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）。

2 files changed, 170 insertions, 63 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
diff --git a/src/LivingVillage.Desktop/VillageArt.fs b/src/LivingVillage.Desktop/VillageArt.fs
index 19c9aa6..3ad5b19 100644
--- a/src/LivingVillage.Desktop/VillageArt.fs
+++ b/src/LivingVillage.Desktop/VillageArt.fs
@@ -600,13 +600,48 @@ module VillageArt =
     let private offsetTile (position: TilePosition) dx dy : TilePosition =
         tilePosition (position.X + dx) (position.Y + dy)
 
+    let private fillRect (spriteBatch: SpriteBatch) (pixel: Texture2D) (color: XnaColor) (x: int) (y: int) (w: int) (h: int) =
+        spriteBatch.Draw(pixel, XnaRectangle(x, y, max 1 w, max 1 h), color)
+
+    /// 生成器世界里的桥面与沿河民居（白墙黑瓦色块 + 门）；坐标由调用方按相机换算。
+    let private drawMapStructures
+        (spriteBatch: SpriteBatch)
+        (textures: ArtTextures)
+        (pixel: Texture2D)
+        (tileX: int -> int)
+        (tileY: int -> int)
+        (cell: int)
+        (map: MapGen.Result) =
+        let bridgeSource = tileSourceRectangle BridgeSprite
+        for (x, y) in map.Bridges do
+            spriteBatch.Draw(textures.TileAtlas, XnaRectangle(tileX x, tileY y, cell, cell), bridgeSource, XnaColor.White)
+        for building in map.Buildings do
+            for row in building.Top .. building.Top + building.Height - 1 do
+                // 白墙朝向道路一行（门所在行），其余为黑瓦屋顶，两侧河岸朝向一致。
+                let color =
+                    if row = building.DoorY then XnaColor(236, 232, 220)
+                    else XnaColor(48, 52, 60)
+                fillRect spriteBatch pixel color (tileX building.Left) (tileY row) (building.Width * cell) (cell)
+            fillRect spriteBatch pixel (XnaColor(96, 60, 42)) (tileX building.DoorX) (tileY building.DoorY) cell cell
+
+    /// 桥头灯笼瓦片：每座桥每列的最上/最下一格（桥两端），用于挂灯笼与夜间暖光。
+    let bridgeLanternTiles (map: MapGen.Result) : (int * int) list =
+        map.Bridges
+        |> List.groupBy fst
+        |> List.collect (fun (x, entries) ->
+            let ys = entries |> List.map snd
+            [ (x, List.min ys); (x, List.max ys) ])
+        |> List.distinct
+
     let drawWorld
         (spriteBatch: SpriteBatch)
         (textures: ArtTextures)
+        (pixel: Texture2D)
         (camera: XnaVector2)
         (viewportWidth: int)
         (viewportHeight: int)
         (plan: JiangnanRenderPlan)
+        (mapGen: MapGen.Result option)
         (tick: int64)
         (tint: XnaColor) =
         let draw position sprite =
@@ -622,26 +657,30 @@ module VillageArt =
 
         // Procedural terrain for the 512x384 large world: water/pebble/peat codes map
         // onto the jiangnan atlas sprites with deterministic ripple continuity.
+        // 生成器世界：1 水 / 2 石板路 / 3 泥炭 / 0 草地。泥炭按草地渲染，路走石板贴图。
         let drawTerrainTile (position: TilePosition) (code: int) =
             match code with
             | 1 -> draw position (waterSpriteAt position)
             | 2 -> draw position StonePathSprite
-            | 3 -> draw position StonePathSprite
             | _ -> draw position GrassSprite
 
         let drawBaseTile (position: TilePosition) =
-            match ProceduralMap.terrainOption, ProceduralMap.bigWorldActive with
-            | (Some terrain, true) ->
-                let tx, ty = position.X, position.Y
-                let code = terrain.Tiles.[ty * ProceduralMap.width + tx]
-                drawTerrainTile position code
-            | _ ->
+            match mapGen with
+            | Some map ->
+                drawTerrainTile position map.Tiles.[position.Y * map.Width + position.X]
+            | None ->
+                match ProceduralMap.terrainOption, ProceduralMap.bigWorldActive with
+                | (Some terrain, true) ->
+                    let tx, ty = position.X, position.Y
+                    let code = terrain.Tiles.[ty * ProceduralMap.width + tx]
+                    drawTerrainTile position code
+                | _ ->
+                    match textures.Cc0TileAtlas with
+                    | Some cc0 -> drawCc0Tile spriteBatch cc0 tint (cc0GroundRect position) (position.X * Sim.tilePixels - int camera.X) (position.Y * Sim.tilePixels - int camera.Y)
+                    | None -> draw position GrassSprite
                 match textures.Cc0TileAtlas with
                 | Some cc0 -> drawCc0Tile spriteBatch cc0 tint (cc0GroundRect position) (position.X * Sim.tilePixels - int camera.X) (position.Y * Sim.tilePixels - int camera.Y)
                 | None -> draw position GrassSprite
-            match textures.Cc0TileAtlas with
-            | Some cc0 -> drawCc0Tile spriteBatch cc0 tint (cc0GroundRect position) (position.X * Sim.tilePixels - int camera.X) (position.Y * Sim.tilePixels - int camera.Y)
-            | None -> draw position GrassSprite
 
         let tx0, ty0, tx1, ty1 =
             MapGen.visibleTileRange Sim.mapWidthTiles Sim.mapHeightTiles (int camera.X) (int camera.Y) viewportWidth viewportHeight
@@ -649,7 +688,19 @@ module VillageArt =
             for x in tx0 .. tx1 do
                 drawBaseTile (tilePosition x y)
 
