避免月/年视图切换时整棵树销毁：共存 + Modifier.alpha 控制

Perfetto trace 显示 Compose:onForgotten 耗时 600ms，根因是
if(!isYearView)/if(isYearView) 条件渲染导致整棵子树在切换时被销毁重建。

修复：
1. 月视图和年视图始终共存于组合树中
2. 通过 Modifier.alpha() 控制可见性和触摸事件分发
3. graphicsLayer 仅保留 scale 动画，alpha 移出到 Modifier 层
4. 简化 toggleYearView()：移除 withFrameNanos/animJob.join() 的复杂协程逻辑

两个视图通过 yearViewProgress 驱动的交叉淡入淡出同步切换，
消除 onForgotten 的组件销毁开销。

shared/src/commonMain/kotlin/plus/rua/project/CalendarViewModel.kt

@@ -108,13 +108,12 @@ class CalendarViewModel(
     /**
      * 切换年视图。仅在展开态可用。
      *
-     * 切换瞬间立即翻转 isYearView，让对应方向的目标视图立刻接管渲染，
+     * 月/年视图始终共存于组合树中，由 alpha 控制可见性。
-     * 当前视图被直接移除；动画只作用在目标视图的 scale/alpha 上。
+     * 翻转 isYearView 后启动 Animatable 动画，驱动对应方向视图的 scale/alpha 变化。
      */
     fun toggleYearView() {
         yearViewJob?.cancel()
         yearViewJob = coroutineScope.launch {
-            // 折叠态先展开回月视图，再切换年视图
             if (isCollapsed) {
                 _collapseAnimatable.animateTo(
                     0f, spring(dampingRatio = 0.8f, stiffness = 400f)
@@ -122,32 +121,19 @@ class CalendarViewModel(
                 isCollapsed = false
             }
             if (isYearView) {
-                // 年 → 月：先启动动画（年视图开始淡出），等一帧后翻转 isYearView（月视图开始组合）
+                // 年 → 月：动画驱动 yearViewProgress 1f→0f，月视图同步放大/淡入
-                composeTraceBeginSection("YearView→MonthView")
+                _yearViewAnimatable.animateTo(
-                _yearViewAnimatable.snapTo(1f)
+                    0f, tween(400, easing = FastOutSlowInEasing)
-                val animJob = launch {
+                )
-                    _yearViewAnimatable.animateTo(
-                        0f, tween(400, easing = FastOutSlowInEasing)
-                    )
-                }
-                withFrameNanos { }
                 isYearView = false
-                animJob.join()
-                composeTraceEndSection()
             } else {
-                // 月 → 年：先启动动画（月视图开始缩小），等一帧后翻转 isYearView（年视图开始组合）
+                // 月 → 年：动画驱动 yearViewProgress 0f→1f，年视图同步缩小/淡入
-                composeTraceBeginSection("MonthView→YearView")
                 yearViewYear = selectedDate.year
                 _yearViewAnimatable.snapTo(0f)
-                val animJob = launch {
+                _yearViewAnimatable.animateTo(
-                    _yearViewAnimatable.animateTo(
+                    1f, tween(400, easing = FastOutSlowInEasing)
-                        1f, tween(400, easing = FastOutSlowInEasing)
+                )
-                    )
-                }
-                withFrameNanos { }
                 isYearView = true
-                animJob.join()
-                composeTraceEndSection()
             }
         }
     }

shared/src/commonMain/kotlin/plus/rua/project/ui/CalendarMonthView.kt

@@ -59,8 +59,6 @@ import kotlinx.datetime.number
 import kotlinx.datetime.plus
 import kotlinx.datetime.todayIn
 import plus.rua.project.CalendarViewModel
-import plus.rua.project.composeTraceBeginSection
-import plus.rua.project.composeTraceEndSection
 import kotlin.math.abs
 import kotlin.time.Clock
 
