# Native road marking semantics

## Goal

Finish the native road marking model so the Nantaizi Road Workbench can
persist meaningful centre-line and road-edge-line styles, regenerate native
geometry deterministically, and deliver the same result to Blender/Cesium.

## Requirements

- Add an explicit double-yellow-solid centre-line semantic. It must not be a
  generic double-line switch that permits invalid colour/pattern combinations.
- Keep all marking edits area-local in `native-road-overrides.json`; generated
  GeoJSON remains derived output.
- Make road edge lines selectable and style-editable in the Chinese Road
  Workbench, alongside existing centre lines and lane separators.
- Preserve the default Nantaizi output unless a user supplies an override.
- Native geometry must remain independent of osm2streets render geometry.

## Acceptance Criteria

- [ ] A `center-line-style` override with `double: true`, `yellow`, and
  `solid` emits two offset centre-line polygons with an explicit effective
  style, while invalid double combinations are rejected.
- [ ] An `edge-line-style` override targets one directional road side and
  supports white/yellow plus solid/dashed styles.
- [ ] The Workbench exposes Chinese selection feedback, stages the correct
  override payload, and only shows the double-yellow choice for centre lines.
- [ ] Nantaizi native compile/check, Workbench/native tests, Blender pure
  tests, and native Blender/Cesium/preview build pass.

## Notes

- Keep `prd.md` focused on requirements, constraints, and acceptance criteria.
- Lightweight tasks can remain PRD-only.
- For complex tasks, add `design.md` for technical design and `implement.md` for execution planning before `task.py start`.