# Native road control markings

## Goal

Give Nantaizi's native-road provider inspectable, source-traceable crosswalk
and vehicle stop-line geometry, so intersection control markings do not depend
on the osm2streets render output.

## Confirmed Facts

- Native road output already owns road surfaces, sidewalks, lane separators,
  repeated direction arrows, and explicit junction-turn arrows.
- Nantaizi's OSM input contains explicit marked crossings, including zebra and
  traffic-signal crossings. The existing osm2streets output currently has 48
  crosswalk-stripe polygons and 8 stop-line polygons.
- `build-osm2streets-qgis.js:1067` derives these markings from crossing nodes
  plus osm2streets driving lanes. Native must not read that rendered geometry;
  it can reuse only the tested geometry rules after adapting them to native
  directed lanes and junction plans.
- Existing Blender materials already provide `crosswalks` and
  `vehicle_stop_lines`; native may map into them without changing the legacy
  osm2streets layer registry.

## Requirements

- R1: Native compilation uses explicit marked OSM crossing nodes only, and
  emits crosswalk-stripe polygons plus approach stop lines only where safe
  native directed-road placement exists.
- R2: Each generated feature preserves crossing node, OSM road, native road or
  lane, direction, placement method, and relevant junction provenance.
- R3: The Road Workbench independently toggles, selects, and describes native
  crosswalks and stop lines in Chinese.
- R4: Native Blender and Cesium builds consume both layers with the existing
  control-marking materials; no `package/` publication is part of validation.
- R5: Missing compatible road context, ambiguous geometry, and unsupported
  crossing inputs are diagnostics; the compiler must not invent a crossing.

## Acceptance Criteria

- [ ] Nantaizi native output contains valid `crosswalks.geojson` and
  `vehicle_stop_lines.geojson` features with source-traceable properties,
  without reading osm2streets rendered layers.
- [ ] A Workbench user can toggle and select either marking type and see the
  crossing node, associated road/direction, and placement evidence.
- [ ] Native Blender/Cesium output contains both marking types using existing
  materials, after `blender,cesium,preview --road-provider native` and without
  publishing `package/`.
- [ ] Tests cover a marked crossing, an unmarked crossing skip, a missing or
  ambiguous native-road placement skip, and output-layer contract checks.

## Out Of Scope

- Hand-placed control-marking overrides, traffic-signal state-machine changes,
  freehand polygon editing, processing another region, and importing
  osm2streets-rendered crosswalk geometry.

## Key Decision

The first version is explicit-OSM-only. This is feasible for Nantaizi and
keeps control markings evidence-backed; missing data remains a diagnostic for
OSM improvement rather than a silent geometric guess.