feat: osm2streets上游箭头修复

README.md

@@ -78,6 +78,9 @@ cp config/examples/template.json config/areas/my-area.json
   },
   "qgis": {
     "arrowScale": 0.8,
+    "arrowMergeTriangles": true,
+    "arrowOutlineSimplifyMeters": 0.05,
+    "intersectionCornerSourceMaxDimensionMeters": 2.6,
     "clipPad": 0.002,
     "canvasPad": 0.001,
     "previewPad": 0.0007,
@@ -92,6 +95,13 @@ cp config/examples/template.json config/areas/my-area.json
 }
 ```
 
+QGIS road-layer knobs:
+
+- `arrowScale`: scales osm2streets lane-arrow polygons before export.
+- `arrowMergeTriangles`: merges each osm2streets lane-arrow triangle mesh into one valid polygon. This preserves the original arrow shape and turn direction while removing renderer gaps along shared triangle edges.
+- `arrowOutlineSimplifyMeters`: removes sub-decimeter kinks from the merged arrow exterior. The default `0.05` removes the two malformed tail vertices without changing the arrow head; the remaining tail edge is aligned perpendicular to the shaft.
+- `intersectionCornerSourceMaxDimensionMeters`: keeps only small osm2streets `sidewalk corner` polygons. Large intersection-marking polygons are not treated as sidewalk because they can cover the drivable junction.
+
 `scripts/build-area.js` 会按 `id` 自动推导默认输出路径。确实需要定制时，可以增加 `outputs` 覆盖：
 
 ```json