feat(mapgen): 默认可玩世界接入生成器 + 河景细节（P20 第三步 B）

- Game：默认 256x192 生成器世界（核心可达区站位），LV_LEGACY_MAP=1 /
  LV_MAP_SCALE>1 / LV_MAP_TOUR=1 回退旧路径；StartNewGame 走同一站位。
- VillageArt.drawWorld 新增 pixel 与 mapGen option：Some 时按生成器瓦片绘地面
  并叠加桥面/沿河民居/门，跳过 64x48 样例平面与道具；水波沿用 waterFrameTickAt。
- 新增 bridgeLanternTiles；夜间 LanternGlow 沿用既有预乘同心圆（无过曝白芯），
  生成器世界用桥头灯笼。
- 新增 LV_RIVERSCAPE_TOUR 真走位巡游与 LV_RECORD_NAME 录屏前缀（证据用）。

1 files changed, 103 insertions, 22 deletions

diff --git a/src/LivingVillage.Desktop/Game.fs b/src/LivingVillage.Desktop/Game.fs
index 5d2ba54..8eafd26 100644
--- a/src/LivingVillage.Desktop/Game.fs
+++ b/src/LivingVillage.Desktop/Game.fs
@@ -126,6 +126,39 @@ type LivingVillageGame() as this =
     let mutable cjkAtlas = Unchecked.defaultof<Texture2D>
     let mutable pixel = Unchecked.defaultof<Texture2D>
     let renderPlan = VillageArt.sampleRenderPlan ()
+    let legacyMapMode = Environment.GetEnvironmentVariable("LV_LEGACY_MAP") = "1"
+    let mapScale =
+        match Environment.GetEnvironmentVariable("LV_MAP_SCALE") with
+        | null | "" -> 1
+        | v -> match Int32.TryParse v with (true, value) -> max 1 value | _ -> 1
+    let mapTourMode = Environment.GetEnvironmentVariable("LV_MAP_TOUR") = "1"
+    // P20 第三步：默认可玩世界走 256x192 生成器（核心可达区站位）；LV_LEGACY_MAP=1 回退 64x48。
+    let riverscapeActive = not legacyMapMode && not mapTourMode && mapScale <= 1
+    let riverscapeMap : MapGen.Result option =
+        if riverscapeActive then
+            Sim.configureBounds 256 192
+            Some (MapGen.generateWithSize 256 192 42UL)
+        else
+            None
+    let riverscapeTourMode = Environment.GetEnvironmentVariable("LV_RIVERSCAPE_TOUR") = "1" && riverscapeActive
+    /// 巡游路点：第一座桥的整列（含两端外沿）+ 民居门 + 核心中心，用于桥面行走取证。
+    let riverscapeTourWaypoints () : (int * int) list =
+        match riverscapeMap with
+        | None -> []
+        | Some map ->
+            let bridgeStops =
+                map.Bridges
+                |> List.groupBy fst
+                |> List.sortBy fst
+                |> List.truncate 1
+                |> List.collect (fun (x, entries) ->
+                    let ys = entries |> List.map snd |> List.sort
+                    [ (x, List.min ys - 2) ] @ [ for y in ys -> (x, y) ] @ [ (x, List.max ys + 2) ])
+            let doors = map.Buildings |> List.map (fun building -> (building.DoorX, building.DoorY))
+            let core = ((map.Core.MinX + map.Core.MaxX) / 2, (map.Core.MinY + map.Core.MaxY) / 2)
+            (bridgeStops @ doors @ [ core ])
+            |> List.filter (fun (x, y) -> x >= 0 && x < map.Width && y >= 0 && y < map.Height)
+            |> List.distinct
     // Evidence hook: pin the starting wall-clock hour (e.g. 20.75 for 黄昏), desktop-only.
     let startHourOverride =
         match Environment.GetEnvironmentVariable("LV_AUTOPLAY_START_HOUR") with
@@ -141,9 +174,20 @@ type LivingVillageGame() as this =
     let withStartTick (world: World) : World =
         let tick = evidenceStartTick ()
         { world with Tick = tick; Time = float tick * Sim.dtSeconds }
+    let initialWorldForMode (occupation: Occupation.State option) : World =
+        match riverscapeMap with
+        | Some map ->
+            let core = map.Core
+            WorldBootstrap.initialWorldWithPlacement
+                daylightAutoplay
+                42UL
+                Sim.npcCount
+                ((core.MinX + core.MaxX) / 2, (core.MinY + core.MaxY) / 2)
+                map.Spawns
+                occupation
+        | None -> WorldBootstrap.initialWorldWithOccupation daylightAutoplay 42UL Sim.npcCount occupation
     let createInitialWorld () =
-        WorldBootstrap.initialWorldForDaylight daylightAutoplay 42UL Sim.npcCount
-        |> withStartTick
+        initialWorldForMode None |> withStartTick
     let mutable world = createInitialWorld ()
     let mutable camera = Vector2.Zero
     let mutable avatarFacing = VillageArt.SouthFacing
@@ -179,11 +223,10 @@ type LivingVillageGame() as this =
         | null | "" -> 25
         | v -> match Int32.TryParse v with (true, value) -> max 1 value | _ -> 25)
     let mutable recordIndex = 0
-    let mutable scale = int (
-        match Environment.GetEnvironmentVariable("LV_MAP_SCALE") with
-        | null | "" -> 1
-        | v -> match Int32.TryParse v with (true, value) -> max 1 value | _ -> 1)
-    let mapTourMode = Environment.GetEnvironmentVariable("LV_MAP_TOUR") = "1"
+    let recordName =
+        match Environment.GetEnvironmentVariable("LV_RECORD_NAME") with
+        | null | "" -> "rec-frame-"
+        | v -> v
     let mutable tourWaypoints =
         [ (1, 1); (255, 191); (509, 381); (256, 60); (256, 300); (80, 200); (430, 300) ]
     let mutable tourIndex = 0
@@ -206,8 +249,8 @@ type LivingVillageGame() as this =
     let mutable mapGenGenMs = 0.0
 
