feat(mapgen): 生成器序列化 + 世界站位接入（P20 第三步 A）

- MapGen.serialize：生成结果的确定性序列化（尺寸/seed/瓦片/Rivers/Bridges/
  Paths/Buildings），同 seed 逐字节一致，供回归与跨机核对。
- WorldBootstrap.initialWorldWithPlacement：显式站位建世界；旧 64x48 路径
  （initialWorld/initialWorldWithOccupation）字节口径不变。
- WorldBootstrap.initialWorldInMap：用生成器核心可达区做站位，30 spawn 全落
  可达核心；新增 serialization/placement 两条测试。
- fsproj：MapGen 先于 WorldBootstrap 编译。
- Desktop 119->121，Kernel 90 不变。

1 files changed, 29 insertions, 6 deletions

diff --git a/src/LivingVillage.Desktop/WorldBootstrap.fs b/src/LivingVillage.Desktop/WorldBootstrap.fs
index f8ba775..bf0ef65 100644
--- a/src/LivingVillage.Desktop/WorldBootstrap.fs
+++ b/src/LivingVillage.Desktop/WorldBootstrap.fs
@@ -35,17 +35,26 @@ module WorldBootstrap =
                     nowTick
                     state.Today }
 
-    let initialWorldWithOccupation (startAtDaylight: bool) (seed: uint64) (count: int) (occupation: Occupation.State option) : World =
-        if count < 0 || count > npcSpawnTiles.Length then
+    /// 以显式站位建世界：avatarTile 为玩家出生瓦片，npcTiles 为 NPC 出生瓦片序列。
+    /// 64x48 旧档与世界走 `avatarSpawnPosition` + `npcSpawnTiles` 的等价调用，字节口径不变。
+    let initialWorldWithPlacement
+        (startAtDaylight: bool)
+        (seed: uint64)
+        (count: int)
+        (avatarTile: int * int)
+        (npcTiles: (int * int) list)
+        (occupation: Occupation.State option) : World =
+        if count < 0 || count > npcTiles.Length then
             invalidArg (nameof count) "Desktop bootstrap supports at most 30 NPCs."
 
+        let avatarPosition = tileCenter (fst avatarTile) (snd avatarTile)
         let startTick = if startAtDaylight then daylightStartTick else 0L
         let baseWorld = Sim.initialWorldN seed count
         let avatar =
             let baseAvatar =
                 { baseWorld.Avatar with
-                    Pos = avatarSpawnPosition
-                    Mind = { baseWorld.Avatar.Mind with Target = avatarSpawnPosition } }
+                    Pos = avatarPosition
+                    Mind = { baseWorld.Avatar.Mind with Target = avatarPosition } }
             match occupation with
             | None -> baseAvatar
             | Some state ->
@@ -56,11 +65,11 @@ module WorldBootstrap =
                             Needs =
                                 { needs with
                                     Money = float32 state.Profile.InitialMoney
-                                    Energy = state.Profile.InitialEnergy } } }
+                                    Energy = float32 state.Profile.InitialEnergy } } }
         let npcs =
             baseWorld.Npcs
             |> Array.mapi (fun index npc ->
-                let x, y = npcSpawnTiles.[index]
+                let x, y = List.item index npcTiles
                 { npc with Pos = tileCenter x y })
 
         { baseWorld with
@@ -69,6 +78,20 @@ module WorldBootstrap =
             Avatar = avatar
             Npcs = npcs }
 
+    let initialWorldWithOccupation (startAtDaylight: bool) (seed: uint64) (count: int) (occupation: Occupation.State option) : World =
+        initialWorldWithPlacement
+            startAtDaylight
+            seed
+            count
+            (31, 25)
+            (List.ofArray npcSpawnTiles)
+            occupation
+
+    /// P20 第三步：默认可玩世界。生成器的核心可达区作为站位，30 个 spawn 全部落核心可达域。
+    let initialWorldInMap (startAtDaylight: bool) (seed: uint64) (count: int) (map: MapGen.Result) : World =
+        let avatarTile = ((map.Core.MinX + map.Core.MaxX) / 2, (map.Core.MinY + map.Core.MaxY) / 2)
+        initialWorldWithPlacement startAtDaylight seed count avatarTile map.Spawns None
+
     let initialWorldForDaylight (startAtDaylight: bool) (seed: uint64) (count: int) : World =
         initialWorldWithOccupation startAtDaylight seed count None