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diff --git a/src/LivingVillage.Desktop.Tests/P40ArtTests.fs b/src/LivingVillage.Desktop.Tests/P40ArtTests.fs
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+namespace LivingVillage.Desktop.Tests
+
+open Microsoft.VisualStudio.TestTools.UnitTesting
+open LivingVillage.Kernel.Sim
+open LivingVillage.Desktop
+open LivingVillage.Desktop.VillageArt
+
+/// P40 art-deepening slice:
+///  * paving slabs follow the traffic network (paths / doorways / bridges) and the
+///    isolated decorative scatter is dropped, so cc0 ground reads as coherent bands;
+///  * red door lanterns complement the stone road lanterns with a distinct form,
+///    both feeding the existing P14 premultiplied-alpha night-glow path;
+///  * every placement stays a pure function of the map, so the same seed yields
+///    byte-identical positions across day and night frames.
+[<TestClass>]
+type P40ArtTests () =
+
+    let seed = 4242UL
+    let map = MapGen.generateWithSize 256 192 seed
+
+    let indexOf (x: int) (y: int) = y * map.Width + x
+    let isStone (x: int) (y: int) =
+        x >= 0 && x < map.Width && y >= 0 && y < map.Height
+        && map.Tiles.[indexOf x y] = int MapGen.GroundTile.Stone
+
+    [<TestMethod>]
+    member _.PavingCoversTrafficNetworkAndDropsIsolatedScatter () =
+        let paving = cc0PavingTiles map
+        Assert.IsTrue(paving.Count > 0, "seed 4242 should pave something")
+        // Every path / bridge anchor tile that is stone must be paved.
+        for (x, y) in map.Paths @ map.Bridges do
+            if isStone x y then
+                Assert.IsTrue(paving.Contains(indexOf x y), sprintf "path/bridge stone (%d,%d) must be paved" x y)
+        // Every paved tile must be stone and touch the network (itself or a 4-neighbour).
+        let anchors = (map.Paths @ map.Bridges) |> List.map (fun (x, y) -> indexOf x y) |> Set.ofList
+        let anchorAt (x: int) (y: int) =
+            x >= 0 && x < map.Width && y >= 0 && y < map.Height && Set.contains (indexOf x y) anchors
+        for i in paving do
+            let x = i % map.Width
+            let y = i / map.Width
+            Assert.IsTrue(isStone x y, "paving must only replace stone tiles")
+            Assert.IsTrue(
+                anchorAt x y || anchorAt (x - 1) y || anchorAt (x + 1) y || anchorAt x (y - 1) || anchorAt x (y + 1),
+                sprintf "paved tile (%d,%d) is disconnected from the traffic network" x y)
+        // The isolated decorative scatter must NOT be paved (that is the whole point).
+        Assert.IsTrue(paving.Count < (map.Tiles |> Array.filter (fun c -> c = int MapGen.GroundTile.Stone) |> Array.length),
+                      "paving must be a strict subset of all stone (scatter dropped)")
+
+    [<TestMethod>]
+    member _.PavingIsDeterministicForTheSameSeed () =
+        let map2 = MapGen.generateWithSize 256 192 seed
+        let a = cc0PavingTiles map |> Set.toList |> List.sort |> List.map (fun i -> sprintf "%d" i) |> String.concat ";"
+        let b = cc0PavingTiles map2 |> Set.toList |> List.sort |> List.map (fun i -> sprintf "%d" i) |> String.concat ";"
+        Assert.AreEqual<string>(a, b)
+
+    [<TestMethod>]
+    member _.RedLanternsHangAtDoorwaysAndAreDeterministic () =
+        let lanterns = cc0RedLanternTiles map
+        let doors =
+            (map.Buildings @ map.Farmhouses)
+            |> List.map (fun b -> (b.DoorX, b.DoorY))
+            |> List.distinct
+        Assert.IsTrue(lanterns.Length > 0, "seed 4242 should hang red lanterns")
+        Assert.AreEqual<int>(doors.Length, lanterns.Length)
+        for (x, y) in lanterns do
+            Assert.IsTrue(List.contains (x, y) doors, "a red lantern hangs exactly at a doorway")
+        Assert.AreEqual<string>(
+            (lanterns |> List.sort |> List.map (fun (x, y) -> sprintf "%d:%d" x y) |> String.concat ";"),
+            (cc0RedLanternTiles map |> List.sort |> List.map (fun (x, y) -> sprintf "%d:%d" x y) |> String.concat ";"))
+
+    [<TestMethod>]
+    member _.RedAndStoneLanternsFeedTheSameNightGlowPath () =
+        let cc0Lights = nightLightTilesWith true map |> Set.ofList
+        let fallbackLights = nightLightTilesWith false map |> Set.ofList
+        // cc0 mode adds both the road stone lanterns and the red door lanterns.
+        for t in cc0RedLanternTiles map do
+            Assert.IsTrue(Set.contains t cc0Lights, "red lantern must be a cc0 night light")
+        for t in cc0LanternTiles map 12 do
+            Assert.IsTrue(Set.contains t cc0Lights, "road lantern must be a cc0 night light")
+        // Red lanterns hang at doorways, which are already house lights, so the
+        // fallback set may legitimately contain that tile; what must NOT leak is
+        // the road stone lantern set (a cc0-only placement).
+        for t in cc0LanternTiles map 12 do
+            Assert.IsFalse(Set.contains t fallbackLights, "road lantern must not leak into the fallback light set")
+        Assert.IsTrue(nightLightTiles map = nightLightTilesWith false map, "nightLightTiles keeps the old set")
+        Assert.IsTrue(Set.isSubset fallbackLights cc0Lights, "cc0 light set is a superset of the fallback set")
+
+    [<TestMethod>]
+    member _.SameSeedPlacementsAreStableAcrossGeneration () =
+        // Day and night frames reuse the same map; re-generating it must reproduce
+        // every P40 placement byte-for-byte (no clock, no hidden randomness).
+        let map2 = MapGen.generateWithSize 256 192 seed
+        Assert.AreEqual<string>(
+            (cc0PavingTiles map |> Set.toList |> List.sort |> List.map string |> String.concat ";"),
+            (cc0PavingTiles map2 |> Set.toList |> List.sort |> List.map string |> String.concat ";"))
+        Assert.AreEqual<string>(
+            (cc0RedLanternTiles map |> List.sort |> List.map (fun (x, y) -> sprintf "%d:%d" x y) |> String.concat ";"),
+            (cc0RedLanternTiles map2 |> List.sort |> List.map (fun (x, y) -> sprintf "%d:%d" x y) |> String.concat ";"))
+
+    [<TestMethod>]
+    member _.P40AtlasIndicesAreInRange () =
+        for index in [ cc0TileIndexPaving; cc0TileIndexRedLantern ] do
+            Assert.IsTrue(index >= 0 && index < cc0TileCount, sprintf "P40 tile index %d out of atlas" index)
+        Assert.AreEqual<int>(21, cc0TileCount)