p79: 夜帧炊烟增强与光晕去叠

- 炊烟：夜帧烟柱4段向上堆叠(整格32px, alpha 180+75)+暖色外发光(r30)+中性柔光团(r12)；
  烟柱强光像素(夜-昼贡献>=80) 181->1171 (x6.5)，峰值112->173；白天帧逐像素不变。
- 光晕去叠：VillageArt.haloRingLayers 每光源<=2层(内芯+空心外环)，芯环间确定暗隙，半径4->3 tile，
  峰值150->118；光晕重叠面积(夜-昼贡献>=60)中央区 15184->9633 (-36.6%)，全屏 15477->9926 (-35.9%)。
- 回归 P79NightPolishTests(3)；analyze-p78.py 复跑仍 PASS；正午帧与 P78 完全一致=白天零回归。
- Desktop 367/367, Kernel 120/120, digest 953775FA...F7F6C 不变

1 files changed, 46 insertions, 0 deletions

diff --git a/src/LivingVillage.Desktop/VillageArt.fs b/src/LivingVillage.Desktop/VillageArt.fs
index db594d2..c797270 100644
--- a/src/LivingVillage.Desktop/VillageArt.fs
+++ b/src/LivingVillage.Desktop/VillageArt.fs
@@ -538,6 +538,52 @@ module VillageArt =
                       for (x, y, width) in ellipseRuns centerX centerY ringRadius ringRadius do
                           yield (Microsoft.Xna.Framework.Rectangle(x, y, width, 1), glowColor) ]
 
+    /// P79：单光源夜景光晕（去叠版）——最多 2 层视觉层：内芯（2 圈递减填充）+ 外环（空心圆环）。
+    /// 芯与环之间留一圈确定暗隙（不被任何 rect 覆盖），于是相邻多光源不会叠成一整团；
+    /// 累计 alpha 仍以 peakAlpha 为峰，不因层数而加深。半径由调用方收紧。
+    let haloRingLayers
+        (centerX: int)
+        (centerY: int)
+        (radius: int)
+        (peakAlpha: int) : (Microsoft.Xna.Framework.Rectangle * Microsoft.Xna.Framework.Color) list =
+        if radius <= 3 || peakAlpha <= 0 then
+            []
+        else
+            let innerRadius = max 1 (radius * 2 / 5)
+            let gapRadius = max (innerRadius + 2) (radius * 3 / 5)
+            let outerRadius = radius
+            // 内芯：两圈递减填充，累计峰值 = peakAlpha，不再加深。
+            let coreTarget (ringRadius: int) =
+                int (Math.Round(float peakAlpha * float (lanternFalloff (float32 ringRadius) (float32 innerRadius)), MidpointRounding.AwayFromZero))
+            let mutable previous = 0
+            let innerLayers =
+                [ for ringRadius in [ innerRadius; max 1 (innerRadius / 2) ] do
+                      let target = coreTarget ringRadius
+                      let increment = max 0 (target - previous)
+                      previous <- max previous target
+                      if increment > 0 then
+                          for (x, y, width) in ellipseRuns centerX centerY ringRadius ringRadius do
+                              yield (Microsoft.Xna.Framework.Rectangle(x, y, width, 1), premultiply 255 214 150 increment) ]
+            // 外环：空心圆环（外半径 outerRadius、内孔 gapRadius），只画左右两段，与内芯之间留暗隙。
+            let ringColor = premultiply 255 214 150 (max 1 (peakAlpha / 2))
+            let ringLayers =
+                [ for y in centerY - outerRadius .. centerY + outerRadius do
+                      let dy = y - centerY
+                      let halfAt (r: int) =
+                          let squared = r * r - dy * dy
+                          if squared <= 0 then 0 else int (sqrt (float squared))
+                      let outerHalf = halfAt outerRadius
+                      let gapHalf = halfAt gapRadius
+                      if outerHalf > 0 then
+                          if gapHalf <= 0 then
+                              yield (Microsoft.Xna.Framework.Rectangle(centerX - outerHalf, y, outerHalf * 2 + 1, 1), ringColor)
+                          else
+                              let leftWidth = outerHalf - gapHalf
+                              if leftWidth > 0 then
+                                  yield (Microsoft.Xna.Framework.Rectangle(centerX - outerHalf, y, leftWidth, 1), ringColor)
+                                  yield (Microsoft.Xna.Framework.Rectangle(centerX + gapHalf + 1, y, outerHalf - gapHalf, 1), ringColor) ]
+            innerLayers @ ringLayers
+
     /// Characters spawn at tile centres; push the sprite down half a tile so its feet rest
     /// on the tile's ground line instead of floating at the centre.
     let characterFeetOffset = Sim.tilePixels / 2