fix(mapgen): 大图关闭孤立装饰石块，杜绝草地上游离石板 tile（P25）

- 新增 Params.DecorativeStones（默认 true）；paramsForSize 对 >256x192 关闭，
  512x384 不再产生 292 个孤立石板（stone 非路网计数归零，石块全部属于路网）。
- 64x48/256x192 保持开启，checksum 6042052/1284656962 不变。
- 新增 NoIsolatedStoneTiles / DecorativeStonesDisabledOnLargeMaps 回归；Desktop 134 -> 136。

1 files changed, 31 insertions, 0 deletions

diff --git a/src/LivingVillage.Desktop.Tests/MapGenTests.fs b/src/LivingVillage.Desktop.Tests/MapGenTests.fs
index 4a09865..f426a8a 100644
--- a/src/LivingVillage.Desktop.Tests/MapGenTests.fs
+++ b/src/LivingVillage.Desktop.Tests/MapGenTests.fs
@@ -261,6 +261,37 @@ type MapGenTests () =
         Assert.AreEqual<int>(4, (MapGen.generateWithSize 64 48 (uint64 4242)).Buildings.Length)
         Assert.AreEqual<int>(4, (MapGen.generateWithSize 256 192 (uint64 4242)).Buildings.Length)
 
+    // ---- P25：大图不产孤立石板 tile（装饰石块默认开启仅限小图） ----
+
+    [<TestMethod>]
+    member _.DecorativeStonesDisabledOnLargeMaps () =
+        Assert.IsTrue((MapGen.paramsForSize 64 48 (uint64 1)).DecorativeStones)
+        Assert.IsTrue((MapGen.paramsForSize 256 192 (uint64 1)).DecorativeStones)
+        Assert.IsFalse((MapGen.paramsForSize 512 384 (uint64 1)).DecorativeStones)
+
+    [<TestMethod>]
+    member _.LargeMapHasNoIsolatedStoneTiles () =
+        let map = MapGen.generateWithSize 512 384 (uint64 4242)
+        let pathSet = System.Collections.Generic.HashSet<int>(map.Paths |> List.map (fun (x, y) -> y * map.Width + x))
+        let stone x y = map.Tiles.[y * map.Width + x] = int MapGen.GroundTile.Stone
+        let mutable isolated = 0
+        for y in 0 .. map.Height - 1 do
+            for x in 0 .. map.Width - 1 do
+                if stone x y && not (pathSet.Contains(y * map.Width + x)) then
+                    let neighbours =
+                        [ (x + 1, y); (x - 1, y); (x, y + 1); (x, y - 1) ]
+                        |> List.filter (fun (nx, ny) -> nx >= 0 && nx < map.Width && ny >= 0 && ny < map.Height)
+                        |> List.filter (fun (nx, ny) -> stone nx ny)
+                        |> List.length
+                    if neighbours = 0 then isolated <- isolated + 1
+        Assert.AreEqual<int>(0, isolated)
+        // 装饰关闭后，大图所有石板都应属于路网。
+        let stonesOutsidePaths =
+            [ for y in 0 .. map.Height - 1 do
+                  for x in 0 .. map.Width - 1 do
+                      if stone x y && not (pathSet.Contains(y * map.Width + x)) then yield (x, y) ]
+        Assert.AreEqual<int>(0, stonesOutsidePaths.Length)
+
     /// 锁定当前默认尺寸的生成结果，防止 P23 参数适配无意改变 64x48 / 256x192。
     [<TestMethod>]
     member _.DefaultSizeChecksumsArePinned () =