g.fill()
-    // banner
+    // banner carries the owner's color in duel mode (blue/orange)
     g.strokeStyle = '#5b4a35'
     g.lineWidth = 3
     g.beginPath()
@@ -350,7 +350,7 @@ export class Renderer {
     g.lineTo(x, y - 62)
     g.stroke()
     const wave = Math.sin(eng.time * 4) * 3
-    g.fillStyle = '#d84b3f'
+    g.fillStyle = eng.mpMode === 'duel' ? playerColor(eng.localPlayerId) : '#d84b3f'
     g.beginPath()
     g.moveTo(x + 1, y - 62)
     g.lineTo(x + 22 + wave, y - 56)

src/game/store.ts

@@ -54,6 +54,8 @@ export const store = reactive({
     opponentWave: 0,
     rushCost: 0,
     resultMsg: '',
+    /** duel: show the opponent's board on the main canvas */
+    viewOpponent: false,
   },
 })
 

src/main.ts

@@ -1,5 +1,12 @@
 import { createApp } from 'vue'
 import App from './App.vue'
+import { store } from '@/game/store'
+import { mpgame } from '@/game/mpgame'
 import './style.css'
 
+// diagnostic hook (read-only debugging from devtools/automation)
+if (typeof window !== 'undefined') {
+  ;(window as unknown as Record<string, unknown>).__trxtd = { store, mpgame }
+}
+
 createApp(App).mount('#app')