feat: add native road marking semantics

.trellis/tasks/08-17-native-road-marking-semantics/check.jsonl

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+{"file":".trellis/spec/pipeline/cli-and-stages.md","reason":"Check compiler and workbench marking contracts."}
+{"file":".trellis/spec/blender/testing.md","reason":"Run required Blender test suite."}
+{"file":".trellis/spec/guides/cross-layer-thinking-guide.md","reason":"Verify browser, compiler, and Blender consume the same output."}

.trellis/tasks/08-17-native-road-marking-semantics/design.md

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+# Design
+
+The compiler owns marking semantics. `center-line-style` remains segment
+scoped because a bidirectional road segment shares one centre-line decision.
+`edge-line-style` is scoped to `{ roadId, side }`, since a directional
+carriageway has independently editable left and right outside edges.
+
+`double: true` is valid only with yellow solid centre lines. Generation emits
+two 0.32m-separated parallel polygons for each normal solid mark, preserving
+junction cutback and crosswalk/stop-line clearance. This keeps the existing
+solid line implementation and avoids a separate geometry pipeline.
+
+Road edge lines use the existing road-edge offset geometry. A solid style is
+one continuous buffered offset line; a dashed style uses deterministic 2m
+marks at 4m spacing. Both carry `effective_style`, source IDs, side, and
+native provenance.
+
+The Workbench uses one marking form with an explicit selected target type.
+Only a centre-line target exposes the double-yellow option; lane separators
+and edge lines retain the ordinary colour/pattern choices. Staged changes pass
+through the existing save and regenerate flow, so browser, compiler and
+Blender read the same persisted override.

.trellis/tasks/08-17-native-road-marking-semantics/implement.jsonl

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+{"file":".trellis/spec/pipeline/cli-and-stages.md","reason":"Native-road output, override, and stage contracts."}
+{"file":".trellis/spec/blender/asset-generation.md","reason":"Native provider adapter and Blender output requirements."}
+{"file":".trellis/spec/guides/artifact-parity-guide.md","reason":"Intentional render-output change validation."}

.trellis/tasks/08-17-native-road-marking-semantics/implement.md

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+# Implementation
+
+1. Extend override validation and native marking generation for explicit
+   double-yellow centre lines and per-side edge-line styles.
+2. Extend the Chinese Workbench selection/form flow without adding another
+   editor or output format.
+3. Add compiler and Workbench regression coverage for valid and invalid
+   payloads, generated geometry, and layer adapter completeness.
+4. Compile/check Nantaizi, run native/Workbench/build-stage/Blender tests,
+   then run the native Blender/Cesium/preview chain.

.trellis/tasks/08-17-native-road-marking-semantics/prd.md

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+# 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`.

.trellis/tasks/08-17-native-road-marking-semantics/task.json

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+{
+  "id": "native-road-marking-semantics",
+  "name": "native-road-marking-semantics",
+  "title": "Native road marking semantics",
+  "description": "",
+  "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": null,
+  "relatedFiles": [],
+  "notes": "",
+  "meta": {}
+}