chore(task): archive 08-17-native-road-center-line-styles

.trellis/tasks/archive/2026-08/08-17-native-road-center-line-styles/prd.md

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+# 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.