p74: 启动开场过渡（水墨式渐显）+ 开始界面布局回归

新增纯函数 InkReveal.fs（inkStrength ease-out 消散 + 6 滴预乘墨滴 dabs），DrawSplash 在场景层之上、标题之下绘制，与既有 reveal/veil 淡入叠加，形成可辨识水墨开场；单滴 alpha<255 且椭圆行落成，无实心黑块。开始界面沿用既有 开始/读档/退出（有档 继续）。新增 P74LaunchTransitionTests（4 例）与 LV_P74_SHOT/-analyze-p74 证据（5 帧墨幕非增、两两 diff>0，verdict=PASS）。HUD 结构未动；Desktop 350/350、Kernel 120/120、digest 与 p70 一致。

2 files changed, 60 insertions, 0 deletions

diff --git a/src/LivingVillage.Desktop.Tests/LivingVillage.Desktop.Tests.fsproj b/src/LivingVillage.Desktop.Tests/LivingVillage.Desktop.Tests.fsproj
index 11a1b90..fb7ecb7 100644
--- a/src/LivingVillage.Desktop.Tests/LivingVillage.Desktop.Tests.fsproj
+++ b/src/LivingVillage.Desktop.Tests/LivingVillage.Desktop.Tests.fsproj
@@ -45,6 +45,7 @@
     <Compile Include="P71ApiDocsTests.fs" />
     <Compile Include="P72CharacterWalkTests.fs" />
     <Compile Include="P73LightingTierTests.fs" />
+    <Compile Include="P74LaunchTransitionTests.fs" />
     <Compile Include="SampleTests.fs" />
   </ItemGroup>
 
diff --git a/src/LivingVillage.Desktop.Tests/P74LaunchTransitionTests.fs b/src/LivingVillage.Desktop.Tests/P74LaunchTransitionTests.fs
new file mode 100644
index 0000000..880f33b
--- /dev/null
+++ b/src/LivingVillage.Desktop.Tests/P74LaunchTransitionTests.fs
@@ -0,0 +1,59 @@
+namespace LivingVillage.Desktop.Tests
+
+open Microsoft.VisualStudio.TestTools.UnitTesting
+open LivingVillage.Desktop
+open LivingVillage.Kernel
+open LivingVillage.Kernel.Sim
+
+/// P74 回归：启动开场过渡（水墨渐显）纯函数性质 + 开始界面布局入口。
+[<TestClass>]
+type P74LaunchTransitionTests () =
+
+    let width = 1280
+    let height = 720
+
+    [<TestMethod>]
+    member _.InkRevealDissolvesMonotonicallyAndStaysSoft () =
+        // 起手满墨、96 帧后散尽，且整体强度随帧非增（确定性 ease-out）。
+        Assert.AreEqual<float32>(1.0f, InkReveal.inkStrength 0L)
+        Assert.AreEqual<float32>(0.0f, InkReveal.inkStrength InkReveal.dissolveFrames)
+        Assert.AreEqual<float32>(0.0f, InkReveal.inkStrength 140L)
+        let strengths = [ 0L; 8L; 30L; 60L; 95L ] |> List.map InkReveal.inkStrength
+        Assert.AreEqual<float32 list>(strengths, strengths |> List.sortDescending)
+        // 墨滴始终存在、均在画布内、alpha < 255（柔和墨晕，非实心黑块）、半径不覆盖半屏。
+        for frame in [ 0L; 8L; 30L; 60L; 95L ] do
+            let dabs = InkReveal.dabs frame width height
+            Assert.IsTrue(dabs.Length > 0, "墨滴集合不得为空")
+            for dab in dabs do
+                Assert.IsTrue(dab.Alpha >= 0 && dab.Alpha < 255, sprintf "alpha %d 越界" dab.Alpha)
+                Assert.IsTrue(dab.Rx > 0 && dab.Rx < width / 2, "Rx 覆盖过半屏")
+                Assert.IsTrue(dab.Ry > 0 && dab.Ry < height / 2, "Ry 覆盖过半屏")
+
+    [<TestMethod>]
+    member _.InkRevealDabsChangeOverTheTransition () =
+        // 同一帧两次调用一致（确定性）；不同帧墨滴布局不同（动画在变）。
+        Assert.AreEqual<InkReveal.Dab list>(InkReveal.dabs 20L width height, InkReveal.dabs 20L width height)
+        Assert.AreNotEqual<InkReveal.Dab list>(InkReveal.dabs 8L width height, InkReveal.dabs 60L width height)
+
+    [<TestMethod>]
+    member _.LaunchScreenTransitionIsDeterministic () =
+        Assert.AreEqual<float32>(0.0f, LaunchScreen.revealProgress 0L)
+        Assert.AreEqual<float32>(1.0f, LaunchScreen.revealProgress LaunchScreen.fadeInFrames)
+        Assert.AreEqual<float32>(1.0f, LaunchScreen.veilAlpha 0L)
+        Assert.AreEqual<float32>(0.0f, LaunchScreen.veilAlpha LaunchScreen.durationFrames)
+        Assert.IsTrue(LaunchScreen.isComplete LaunchScreen.durationFrames)
+        Assert.IsFalse(LaunchScreen.isComplete (LaunchScreen.durationFrames - 1L))
+        Assert.AreEqual<string>("江南水乡", LaunchScreen.title)
+
+    [<TestMethod>]
+    member _.StartMenuLayoutExposesStartLoadExit () =
+        // 开场结束后的可交互开始界面：无存档 → 开始/读档/退出。
+        let fresh = MenuState.create { Paused = false; Speed = OneX } false
+        Assert.AreEqual<MenuPage>(MainMenu, fresh.Page)
+        Assert.AreEqual<MenuItem list>([ NewGameItem; LoadItem; ExitItem ], MenuState.items fresh)
+        let labels = MenuState.items fresh |> List.map MenuState.itemLabel
+        Assert.AreEqual<string list>([ "开始"; "读档"; "退出" ], labels)
+        // 有进行中的世界 → 继续/读档/退出。
+        let resumed = MenuState.create { Paused = false; Speed = OneX } true
+        Assert.AreEqual<MenuItem list>([ ContinueItem; LoadItem; ExitItem ], MenuState.items resumed)
+        Assert.AreEqual<string>("继续", MenuState.itemLabel (MenuState.selectedItem resumed))