feat: add native road center lines

.trellis/tasks/08-13-native-road-compiler/task.json

@@ -20,7 +20,8 @@
   "subtasks": [],
   "children": [
     "08-14-native-road-lane-markings",
-    "08-17-native-road-control-markings"
+    "08-17-native-road-control-markings",
+    "08-17-native-road-center-lines"
   ],
   "parent": null,
   "relatedFiles": [],

.trellis/tasks/08-17-native-road-center-lines/check.jsonl

@@ -0,0 +1 @@
+{"_example": "Fill with {\"file\": \"<path>\", \"reason\": \"<why>\"}. Put spec/research files only — no code paths. Run `python3 .trellis/scripts/get_context.py --mode packages` to list available specs. Delete this line once real entries are added."}

.trellis/tasks/08-17-native-road-center-lines/design.md

@@ -0,0 +1,50 @@
+# Native Road Centre Lines Design
+
+## Architecture
+
+The native compiler adds one independent polygon layer:
+
+```text
+canonical bidirectional segment + trimmed OSM centreline
+  -> repeated 2m x 0.25m dash polygons
+  -> native-road/layers/center_lines.geojson
+  -> Workbench / native Blender adapter / Cesium
+```
+
+It does not read osm2streets `center_lines.geojson`. The legacy layer is a
+visual baseline only.
+
+## Placement
+
+- A candidate must have exactly forward and backward native roads for the same
+  `segmentId`, neither be `highway=service`, and have a valid trimmed OSM
+  centreline.
+- Dashes use the legacy observed dimensions: 2m length, 0.25m width, with a
+  deterministic 2m gap. The first dash starts at a fixed segment-local offset
+  so rebuilds do not drift.
+- The line is trimmed with the same `junctionPlans` cutback used by native lane
+  centreline generation. Any dash intersecting a crosswalk or stop line is
+  omitted, preserving the control-marking priority already established.
+- One-way and service segments have no generated feature. A degenerate source
+  line produces a diagnostic rather than malformed geometry.
+
+## Contracts
+
+`layers/center_lines.geojson` is a Polygon FeatureCollection. Every feature
+has `native_id`, `segment_id`, `directional_road_ids`, `osm_way_ids`,
+`dash_index`, `dash_length_m`, `dash_gap_m`, `placement_rule`, and
+`provenance="native-road-center-line/v1"`.
+
+`compiled.json.layers.centerLines`, comparison count
+`nativeCenterLineFeatures`, and `build-area.js` required native records use the
+same filename. `catalog.NATIVE_ROAD_LAYERS` maps source `center_lines` to the
+existing `center_lines` material layer.
+
+The Workbench loads this source into the marking overlay, exposes a Chinese
+toggle, and identifies it as `道路中心虚线` on selection.
+
+## Compatibility
+
+The change is additive within `native-road/`; `--road-provider osm2streets`
+remains unaffected and is rollback. A native Blender build treats a missing
+layer as an input error rather than silently omitting it.

.trellis/tasks/08-17-native-road-center-lines/implement.jsonl

@@ -0,0 +1 @@
+{"_example": "Fill with {\"file\": \"<path>\", \"reason\": \"<why>\"}. Put spec/research files only — no code paths. Run `python3 .trellis/scripts/get_context.py --mode packages` to list available specs. Delete this line once real entries are added."}

.trellis/tasks/08-17-native-road-center-lines/implement.md

@@ -0,0 +1,19 @@
+# Implementation Plan
+
+1. Add centre-dash constants and a pure native compiler routine based on the
+   shared bidirectional segment model and junction-trimmed centreline.
+2. Filter invalid, one-way, service, and control-marking-conflicting dashes;
+   record actionable diagnostics for invalid geometry only.
+3. Write `center_lines.geojson`, compilation/comparison counts, native build
+   records, required-layer checks, and Blender material adapter mapping.
+4. Add Workbench API state, Chinese toggle, summary count, rendering, and
+   source evidence for a selected centre dash.
+5. Add focused native and Workbench tests for generation, skips, control
+   avoidance, provenance, and file/API contracts.
+6. Run native/unit/workbench/build-stage tests, compile/check Nantaizi, then
+   validate `blender,cesium,preview --road-provider native` without `package`.
+
+## Rollback
+
+Choose `--road-provider osm2streets`; no legacy layer or published package is
+modified.

