feat: add OSM turn lane arrows

.trellis/tasks/08-04-add-osm-turn-lane-arrows/check.jsonl

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+{"file":".trellis/spec/pipeline/index.md","reason":"Defines the expected intermediates artifacts and dependency boundaries."}
+{"file":".trellis/spec/pipeline/layer-registry.md","reason":"Requires preserving existing lane-arrow layer collection and order across QGIS and Blender."}
+{"file":".trellis/spec/pipeline/cli-and-stages.md","reason":"Defines quality-gate and target-area validation expectations."}
+{"file":".trellis/tasks/08-04-add-osm-turn-lane-arrows/research/lane-icons.md","reason":"Defines the source provenance and assertion that untested assets cannot be mapped."}

.trellis/tasks/08-04-add-osm-turn-lane-arrows/design.md

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+# Design: OSM turn-lane arrows
+
+## Boundaries
+
+- `scripts/build-osm2streets-qgis.js` remains the intermediates owner. It will
+  append generated custom features to the existing in-memory `laneArrows`
+  collection before it is written as `lane_arrows_webscale.geojson`.
+- No render layer, QGIS symbol, Blender material, or Cesium export contract
+  changes. Existing `lane_arrows_webscale` styling and catalog ownership apply
+  to generated features automatically.
+- Vendored upstream artwork lives under a dedicated repository-local asset
+  directory with its CC0 license and a machine-readable manifest. The manifest
+  is the source of truth for upstream path, source revision, local path,
+  support status, and test status.
+
+## Asset Contract
+
+- Import every arrow SVG from `openstreetmap/lane-icons/docs/` that represents
+  an arrow. Preserve the source bytes and retain `LICENSE.md` with the assets.
+- Mark only `through`, `left`, `right`, `through;left`, and `through;right` as
+  `supported` and `tested` in the manifest. All remaining imported arrows are
+  `unsupported` and `untested`; no production parser may select them.
+- The upstream repository has left-side examples only. Derive `right` and
+  `through;right` through a deterministic horizontal mirror of the matching
+  left-side geometry, recording `derived_from` in the manifest.
+
+## Data Flow
+
+1. Parse OSM ways once using the existing OSM parser.
+2. Read `turn:lanes:forward` / `turn:lanes:backward`, split lane declarations
+   by `|`, and map only the five supported normalized maneuvers to manifest
+   entries.
+3. For each valid lane near a determinable intersection endpoint, calculate a
+   stable lane center and road-local axis; transform the selected local arrow
+   polygon into WGS84 coordinates.
+4. Add a GeoJSON feature with existing render-layer behavior and explicit
+   provenance: custom source, OSM way id, direction, lane index, maneuver,
+   source asset, and deterministic feature id/order.
+5. Record a structured skipped item when tags, lane geometry, or endpoint
+   classification are insufficient. Do not invent a fallback location.
+6. Existing normalization, scene merge, GeoPackage import, Blender assembly,
+   and Cesium export consume the expanded collection unchanged.
+
+## Geometry and Compatibility
+
+- Parse only the vendored SVG subset used by supported assets at build time:
+  `line` elements and `path` commands are converted into local meter-scale
+  polygons, with cubic curves sampled and SVG strokes expanded into outlines.
+  The source SVG is the sole geometry authority; no hand-drawn replacement
+  template is permitted. This stays dependency-free because the supported
+  upstream syntax is intentionally small and covered by Node tests.
+- Use the upstream Standard Arrow shape as the geometry basis, but let the
+  existing QGIS fill and outline preserve the project's visual language.
+- Preserve the existing osm2streets-generated arrow features. Custom features
+  are additive and have provenance that distinguishes them from upstream
+  osm2streets output.
+- Deterministic ordering is by way id, travel direction, and lane index.
+- Each asset manifest entry defines the source SVG's shaft-axis `anchor_x`.
+  Placement aligns that axis, rather than the SVG viewBox center, with the
+  lane centerline. Mirrored right-side variants mirror around the same axis.
+- Upstream SVG units are converted at `0.10 m` per unit. This calibrates their
+  local extent against the existing approximately 1.4 m osm2streets arrows;
+  do not use SVG display-pixel scale as road-marking scale.
+
+## Risks and Rollback
+
+- OSM lane counts, one-way semantics, or endpoint topology can be incomplete.
+  These cases remain skipped with diagnostics rather than creating misleading
+  markings.
+- Asset import is self-contained and CC0. Rollback removes the custom feature
+  generation and local asset directory; the existing arrow layer remains
+  unchanged.
+- User approval of the two initial visual samples is required before the
+  feature is enabled in production output.

