Refactor fountain assembly module

.trellis/spec/blender/module-structure.md

@@ -50,7 +50,8 @@
 | `mesh.py` | bpy | `MeshBatch`、`make_prism`、`add_roof`、`add_wall_panel`、`add_polyline`、集合管理 |
 | `materials.py` | bpy | 把 `catalog` 的规格变成真实材质：`from_spec()`、贴图、程序化噪声、tint、alpha-clip |
 | `tree.py` | bpy | 两个 vendored 模型 → 一套可实例化的运行时形状 |
-| `water.py` / `grass.py` / `scrub.py` | bpy | 单一 OSM 要素的装配 |
+| `water.py` / `grass.py` / `scrub.py` | bpy | 单一 OSM 面要素的装配 |
+| `fountain.py` | bpy | 单一 OSM 点要素 `amenity=fountain` 的装配 |
 
 ### `geom.py` 的两条隐含约定
 
@@ -62,7 +63,7 @@
 
 ## 要素模块的统一形状
 
-`water.py` / `grass.py` / `scrub.py` 三个要素模块签名一致：
+`water.py` / `grass.py` / `scrub.py` 三个面要素模块签名一致：
 
 ```python
 def assemble(ring, [way_id,] scene_xmin, scene_xmax, scene_ymin, scene_ymax,
@@ -83,6 +84,17 @@ def assemble(ring, [way_id,] scene_xmin, scene_xmax, scene_ymin, scene_ymax,
    的 `focus`）
 4. **不自己找数据**。ring 由 `generate_scene.py` 传入，模块只负责装配
 
+`fountain.py` 是点要素模块，不收 ring 或裁剪边界：
+
+```python
+def assemble(name, x, y, collection, materials):
+    ...
+```
+
+`generate_scene.py` 仍负责过滤 `amenity=fountain`、检查点是否在范围内、投影坐标、
+创建三张 fountain 材质，并维护 `counts["fountain_count"]`。模块只负责在已投影
+坐标上创建 basin / water / pedestal / spray objects，保持对象名和自定义属性不变。
+
 ### 加一种新 OSM 要素
 
 目标形态：**新增一个模块 + 注册一行，不改 `build()`**。

.trellis/spec/guides/artifact-parity-guide.md

@@ -163,7 +163,7 @@ capturedAt / durationMs / label
 |---|---|---|
 | P0 | 抽纯函数到 `osmassets/{osm,geom}.py` | ✅ 已完成 |
 | P1 | `catalog.py` 单一定义源 + `check_layers` | ✅ 已完成 |
-| P2 | 要素注册表 | ⚠️ **部分**——`water/grass/scrub/tree.py` 已拆出，但**没有 `features/` 注册表**，`building` / `fountain` / `roads` 仍在 `generate_scene.py` 里 |
+| P2 | 要素注册表 | ⚠️ **部分**——`water/grass/scrub/tree/fountain.py` 已拆出，但**没有 `features/` 注册表**，`building` / `roads` 仍在 `generate_scene.py` 里 |
 | P3 | 材质契约化（自定义属性传递 spec） | ✅ 已完成——`catalog.MATERIALS[*]["cesium"]` 经 `materials.from_spec()` 写入 `material["cesium_export"]`，`export_cesium.py` 优先读该属性；四张材质名表仅作旧 `.blend` 回退 |
 
 ### 已知缺陷（记录在案，本轮不修）

.trellis/tasks/08-03-extract-fountain-module/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/08-03-extract-fountain-module/design.md

@@ -0,0 +1,53 @@
+# Design
+
+## Architecture
+
+`fountain.py` will join the existing bpy-layer feature modules under
+`blender/osmassets/`. It may import `bpy`, `math`, and the collection helper
+needed to preserve current object linking behavior.
+
+The module will expose one function:
+
+```python
+def assemble(name, x, y, collection, materials):
+    ...
+```
+
+The signature mirrors the existing inline `add_fountain(name, x, y, collection,
+materials)` call site to keep the migration mechanical and parity-friendly.
+
+## Boundaries
+
+- `generate_scene.py` keeps OSM feature filtering, projection, material creation,
+  and count ownership.
+- `fountain.py` owns only Blender object creation for one fountain at already
+  projected `(x, y)` coordinates.
+- No pure-Python module may import `bpy`; this module is explicitly in the
+  bpy layer, like `water.py`, `grass.py`, `scrub.py`, and `tree.py`.
+
+## Data Flow
+
+1. `generate_scene.py` creates `fountain_mats` from `catalog.MATERIALS`.
+2. `generate_scene.py` finds point features where `tags.amenity == "fountain"`.
+3. `Projector.xy()` converts the OSM coordinate to local meters.
