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。

7 files changed, 38 insertions, 0 deletions

diff --git a/docs/evidence/p74-analysis.txt b/docs/evidence/p74-analysis.txt
new file mode 100644
index 0000000..907a063
--- /dev/null
+++ b/docs/evidence/p74-analysis.txt
@@ -0,0 +1,26 @@
+P74（启动开场过渡：水墨式渐显）证据分析 — 真实 Desktop xvfb 1280x720
+钩子：LV_P74_SHOT=1（60Hz 固定步进，splash 帧表 8/30/60/100/140 各一帧）
+路径：splashFrame → InkReveal.inkStrength/dabs（预乘墨滴）→ 露出天色/水面/屋脊/标题
+
+log shots: 8(ink=0.770), 30(ink=0.325), 60(ink=0.053), 100(ink=0.000), 140(ink=0.000)
+
+p74-splash-008.png: size=1280x720 brightness=46.5 std=25.6 dark_block=0 white_block=405
+p74-splash-030.png: size=1280x720 brightness=51.7 std=38.4 dark_block=0 white_block=232
+p74-splash-060.png: size=1280x720 brightness=56.0 std=48.9 dark_block=0 white_block=232
+p74-splash-100.png: size=1280x720 brightness=56.4 std=49.0 dark_block=0 white_block=232
+p74-splash-140.png: size=1280x720 brightness=56.4 std=49.1 dark_block=0 white_block=232
+
+diff frame 008 vs 030: differing_pixels=670116
+diff frame 008 vs 060: differing_pixels=686287
+diff frame 008 vs 100: differing_pixels=528158
+diff frame 008 vs 140: differing_pixels=537994
+diff frame 030 vs 060: differing_pixels=733221
+diff frame 030 vs 100: differing_pixels=692402
+diff frame 030 vs 140: differing_pixels=702640
+diff frame 060 vs 100: differing_pixels=525583
+diff frame 060 vs 140: differing_pixels=545037
+diff frame 100 vs 140: differing_pixels=120790
+
+verdict=PASS
+  ink strength decays to 0 across the captured frames; frames render 1280x720,
+  no big black/white blocks, and every pair differs (the opening transition animates).
diff --git a/docs/evidence/p74-splash-008.png b/docs/evidence/p74-splash-008.png
new file mode 100644
index 0000000..d0c1a01
--- /dev/null
+++ b/docs/evidence/p74-splash-008.png
diff --git a/docs/evidence/p74-splash-030.png b/docs/evidence/p74-splash-030.png
new file mode 100644
index 0000000..e42ba63
--- /dev/null
+++ b/docs/evidence/p74-splash-030.png
diff --git a/docs/evidence/p74-splash-060.png b/docs/evidence/p74-splash-060.png
new file mode 100644
index 0000000..401c0d4
--- /dev/null
+++ b/docs/evidence/p74-splash-060.png
diff --git a/docs/evidence/p74-splash-100.png b/docs/evidence/p74-splash-100.png
new file mode 100644
index 0000000..bce9efa
--- /dev/null
+++ b/docs/evidence/p74-splash-100.png
diff --git a/docs/evidence/p74-splash-140.png b/docs/evidence/p74-splash-140.png
new file mode 100644
index 0000000..71cef5a
--- /dev/null
+++ b/docs/evidence/p74-splash-140.png
diff --git a/docs/维护说明.md b/docs/维护说明.md
index 9d27dd1..3064e1a 100644
--- a/docs/维护说明.md
+++ b/docs/维护说明.md
@@ -209,6 +209,18 @@ dotnet src/LivingVillage.Headless/bin/Release/net8.0/LivingVillage.Headless.dll
 - 门槛：clean rebuild 0 警告 0 错误；`final_digest=953775FAEB2FDDE97289491AA260BD8D390C571E48A7A13AD2CB6FB7124F7F6C`
   一致、`performance_determinism=PASS`。
 
+## P74 启动开场过渡（水墨式渐显）
+
+- 新增纯函数模块 `InkReveal.fs`：`inkStrength`（起手 1，`dissolveFrames=96` 内 ease-out 退到 0）、
+  `dabs frame width height`（6 滴归一化种子墨滴，随消散半径外扩、alpha 下降）、`inkRgb=(26,36,52)`。
+  单滴 `alpha < 255` 且用 `VillageArt.ellipseRuns` + `premultiply` 落成柔光墨晕，**绝无实心黑块**。
+- 接线：`Game.DrawSplash` 在场景层（天色/云/屋脊/水面/灯笼）之上、标题之下绘制墨滴，与既有
+  `LaunchScreen.revealProgress/veilAlpha` 淡入/暗幕退场叠加，形成可辨识的水墨开场；HUD 结构未动。
+- **回归**：`P74LaunchTransitionTests`（墨幕单调消散且为 0、墨滴确定/随帧变化、alpha<255、
+  半径 < 半屏、`LaunchScreen` 不变量、开始界面三项 开始/读档/退出 + 有档 继续/读档/退出）。
+- **证据**：`LV_P74_SHOT=1`（60Hz 固定步进，splash 帧表 8/30/60/100/140 各一帧）→
+  `scripts/analyze-p74.py` 断言帧号/墨幕非增/无大黑块/两两 pixel diff>0，落 `docs/evidence/p74-*`。
+
 ## P17 批验：场景细节 / 人物动效 / 昼夜光照精修
 
 - ①街边中式细节物：`scripts/make-jiangnan-art.py` 世界图集由 25 格扩到 28 格（新增 slot 25 石灯笼 /