     do
-        if scale > 1 then
-            Sim.configureBounds (64 * scale) (48 * scale)
+        if mapScale > 1 then
+            Sim.configureBounds (64 * mapScale) (48 * mapScale)
             ProceduralMap.activate (uint64 4242)
         if mapGenShotMode then
             let stopwatch = System.Diagnostics.Stopwatch.StartNew()
@@ -229,6 +272,8 @@ type LivingVillageGame() as this =
                 [ (1, 1); (Sim.mapWidthTiles / 2, Sim.mapHeightTiles / 2); (Sim.mapWidthTiles - 3, Sim.mapHeightTiles - 3)
                   (Sim.mapWidthTiles / 2, 60); (Sim.mapWidthTiles / 2, Sim.mapHeightTiles - 60)
                   (80, 200); (430, 300) ]
+        if riverscapeTourMode then
+            tourWaypoints <- riverscapeTourWaypoints ()
         graphics.PreferredBackBufferWidth <- 1280
         graphics.PreferredBackBufferHeight <- 720
         graphics.SynchronizeWithVerticalRetrace <- true
@@ -262,7 +307,7 @@ type LivingVillageGame() as this =
             occupation
             |> Option.map (fun kind -> WorldBootstrap.occupationStateFor 42UL kind startTick)
         world <-
-            WorldBootstrap.initialWorldWithOccupation daylightAutoplay 42UL Sim.npcCount state
+            initialWorldForMode state
             |> withStartTick
         this.ResetWorldView()
         m5View <- { m5View with Task = state }
@@ -372,6 +417,31 @@ type LivingVillageGame() as this =
         if menuShotFrame = MenuShotScript.downFrame then
             this.DispatchMenuInput Down
 
+    /// P20 第三步取证：真走位巡游（Sim.step 驱动）沿桥/路/民居门移动，用于桥面行走帧与昼夜录制。
+    member private this.RunRiverscapeTour () =
+        let target = tourWaypoints.[tourIndex % tourWaypoints.Length]
+        let targetPos : Vec2 =
+            { X = float32 (fst target * Sim.tilePixels + Sim.tilePixels / 2)
+              Y = float32 (snd target * Sim.tilePixels + Sim.tilePixels / 2) }
+        let dx = targetPos.X - world.Avatar.Pos.X
+        let dy = targetPos.Y - world.Avatar.Pos.Y
+        let distance = sqrt (dx * dx + dy * dy)
+        if distance < 3.0f then
+            tourIndex <- tourIndex + 1
+            if tourIndex >= tourWaypoints.Length then
+                printfn "riverscape tour=complete frames=%d" recordIndex
+                this.Exit()
+        else
+            let inv = 1.0f / distance
+            let input = { Input = { MoveX = dx * inv; MoveY = dy * inv } }
+            let before = world.Avatar.Pos
+            world <- Sim.step input world
+            avatarFacing <- VillageArt.facingAfterMovement before world.Avatar.Pos avatarFacing
+            avatarMoving <- distance > 4.0f
+        m5View <- M5Interaction.refreshPrompt world m5View
+        this.CenterCamera()
+        tourFrame <- tourFrame + 1
+
     member private this.RunMapTour () =
         let (tileX, tileY) = tourWaypoints.[tourIndex % tourWaypoints.Length]
         let position : Vec2 =
@@ -396,7 +466,9 @@ type LivingVillageGame() as this =
                 printfn $"map tour={tourIndex} at tile=({tileX},{tileY})"
 