.trellis/tasks/08-17-native-road-center-lines/prd.md

@@ -0,0 +1,58 @@
+# Native road center lines
+
+## Goal
+
+Restore the existing osm2streets-style road-centre dashed markings in the
+native-road provider before treating native output as ready for broader quality
+gates or new-area validation.
+
+## Confirmed Facts
+
+- Nantaizi's existing `osm2streets_web_out/center_lines.geojson` has 885
+  `type="center line"` polygons. Its sampled dash geometry is approximately
+  2.00m long by 0.25m wide.
+- The legacy extraction excludes centre lines that overlap crosswalk zones and
+  that fall on service driving polygons (`build-osm2streets-qgis.js:474-480`).
+- Native output currently has only same-direction `lane_separators`; it has no
+  `center_lines.geojson`, so a bidirectional road's directional carriageways
+  lack their visual and semantic divider.
+- Existing Blender already owns a `center_lines` / `Center Line` material
+  layer. Native must adapt to it rather than creating a second scene registry.
+
+## Requirements
+
+- R1: For supported non-service, bidirectional native road segments, emit a
+  `center_lines.geojson` dashed centre divider derived from the canonical OSM
+  centreline and the segment's two directional carriageways.
+- R2: Match the established visual baseline: yellow 0.25m-wide, 2m-long
+  dashes, clipped away from ordinary junction cutbacks and control markings.
+- R3: Preserve source traceability: each dash records its native segment,
+  source OSM way, involved directional roads, placement interval/rule, and a
+  dedicated provenance value.
+- R4: Add the layer to compilation records, Road Workbench display/selection
+  in Chinese, and the existing Blender/Cesium `center_lines` material path.
+- R5: Do not render a centre divider on one-way or `highway=service` segments;
+  report invalid geometry instead of fabricating a divider.
+
+## Acceptance Criteria
+
+- [ ] Native Nantaizi output contains a valid `layers/center_lines.geojson`
+  with source-traceable 2m x 0.25m dashed polygons.
+- [ ] No native centre dash intersects a generated crosswalk or vehicle stop
+  line, and no dash reaches into the supported junction surface cutback.
+- [ ] The Workbench can toggle and select centre lines, presenting their
+  source and rule in Chinese rather than calling them lane separators.
+- [ ] Native `blender,cesium,preview` consumes the layer using the existing
+  `center_lines` material and does not run `package`.
+- [ ] Tests cover two-way generation, one-way/service skips, control-marking
+  avoidance, provenance, output contract, and Workbench wiring.
+
+## Out Of Scope
+
+- Centre-line editing overrides, solid/double-centre-line semantics, arbitrary
+  OSM `overtaking` interpretation, lane colouring changes, and other areas.
+
+## Key Decision
+
+This task deliberately matches the existing stable visual layer first. It does
+not claim to infer a country-wide legal marking taxonomy from sparse OSM tags.

.trellis/tasks/08-17-native-road-center-lines/task.json

@@ -0,0 +1,26 @@
+{
+  "id": "native-road-center-lines",
+  "name": "native-road-center-lines",
+  "title": "Native road center lines",
+  "description": "Align native-road output with the existing center_lines layer before broader quality work.",
+  "status": "in_progress",
+  "dev_type": null,
+  "scope": null,
+  "package": null,
+  "priority": "P2",
+  "creator": "dingkang",
+  "assignee": "dingkang",
+  "createdAt": "2026-08-17",
+  "completedAt": null,
+  "branch": null,
+  "base_branch": "feature/native-road-compiler",
+  "worktree_path": null,
+  "commit": null,
+  "pr_url": null,
+  "subtasks": [],
+  "children": [],
+  "parent": "08-13-native-road-compiler",
+  "relatedFiles": [],
+  "notes": "",
+  "meta": {}
+}