# Native road center line style overrides

## Goal

Allow a Road Workbench user to select a generated native road centre line and
persistently override its marking style, without turning the generated GeoJSON
into the source of truth.

## Confirmed Facts

- Native `center_lines.geojson` currently contains automatic yellow dashed
  polygons (`2m` dash, `2m` gap, `0.25m` width), each tied to a `segment_id`.
- A displayed dash can already be selected and exposes its segment provenance,
  but has no editing controls.
- `native-road-overrides.json` is the persistent authority for existing road
  and connection edits. The Workbench already stages, validates, saves, then
  recompiles those overrides.
- The generated layer is consumed by both Workbench and native Blender/Cesium;
  styling must therefore be compiled geometry and use the existing
  `center_lines` material path, not a Workbench-only display tint.

## Requirements

- R1: Selecting a centre-line dash must expose a Chinese style editor for its
  logical target and show the current effective style.
- R2: Supported styles must include at least solid/dashed and white/yellow
  marking colours.
- R3: Style choices must be stored in `native-road-overrides.json`, validated,
  reapplied during compilation, and survive a future Workbench launch.
- R4: The regenerated GeoJSON must carry source traceability and effective
  style fields so Workbench, Blender and Cesium show the same marking.
- R5: Default automatic centre lines remain unchanged for segments without an
  override; one-way/service exclusions and control-marking avoidance remain
  authoritative.

## Initial Scope Boundary

- Editing individual dash polygons is out of scope: they are derived pieces,
  not user-owned objects.
- Per-segment control is recommended for the first version because current
  native segments already stop at junctions and have stable IDs.
- Double-line semantics, legal `overtaking` inference, hand-drawn partial
  ranges, and changes to osm2streets output are out of scope unless explicitly
  accepted during planning.

## Acceptance Criteria

- [ ] A user can select a centre line, choose a supported style in Chinese,
  save it, regenerate, and see the result immediately in the Workbench.
- [ ] After reload and recompilation, the selected segment retains its style
  while unedited segments retain the automatic yellow dashed default.
- [ ] Native Blender/Cesium uses the same effective style and does not require
  osm2streets geometry.
- [ ] Tests cover schema validation, style geometry, default fallback,
  persistence/API wiring, and Workbench selection/edit controls.

## Key Decisions

- The first version applies one override to the complete native segment between
  junctions. Individual dash and partial-range editing are deferred.
- The initial style catalog is four explicit choices: yellow dashed, white
  dashed, yellow solid, and white solid. Double-line semantics are deferred.