标记便签在地平线附近渐变淡出，修复拖拽闪烁

src/scene/CesiumGlobe.js

@@ -321,12 +321,19 @@ export class CesiumGlobe {
       const win = Cesium.SceneTransforms.worldToWindowCoordinates(scene, m.position);
       if (!win) { el.style.display = 'none'; continue; }
 
-      // 背面（远半球）隐藏：dot(P, C) <= |P|² 时为背对地球
+      // 前/后半球判断 + 地平线附近渐变淡出（固定 ~3° 渐变带，避免拖拽时闪烁/突隐）
       const dotPC = Cesium.Cartesian3.dot(m.position, camera.positionWC);
-      const r2 = Cesium.Cartesian3.magnitudeSquared(m.position);
-      if (dotPC <= r2) { el.style.display = 'none'; continue; }
+      const pMag = Math.sqrt(Cesium.Cartesian3.magnitudeSquared(m.position));
+      const cMag = Cesium.Cartesian3.magnitude(camera.positionWC);
+      const cosPhi = dotPC / (pMag * cMag);
+      const phi = Math.acos(Math.max(-1, Math.min(1, cosPhi)));
+      const phiHorizon = Math.acos(Math.max(-1, Math.min(1, pMag / cMag)));
+      const margin = phiHorizon - phi; // > 0 为前半球
+      if (margin <= 0) { el.style.display = 'none'; continue; }
+      const opacity = Math.min(1, margin / 0.05); // 0.05 rad ≈ 3°
 
       el.style.display = 'block';
+      el.style.opacity = String(opacity);
       el.style.left = `${win.x}px`;
       el.style.top = `${win.y}px`;
     }