Refactor Cesium material export contract

.trellis/tasks/08-03-material-export-contract/task.json

@@ -0,0 +1,33 @@
+{
+  "id": "material-export-contract",
+  "name": "material-export-contract",
+  "title": "Material export contract",
+  "description": "Move Cesium material export overrides from export_cesium.py name tables into catalog-backed material contracts saved on Blender materials.",
+  "status": "in_progress",
+  "dev_type": "refactor",
+  "scope": "blender",
+  "package": "blender",
+  "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": [
+    "blender/osmassets/catalog.py",
+    "blender/osmassets/materials.py",
+    "blender/export_cesium.py",
+    ".trellis/spec/blender/module-structure.md",
+    ".trellis/spec/blender/asset-generation.md",
+    ".trellis/spec/guides/artifact-parity-guide.md"
+  ],
+  "notes": "Complex task. Planning artifacts must be reviewed before task.py start; preserve old .blend export fallback and validate with unittest plus parity evidence.",
+  "meta": {}
+}