+4. `fountain.assemble("Fountain_" + id, fx, fy, props_c, fountain_mats)` creates
+   the existing basin, water disk, pedestal, crown, and droplets.
+5. `generate_scene.py` increments `counts["fountain_count"]`.
+
+## Compatibility
+
+The refactor must preserve all generated object names, primitive dimensions,
+materials, smoothing flags, and custom properties. Cesium export reads the
+resulting `.blend`; it should see an equivalent scene graph.
+
+## Trade-Offs
+
+A full feature registry is intentionally deferred. Starting with a one-module
+extraction keeps the diff small and lets parity isolate any regression to the
+fountain move before higher-risk building or road work.
+
+## Rollback
+
+Rollback is straightforward: remove `fountain.py`, restore the inline
+`add_fountain()` function, remove the module import, and restore the original
+call site.

.trellis/tasks/08-03-extract-fountain-module/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/08-03-extract-fountain-module/implement.md

@@ -0,0 +1,40 @@
+# Implementation Plan
+
+## Checklist
+
+1. Capture a parity baseline before product-code edits.
+2. Add `blender/osmassets/fountain.py` with the current fountain assembly logic.
+3. Import the module in `blender/generate_scene.py`.
+4. Remove inline `add_fountain()` from `generate_scene.py`.
+5. Replace the call site with `fountain.assemble(...)`.
+6. Run Python validation:
+   - `python3 -m py_compile blender/osmassets/fountain.py`
+   - `python3 -m py_compile blender/generate_scene.py`
+   - `python3 -m unittest blender/tests/test_pure.py`
+7. Capture parity after the refactor.
+8. Compare before/after parity snapshots and inspect any non-ignored diff.
+9. Update `.trellis/spec` or `docs/changelog.md` only if the work reveals a
+   durable new constraint or user-visible change.
+10. Commit, archive the task, and record the journal entry.
+
+## Validation Commands
+
+```bash
+node scripts/parity.js capture fountain-module-before --stages blender,cesium
+python3 -m py_compile blender/osmassets/fountain.py
+python3 -m py_compile blender/generate_scene.py
+python3 -m unittest blender/tests/test_pure.py
+node scripts/parity.js capture fountain-module-after --stages blender,cesium
+node scripts/parity.js compare fountain-module-before fountain-module-after
+```
+
+## Risk Points
+
+- `link_object_to_collection()` must be used the same way as before so object
+  collection membership stays unchanged.
+- The basin custom property must remain on the basin object only.
+- Droplet order and names must stay stable.
+- `math` usage may move with the function; remove the import from
+  `generate_scene.py` only if no remaining code uses it.
+- Parity is mandatory because this is a pure refactor of bpy-layer scene
+  generation.

.trellis/tasks/08-03-extract-fountain-module/prd.md

@@ -0,0 +1,73 @@
+# Extract fountain module
+
+## Goal
+
+Move the fountain assembly code out of `blender/generate_scene.py` into a
+dedicated bpy-layer module, keeping the generated `.blend` / `.glb` structure
+unchanged. This is the first low-risk step toward the documented P2 feature
+module / registry direction.
+
+## Background
+
+- `.trellis/spec/guides/artifact-parity-guide.md` records P2 as partial:
+  `water.py`, `grass.py`, `scrub.py`, and `tree.py` exist, but `building`,