     member private this.UpdatePlaying (gameTime: GameTime) (kb: KeyboardState) (pressed: Keys -> bool) (pressedAny: Keys list -> bool) =
-        if mapTourMode then
+        if riverscapeTourMode then
+            this.RunRiverscapeTour()
+        elif mapTourMode then
             this.RunMapTour()
         elif sampleMode then
             this.RunSampleMode()
@@ -778,7 +850,7 @@ type LivingVillageGame() as this =
                 recordIndex <- recordIndex + 1
                 if recordIndex % recordEvery = 0 then
                     System.IO.Directory.CreateDirectory recordDirectory |> ignore
-                    this.SaveBackBuffer(sprintf "%s/rec-frame-%04d.png" recordDirectory recordIndex)
+                    this.SaveBackBuffer(sprintf "%s/%s%04d.png" recordDirectory recordName recordIndex)
             if menuShotMode then
                 this.CaptureMenuShot()
 
@@ -966,29 +1038,38 @@ type LivingVillageGame() as this =
             VillageArt.drawWorld
                 spriteBatch
                 artTextures
+                pixel
                 camera
                 viewport.Width
                 viewport.Height
                 renderPlan
+                riverscapeMap
                 world.Tick
                 profile.WorldTint
 
             // Warm lantern glows strengthen as night falls (pure function of tick phase).
             // Concentric premultiplied circles fall off radially from each lantern tile, so
             // the core stays a soft warm disc instead of saturating into a white block, and
-            // no glow is painted where there is no lantern entity.
+            // no glow is painted where there is no lantern entity. 生成器世界用桥头灯笼。
             if profile.LanternGlow > 0.3f then
                 let glow = profile.LanternGlow
                 let peakAlpha = int (140.0f * glow)
-                for prop in renderPlan.Props do
-                    match prop.Kind with
-                    | VillageArt.RenderPropKind.RiverLantern ->
-                        let position = VillageArt.worldTile renderPlan prop.Position
-                        let centerX = position.X * Sim.tilePixels - int camera.X + Sim.tilePixels / 2
-                        let centerY = position.Y * Sim.tilePixels - int camera.Y + Sim.tilePixels / 2
-                        for (rect, color) in VillageArt.lanternGlowLayers centerX centerY 44 6 255 214 150 peakAlpha do
-                            spriteBatch.Draw(pixel, rect, color)
-                    | _ -> ()
+                let lanternTiles =
+                    match riverscapeMap with
+                    | Some map -> VillageArt.bridgeLanternTiles map
+                    | None ->
+                        renderPlan.Props
+                        |> List.choose (fun prop ->
+                            match prop.Kind with
+                            | VillageArt.RenderPropKind.RiverLantern ->
+                                let position = VillageArt.worldTile renderPlan prop.Position
+                                Some(position.X, position.Y)
+                            | _ -> None)
+                for (tileX, tileY) in lanternTiles do
+                    let centerX = tileX * Sim.tilePixels - int camera.X + Sim.tilePixels / 2
+                    let centerY = tileY * Sim.tilePixels - int camera.Y + Sim.tilePixels / 2
+                    for (rect, color) in VillageArt.lanternGlowLayers centerX centerY 44 6 255 214 150 peakAlpha do
+                        spriteBatch.Draw(pixel, rect, color)
 
             VillageArt.drawGroundShadow spriteBatch pixel camera world.Avatar.Pos
             let avatarSpec = VillageArt.avatarSpriteSpec avatarFacing avatarMoving world.Tick