.trellis/tasks/08-04-add-osm-turn-lane-arrows/implement.jsonl

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+{"file":".trellis/spec/pipeline/index.md","reason":"Defines the intermediates data flow, CommonJS conventions, and existing layer ownership."}
+{"file":".trellis/spec/pipeline/layer-registry.md","reason":"The feature adds a source to an existing layer and must preserve the cross-language layer contract."}
+{"file":".trellis/spec/pipeline/cli-and-stages.md","reason":"Defines stage ownership and target-area validation commands."}
+{"file":".trellis/tasks/08-04-add-osm-turn-lane-arrows/research/lane-icons.md","reason":"Records the selected upstream SVG source, CC0 provenance, and supported-versus-untested asset policy."}

.trellis/tasks/08-04-add-osm-turn-lane-arrows/implement.md

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+# Implementation Plan: OSM turn-lane arrows
+
+## Steps
+
+1. Add the complete lane-icons arrow asset set, upstream revision metadata,
+   CC0 license text, and a manifest with the five supported/tested entries and
+   explicit untested status for all other entries.
+2. Add a small CommonJS helper for asset-manifest loading, source-SVG path and
+   stroke conversion, maneuver parsing, road-local placement, and diagnostic
+   skip records. Keep it dependency-free and separately testable.
+3. Wire the helper into the intermediates build so custom features are merged
+   into `laneArrows` before the existing GeoJSON write and normalization path.
+4. Add Node tests for the five supported maneuvers, forward/backward endpoint
+   choice, lane index placement, deterministic order/id, and every required
+   skip reason. Assert that untested manifest entries cannot be selected.
+5. Generate `right` and `through;right` inspection samples from the exact
+   local templates and request user confirmation. Do not enable custom output
+   until this gate is met.
+6. Run the focused tests, syntax checks, the Nantaizi intermediates build, the
+   full Nantaizi chain, and `check:area`. Compare against a turn-tag-removed
+   control to prove an observable GeoJSON difference.
+
+## Validation
+
+- `node --check` for changed CommonJS scripts.
+- New pure Node test script(s), invoked directly or through a package script.
+- `npm run build:area -- --config config/areas/nantaizi-lake-innovation-valley.json --stages intermediates`
+- Full target-area pipeline after visual approval.
+- `npm run check:area -- --config config/areas/nantaizi-lake-innovation-valley.json`
+
+## Review Gates
+
+- No generated custom feature may use an asset whose manifest status is not
+  both supported and tested.
+- Samples must show the same fill/outline treatment as the existing lane-arrow
+  layer.
+- Keep the existing layer registry unchanged; this is a new source for an
+  existing layer, not a new layer.
+- Do not commit without the user's explicit confirmation.