-        for localPosition, kind in plan.Grounds do
+        // 生成器世界：叠加桥面、沿河民居、桥头灯笼；不再绘制 64x48 样例平面与道具。
+        match mapGen with
+        | Some map ->
+            let mapTileX x = x * Sim.tilePixels - int camera.X
+            let mapTileY y = y * Sim.tilePixels - int camera.Y
+            drawMapStructures spriteBatch textures pixel mapTileX mapTileY Sim.tilePixels map
+            for (lanternX, lanternY) in bridgeLanternTiles map do
+                draw (tilePosition lanternX lanternY) LanternSprite
+        | None -> ()
+
+        // 回退（64x48 样例世界）或 LV_MAP_SCALE 大世界时仍绘制样例地面/道具。
+        let planGrounds = match mapGen with Some _ -> [] | None -> plan.Grounds
+        for localPosition, kind in planGrounds do
             let position = worldTile plan localPosition
             match kind with
             | Water -> draw position (waterSpriteAt position)
@@ -693,7 +744,8 @@ module VillageArt =
         let drawSingleTile localPosition sprite =
             draw (worldTile plan localPosition) sprite
 
-        for prop in plan.Props do
+        let planProps = match mapGen with Some _ -> [] | None -> plan.Props
+        for prop in planProps do
             match prop.Kind with
             | House -> drawHouse prop.Position
             | Bridge -> drawBridge prop.Position
@@ -717,37 +769,13 @@ module VillageArt =
             | 0 -> SmokeSpriteA
             | 1 -> SmokeSpriteB
             | _ -> SmokeSpriteC
-        for prop in plan.Props do
+        for prop in planProps do
             match prop.Kind with
             | House -> draw (offsetTile (worldTile plan prop.Position) 0 -3) smokeSprite
             | _ -> ()
 
     /// P20 证据用：把整张 MapGen 地图等比缩放到视口内绘制，返回绘制的瓦片数。
     /// 仅用于 `LV_MAPGEN_SHOT` 整图取证，不参与正常游戏循环。
-    let private fillRect (spriteBatch: SpriteBatch) (pixel: Texture2D) (color: XnaColor) (x: int) (y: int) (w: int) (h: int) =
-        spriteBatch.Draw(pixel, XnaRectangle(x, y, max 1 w, max 1 h), color)
-
-    /// 整图证据里叠加桥面与沿河民居（白墙黑瓦色块 + 门）。
-    let private drawMapStructures
-        (spriteBatch: SpriteBatch)
-        (textures: ArtTextures)
-        (pixel: Texture2D)
-        (tileX: int -> int)
-        (tileY: int -> int)
-        (cell: int)
-        (map: MapGen.Result) =
-        let bridgeSource = tileSourceRectangle BridgeSprite
-        for (x, y) in map.Bridges do
-            spriteBatch.Draw(textures.TileAtlas, XnaRectangle(tileX x, tileY y, cell, cell), bridgeSource, XnaColor.White)
-        for building in map.Buildings do
-            for row in building.Top .. building.Top + building.Height - 1 do
-                // 白墙朝向道路一行（门所在行），其余为黑瓦屋顶，两侧河岸朝向一致。
-                let color =
-                    if row = building.DoorY then XnaColor(236, 232, 220)
-                    else XnaColor(48, 52, 60)
-                fillRect spriteBatch pixel color (tileX building.Left) (tileY row) (building.Width * cell) (cell)
-            fillRect spriteBatch pixel (XnaColor(96, 60, 42)) (tileX building.DoorX) (tileY building.DoorY) cell cell
-
     let drawMapFitted
         (spriteBatch: SpriteBatch)
         (textures: ArtTextures)
@@ -767,8 +795,7 @@ module VillageArt =
         let spriteOf code =
             match code with
             | 1 -> WaterSprite
-            | 2
-            | 3 -> StonePathSprite
+            | 2 -> StonePathSprite
             | _ -> GrassSprite
         for y in 0 .. map.Height - 1 do
             for x in 0 .. map.Width - 1 do
@@ -799,8 +826,7 @@ module VillageArt =
                 | 0 -> WaterSprite
                 | 1 -> WaterSpriteB
                 | _ -> WaterSpriteC
-            | 2
-            | 3 -> StonePathSprite
+            | 2 -> StonePathSprite
             | _ -> GrassSprite
         let mutable drawn = 0
         for y in y0 .. y1 do