+  `fountain`, and `roads` still live in `generate_scene.py`.
+- `blender/generate_scene.py:639` defines `add_fountain()` inline.
+- `blender/generate_scene.py:895` dispatches OSM point features with
+  `amenity=fountain`, calls `add_fountain("Fountain_" + id, ...)`, and
+  increments `counts["fountain_count"]`.
+- `blender/osmassets/catalog.py` already owns the three fountain materials:
+  `fountain_stone`, `fountain_water`, and `fountain_spray`.
+- This task is a pure refactor. It must not change fountain geometry, object
+  names, materials, custom properties, counts, stdout markers, or Cesium export
+  behavior.
+
+## Requirements
+
+1. Add a new bpy-layer module at `blender/osmassets/fountain.py`.
+2. Move the current fountain assembly behavior from `generate_scene.py` into
+   the new module.
+3. Keep `generate_scene.py` responsible for:
+   - creating fountain materials from `catalog.MATERIALS`;
+   - filtering `point_features` for `amenity=fountain`;
+   - projecting coordinates;
+   - incrementing `counts["fountain_count"]`.
+4. Preserve the existing object names:
+   - `Fountain_<id>_Basin`
+   - `Fountain_<id>_Water`
+   - `Fountain_<id>_Pedestal`
+   - `Fountain_<id>_Water_Crown`
+   - `Fountain_<id>_Droplet_<n>`
+5. Preserve the existing basin custom property:
+   `osm_feature = "amenity=fountain"`.
+6. Do not introduce a full `features/` registry in this task.
+7. Do not modify `building`, `roads`, material definitions, `MATERIALS` order,
+   `ROAD_LAYERS` order, stdout markers, or parity ignore lists.
+8. Do not fix unrelated documented defects D1, D2, or D3.
+
+## Acceptance Criteria
+
+- [x] `blender/osmassets/fountain.py` contains the fountain assembly behavior
+      and imports only bpy-layer-safe dependencies.
+- [x] `blender/generate_scene.py` imports and calls the new fountain module;
+      no inline `add_fountain()` function remains there.
+- [x] Scene counts and `SCENE_DONE` JSON keys remain unchanged.
+- [x] `python3 -m unittest blender/tests/test_pure.py` passes.
+- [x] `python3 -m py_compile blender/osmassets/fountain.py` passes.
+- [x] `python3 -m py_compile blender/generate_scene.py` passes.
+- [x] A before/after parity comparison is run for the Blender/Cesium stages and
+      any non-ignored diff is either absent or explicitly explained as
+      expected. For this refactor, the expected result is no contract diff.
+
+## Out Of Scope
+
+- Full feature registry design or implementation.
+- Building extraction.
+- Road extraction.
+- Fountain visual redesign or geometry changes.
+- Material contract changes.
+- Documentation-only cleanup of stale comments such as D3.
+
+## Open Questions
+
+None.

.trellis/tasks/08-03-extract-fountain-module/task.json

@@ -0,0 +1,26 @@
+{
+  "id": "extract-fountain-module",
+  "name": "extract-fountain-module",
+  "title": "Extract fountain module",
+  "description": "",
+  "status": "in_progress",
+  "dev_type": null,
+  "scope": null,
+  "package": null,
+  "priority": "P2",
+  "creator": "dingkang",
+  "assignee": "dingkang",
+  "createdAt": "2026-08-03",
+  "completedAt": null,
+  "branch": null,
+  "base_branch": "main",
+  "worktree_path": null,
+  "commit": null,
+  "pr_url": null,
+  "subtasks": [],
+  "children": [],
+  "parent": null,
+  "relatedFiles": [],
+  "notes": "",
+  "meta": {}
+}