feat(perf): LV_PERF_SOAK_SECONDS 让 64x48/sample 世界也能长时帧率采样（P22）

- sample 脚本跑完一轮后若未到 soak 秒数则回到开头继续，用于与 256x192
  巡游做同口径的解锁帧率对比；默认 0 行为不变。

1 files changed, 18 insertions, 2 deletions

diff --git a/src/LivingVillage.Desktop/Game.fs b/src/LivingVillage.Desktop/Game.fs
index 28c86db..4305cb6 100644
--- a/src/LivingVillage.Desktop/Game.fs
+++ b/src/LivingVillage.Desktop/Game.fs
@@ -209,6 +209,16 @@ type LivingVillageGame() as this =
     let mutable fpsSamples: float list = []
     let mutable fpsFrames = 0
     let mutable fpsSeconds = 0.0
+    // P22：让 sample/legacy 世界也能长时间采样帧率（>0 时跑完一轮脚本后回到开头继续）。
+    let perfSoakSeconds =
+        match Environment.GetEnvironmentVariable("LV_PERF_SOAK_SECONDS") with
+        | null | "" -> 0.0
+        | v ->
+            match Double.TryParse(v, Globalization.NumberStyles.Float, Globalization.CultureInfo.InvariantCulture) with
+            | true, seconds when seconds > 0.0 -> seconds
+            | _ -> 0.0
+    let perfSoakWatch = System.Diagnostics.Stopwatch()
+    let mutable perfSoakStarted = false
     let mutable prevKb = Unchecked.defaultof<KeyboardState>
     let mutable relationView = false
     let mutable relationSnapshot: float32[,] option = None
@@ -419,6 +429,9 @@ type LivingVillageGame() as this =
         | None -> ()
 
     member private this.RunSampleMode () =
+        if perfSoakSeconds > 0.0 && not perfSoakStarted then
+            perfSoakStarted <- true
+            perfSoakWatch.Start()
         let stageBefore = sampleState.Stage
         let positionBefore = world.Avatar.Pos
         let nextWorld, nextView, nextState = SampleScript.runFrame world m5View sampleState
@@ -432,8 +445,11 @@ type LivingVillageGame() as this =
         if nextState.Stage <> stageBefore then
             printfn $"sample stage={nextState.Stage} tick={nextWorld.Tick} pos=({nextWorld.Avatar.Pos.X:F0},{nextWorld.Avatar.Pos.Y:F0})"
             if nextState.Stage = SampleScript.SampleComplete then
-                printfn (if nextState.TimedOut then "sample result=timeout" else "sample result=ok")
-                this.Exit()
+                if perfSoakSeconds > 0.0 && perfSoakWatch.Elapsed.TotalSeconds < perfSoakSeconds then
+                    sampleState <- SampleScript.initial
+                else
+                    printfn (if nextState.TimedOut then "sample result=timeout" else "sample result=ok")
+                    this.Exit()
 
     /// P16-FIX：菜单截图模式。停在开始界面，按确定性帧表向下切到「读档」，帧表见 MenuShotScript。
     member private this.RunMenuShot () =