.trellis/tasks/08-04-add-osm-turn-lane-arrows/prd.md

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+# Add OSM turn lane arrows
+
+## Goal
+
+让 OSM `turn:lanes:forward` / `turn:lanes:backward` 在现有 QGIS -> Blender -> Cesium
+道路链中生成可辨识的 lane arrow，同时保持与 osm2streets 既有道路标线相同的视觉语言。
+
+## Confirmed Facts
+
+- 当前 `osm2streets-js-node@0.1.4` 生成 lane arrow，但纯内存移除 way `98607123`、
+  `98607128`、`98607147` 的 `turn:lanes:*` 后，593 个原始箭头的 JSON 内容逐字一致；
+  因此该依赖不消费这些 OSM 标签。
+- 当前南台子完整链已经通过：中间层落盘 580 个归一化箭头，Blender 装配 397 个，
+  Cesium / preview / compress manifest 均 fresh，`check:area` PASS。
+- 现有 `lane_arrows_webscale` 已是 QGIS、Blender、Cesium 共用图层，样式为浅色填充
+  `#fffff6`、深色描边 `#2b2b28`，正常外轮廓为七顶点箭头。
+- `turn:lanes:forward=right`、`turn:lanes:backward=through;right` 等标准标签已存在于
+  南台子 OSM。
+- `openstreetmap/lane-icons` 是 OSM 官方组织发布的 CC0 SVG 图标集；其 `DESIGN.md`
+  以 MUTCD Standard Arrow 为基准，并规定组合转向共享箭杆、箭头数量增加时缩小箭头。
+  仓库只提供左侧转向示例，右转及 `through;right` 需在几何层对其镜像，不能直接作为
+  当前 GeoJSON polygon 图层输入。
+- 用户已决定将该库中首版需要的转向图标作为本仓库维护的源素材，而不是只作为视觉参考。
+
+## Requirements
+
+1. 在写入 `lane_arrows_webscale.geojson` 前，从 OSM 标准 `turn:lanes:*` 生成自定义箭头
+   polygon，并沿用既有图层、材质、QGIS/Blender/Cesium 路径。
+2. 支持首版实际需要的 `through`、`left`、`right`、`through;left`、`through;right`；
+   同一 OSM 输入必须产生确定性结果。
+3. 自定义箭头必须使用现有道路标线的视觉语言，不新建一套颜色、描边或图标风格。
+4. 在 OSM way 进入路口的一端、按 forward/backward 和 lane index 放置；车道配置不完整或
+   端点不是可判定路口时给出可诊断的跳过原因。
+5. 首先完成并获得用户对 `right` 和 `through;right` 轮廓样张的确认，之后才能将其接入
+   GeoJSON / Blender 导出。
+6. 未经用户确认，不提交 Git。
+7. 将 `openstreetmap/lane-icons` 的全部箭头 SVG 和 CC0 许可证说明纳入本仓库维护；
+   右转变体由左转源图镜像生成。生成的 polygon 仍由本仓库维护，并继续使用
+   `lane_arrows_webscale` 的既有填充与描边样式。
+8. 素材清单必须逐项标记验证状态：仅 `through`、`left`、`right`、`through;left`、
+   `through;right` 在首版具备 OSM 映射与自动化测试；其他已收录箭头明确标为未测试，
+   且不得自动参与生产 GeoJSON 输出。
+
+## Acceptance Criteria
+
+- [ ] 用户确认箭头样张的轮廓与视觉语言。
+- [ ] 目标 OSM 标签导致 lane-arrow GeoJSON 与移除这些标签的对照产生可观察差异。
+- [ ] 自定义 arrow properties 标识来源和 OSM way / direction / lane，便于诊断。
+- [ ] 纯 Node 测试覆盖标签解析、forward/backward、lane placement、组合转向和幂等排序。
+- [ ] 本地素材清单包含所有上游箭头，逐项标记 CC0 来源、支持状态和测试状态；未测试条目
+  不会参与生产映射。
+- [ ] 仅南台子完整链和质量门验证通过。
+- [ ] 无 Git 提交，直到用户明确确认。
+
+## Out Of Scope
+
+- 修改 osm2streets 依赖、道路改为 Cesium 直渲染、增加新的道路渲染图层。
+- 支持首版范围之外的 OSM maneuver 词汇、匝道标线、文字或自行车专用箭头。
+
+## Delivery Gate
+
+在自定义箭头接入生产 GeoJSON / Blender 导出前，用户必须确认 `right` 与
+`through;right` 样张的轮廓和视觉语言。

.trellis/tasks/08-04-add-osm-turn-lane-arrows/research/lane-icons.md

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+# lane-icons research
+
+Source: <https://github.com/openstreetmap/lane-icons>, inspected 2026-08-04.
+
+## Provenance
+
+- Owner: `openstreetmap` GitHub organization.
+- Repository tree revision: `db3cab321da93a757c2cf3cdb4f1f1db6b1a091c` (`master`).
+- License: `LICENSE.md` is CC0 1.0 Universal. Keep that text adjacent to any
+  vendored source assets.
+
+## Relevant Contents
+
+- `docs/through.svg`
+- `docs/left.svg`
+- `docs/left-through.svg`
+- `docs/slight_left.svg`
+- `docs/slight_left-through.svg`
+- `docs/sharp_left.svg`
+- `docs/sharp_left-through.svg`
+- `docs/reverse_left.svg`
+- `docs/reverse_left-through.svg`
+- `docs/reverse_left-left-slight_left-through.svg`
+- `docs/left-slight_left-through.svg`
+
+## Design Rules
+
+`DESIGN.md` bases arrows on the MUTCD Standard Arrow. It specifies a shared
+shaft for compound arrows, smooth curves, aligned arrow bottoms, and reduced
+arrowhead scale as the number of directions grows. The upstream SVGs are
+single-color and stroke-free; our existing render layer supplies the project
+fill and outline treatment.
+
+## Adoption Decision
+
+Vendor all listed arrow SVGs with provenance and CC0 license text. The
+production mapping is initially restricted to `through`, `left`, `right`,
+`through;left`, and `through;right`. Right-side variants are deterministic
+mirrors of upstream left-side assets. Every other vendored arrow remains
+explicitly untested and unavailable to the production mapper.

.trellis/tasks/08-04-add-osm-turn-lane-arrows/task.json

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+{
+  "id": "add-osm-turn-lane-arrows",
+  "name": "add-osm-turn-lane-arrows",
+  "title": "Add OSM turn lane arrows",
+  "description": "",
+  "status": "in_progress",
+  "dev_type": null,
+  "scope": null,
+  "package": null,
+  "priority": "P2",
+  "creator": "dingkang",
+  "assignee": "dingkang",
+  "createdAt": "2026-08-04",
+  "completedAt": null,
+  "branch": null,
+  "base_branch": "main",
+  "worktree_path": null,
+  "commit": null,
+  "pr_url": null,
+  "subtasks": [],
+  "children": [],
+  "parent": null,
+  "relatedFiles": [],
+  "notes": "",
+  "meta": {}
+}