@@ -208,36 +206,33 @@ fun CalendarMonthView(
                 screenHeightPx = size.height
             }
     ) {
-        // 月视图层：仅在非年视图时渲染，年视图激活时立即移除。
+        // 月视图层：始终存在于组合树中，通过 alpha 控制可见性/触摸，避免 isYearView
-        if (!viewModel.isYearView) {
+        // 切换时触发整棵树销毁（Compose:onForgotten 600ms）。scale 动画保留在 graphicsLayer。
-            composeTraceBeginSection("MonthView:Compose")
+        val monthProgress = 1f - viewModel.yearViewProgress
+        val layoutReady = rowHeightPx > 0
+        val monthAlpha = if (layoutReady) monthProgress.coerceIn(0f, 1f) else 0f
+        Box(
+            modifier = Modifier
+                .fillMaxSize()
+                .alpha(monthAlpha)
+                .graphicsLayer {
+                    val scale = lerp(0.3f, 1f, monthProgress)
+                    scaleX = scale
+                    scaleY = scale
+                    transformOrigin = TransformOrigin(anchorPivotX, anchorPivotY)
+                }
+        ) {
             val dragRangeMinPx = with(density) { DRAG_RANGE_MIN_DP.dp.toPx() }
             val dragRangePx = if (effectiveRowHeightPx > 0) {
                 maxOf((effectiveWeeks - 1) * effectiveRowHeightPx.toFloat(), dragRangeMinPx)
             } else {
                 dragRangeMinPx
             }
-
+            Column(
-            val monthProgress = 1f - viewModel.yearViewProgress
-            // 组合阶段计算：lambda 捕获快照值，避免 draw 阶段读到已更新的 rowHeightPx
-            // 但 layout 仍用旧值导致行堆叠
-            val layoutReady = rowHeightPx > 0
-            Box(
                 modifier = Modifier
                     .fillMaxSize()
-                    .graphicsLayer {
+                    .padding(horizontal = HORIZONTAL_PADDING_DP.dp)
-                        val scale = lerp(0.3f, 1f, monthProgress)
-                        scaleX = scale
-                        scaleY = scale
-                        alpha = if (layoutReady) monthProgress.coerceIn(0f, 1f) else 0f
-                        transformOrigin = TransformOrigin(anchorPivotX, anchorPivotY)
-                    }
             ) {
-                Column(
-                    modifier = Modifier
-                        .fillMaxSize()
-                        .padding(horizontal = HORIZONTAL_PADDING_DP.dp)
-                ) {
                     MonthHeader(
                         year = currentYear,
                         month = currentMonth,
@@ -319,25 +314,21 @@ fun CalendarMonthView(
                     )
                 }
             }
-            composeTraceEndSection()
+        // 年视图层：始终存在于组合树中，通过 alpha 控制可见性/触摸。
-        }
+        val yearProgress = viewModel.yearViewProgress
-
+        val yearAlpha = yearProgress.coerceIn(0f, 1f)
-        // 年视图层：标题固定，HorizontalPager 只包裹网格。
+        Column(
-        if (viewModel.isYearView) {
+            modifier = Modifier
-            val yearProgress = viewModel.yearViewProgress
+                .fillMaxSize()
-            composeTraceBeginSection("YearView:Compose")
+                .alpha(yearAlpha)
-            Column(
+                .graphicsLayer {
-                modifier = Modifier
+                    val scale = lerp(3.3f, 1f, yearProgress)
-                    .fillMaxSize()
+                    scaleX = scale
-                    .graphicsLayer {
+                    scaleY = scale
-                        val scale = lerp(3.3f, 1f, yearProgress)
+                    transformOrigin = TransformOrigin(anchorPivotX, anchorPivotY)
-                        scaleX = scale
+                }
-                        scaleY = scale
+                .padding(horizontal = HORIZONTAL_PADDING_DP.dp)
-                        alpha = yearProgress.coerceIn(0f, 1f)
+        ) {
-                        transformOrigin = TransformOrigin(anchorPivotX, anchorPivotY)
-                    }
-                    .padding(horizontal = HORIZONTAL_PADDING_DP.dp)
-            ) {
                 YearHeader(
                     year = viewModel.yearViewYear,
                     onYearChange = { newYear ->
@@ -383,9 +374,6 @@ fun CalendarMonthView(
                     )
                 }
             }
-            composeTraceEndSection()
-        }
-
         // FAB 浮动按钮
         FloatingActionButton(
             onClick = { isMenuExpanded = !isMenuExpanded },