feat: auto-save on scene change + resume from auto-save

- useGameEngine: auto-save to slot 0 on every sceneChange event
- useGameEngine: add resumeAutoSave() for continuing from auto-save
- useGameEngine: extract registerEvents() to share between start and resume
- SaveLoadMenu: show slot 0 as '自动存档' with distinct styling and read-only button
- App.vue: check auto-save on load, show '继续上次进度' button if available

src/App.vue

@@ -12,13 +12,15 @@ const videoElB = ref<HTMLVideoElement | null>(null)
 const loading = ref(true)
 const started = ref(false)
 const showMenu = ref(false)
+const hasAutoSave = ref(false)
 
-const { loadGame, start, makeChoice, saveGame, loadGameFromSlot, refreshSaves } =
+const { loadGame, start, resumeAutoSave, makeChoice, saveGame, loadGameFromSlot, refreshSaves, saveSystem } =
   useGameEngine(() => [videoElA.value, videoElB.value])
 
 async function init() {
   await loadGame('/scenes/demo.json')
   loading.value = false
+  hasAutoSave.value = (await saveSystem.load(0)) !== null
 }
 
 function handleStart() {
@@ -26,6 +28,11 @@ function handleStart() {
   start()
 }
 
+async function handleResume() {
+  started.value = true
+  await resumeAutoSave()
+}
+
 function onVideoReady(elA: HTMLVideoElement, elB: HTMLVideoElement) {
   videoElA.value = elA
   videoElB.value = elB
@@ -72,6 +79,7 @@ init()
       </div>
       <div v-if="!started" class="start-overlay">
         <button class="start-btn" @click="handleStart">开始游戏</button>
+        <button v-if="hasAutoSave" class="start-btn resume-btn" @click="handleResume">继续上次进度</button>
       </div>
       <div v-if="store.gameEnded" class="game-end-overlay">
         <div class="game-end-text">游戏结束</div>
@@ -190,4 +198,10 @@ html, body {
 .start-btn:hover {
   background: rgba(255, 255, 255, 0.25);
 }
+
+.resume-btn {
+  margin-top: 16px;
+  border-color: rgba(100, 200, 255, 0.3);
+  color: #8cf;
+}
 </style>

src/components/SaveLoadMenu.vue

@@ -21,6 +21,23 @@ const maxSlots = 5
       <h2 class="save-title">存档 / 读档</h2>
 
       <div class="slot-list">
+        <div class="save-slot auto-save-slot">
+          <div class="slot-label auto-save-label">自动存档</div>
+          <div class="slot-info" v-if="saves.find(s => s.slot === 0)">
+            {{ saves.find(s => s.slot === 0)!.sceneLabel }}
+          </div>
+          <div class="slot-info empty" v-else>暂无自动存档</div>
+          <div class="slot-actions">
+            <button
+              class="slot-btn load-btn"
+              :disabled="!saves.find(s => s.slot === 0)"
+              @click="emit('load', 0)"
+            >
+              读取
+            </button>
+          </div>
+        </div>
+
         <div
           v-for="slot in maxSlots"
           :key="slot"
@@ -94,6 +111,15 @@ const maxSlots = 5
   border-radius: 4px;
 }
 
+.auto-save-slot {
+  border-color: rgba(100, 200, 255, 0.3);
+  background: rgba(100, 200, 255, 0.06);
+}
+
+.auto-save-label {
+  color: #6cf;
+}
+
 .slot-label {
   font-size: 14px;
   color: #aaa;

src/composables/useGameEngine.ts

@@ -20,14 +20,12 @@ export function useGameEngine(videoEls: () => [HTMLVideoElement | null, HTMLVide
     engine.stateManager.init(data.variables)
   }
 
-  function start() {
-    const [elA, elB] = videoEls()
-    engine.videoManager.attach(elA!, elB!)
-
+  function registerEvents() {
     engine.on('sceneChange', (scene) => {
       store.setScene(scene)
       store.clearChoices()
       store.clearTimer()
+      saveGame(0)
     })
 
     engine.on('choiceRequest', (choiceList) => {
@@ -49,10 +47,22 @@ export function useGameEngine(videoEls: () => [HTMLVideoElement | null, HTMLVide
       store.setGameEnded(true)
       engine.choiceSystem.stop()
     })
+  }
 
+  function start() {
+    const [elA, elB] = videoEls()
+    engine.videoManager.attach(elA!, elB!)
+    registerEvents()
     engine.start()
   }
 
+  async function resumeAutoSave(): Promise<boolean> {
+    const [elA, elB] = videoEls()
+    engine.videoManager.attach(elA!, elB!)
+    registerEvents()
+    return await loadGameFromSlot(0)
+  }
+
   function makeChoice(index: number) {
     const scene = store.currentScene
     if (!scene?.choices) return
@@ -99,5 +109,5 @@ export function useGameEngine(videoEls: () => [HTMLVideoElement | null, HTMLVide
     destroy()
   })
 
-  return { loadGame, start, makeChoice, saveGame, loadGameFromSlot, refreshSaves, engine, saveSystem }
+  return { loadGame, start, resumeAutoSave, makeChoice, saveGame, loadGameFromSlot, refreshSaves, engine, saveSystem }
 }