docs: record usd-core decision, add Dockerfile task 1.0

- Mark USD library question as decided: usd-core>=24.11 (pxr module)
- Add Task 1.0 to USD implementation plan: Dockerfile install step
- Add usd-core to Priority 2 file targets in ROADMAP

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

ROADMAP.md

@@ -92,6 +92,7 @@ This priority combines dead-code deletion and task decomposition because both ar
 
 | Action | Path |
 |---|---|
+| ADD pip install | `render-worker/Dockerfile` — `usd-core>=24.11` (provides `pxr` module) ✅ decided |
 | CREATE | `render-worker/scripts/export_step_to_usd.py` — XCAF → USD, hierarchy + metadata + partKey |
 | ADD enum value | `backend/app/domains/media/models.py` — `usd_master` to `MediaAssetType` |
 | CREATE migration | `backend/alembic/versions/060_usd_master_asset_type.py` |

docs/plans/0001-step-to-usd-implementation.md

@@ -9,7 +9,7 @@
 ## Prerequisites
 
 - [ ] Priority 1 complete (step_tasks.py decomposed, blender_render.py decomposed)
-- [ ] Decision: USD authoring library (see Open Questions below)
+- [x] Decision: USD authoring library → **`usd-core` (pip)** — provides `pxr` module, no GPU tools needed, pip-installable in render-worker
 - [ ] Decision: seam/sharp payload encoding (primvars vs. JSON sidecar)
 
 ---
@@ -18,6 +18,21 @@
 
 **Goal:** Export a valid `usd_master` alongside the existing GLB pipeline without changing any browser behavior.
 
+### Task 1.0 — Install `usd-core` in render-worker
+
+**File:** `render-worker/Dockerfile`
+
+```dockerfile
+# OpenUSD Python bindings — provides pxr module for USD authoring
+RUN pip3 install --no-cache-dir "usd-core>=24.11"
+```
+
+Add after the `gmsh` line. `usd-core` is the Pixar-maintained pip distribution of OpenUSD — no GPU, no USD imaging, just the core authoring/scene APIs (`pxr.Usd`, `pxr.UsdGeom`, `pxr.Sdf`, `pxr.Vt`).
+
+**Acceptance gate:** `docker compose exec render-worker python3 -c "from pxr import Usd; print(Usd.GetVersion())"` → `(24, 11, 0)` or later.
+
+---
+
 ### Task 1.1 — `export_step_to_usd.py` scaffolding
 
 **File:** `render-worker/scripts/export_step_to_usd.py`
@@ -304,11 +319,10 @@ Clicking an unassigned part in the viewer auto-focuses it in the MaterialPanel.
 
 | # | Question | Options | Default recommendation |
 |---|---|---|---|
-| 1 | USD authoring library | `pxr` (full OpenUSD, heavy) / `usda` text templating (no deps) / `usd-core` pip | Start with `pxr` — pip-installable, same OCC kernel available |
+| 1 | USD authoring library | ~~`pxr` full / `usda` text / `usd-core` pip~~ | ✅ **`usd-core` pip** — `pip install usd-core` in render-worker Dockerfile |
 | 2 | Seam/sharp payload encoding | Custom primvars on mesh prim / separate JSON sidecar / GLB extras (current) | Index-space primvars — cleaner, survives transforms |
 | 3 | Preview GLB derivation | USD → GLB export pass / co-author from same tessellation pass | Co-author during migration (avoid round-trip loss) |
 | 4 | Single-file USD or override layers | Flat single file / canonical + overlay layers (flattened for delivery) | RFC recommends Option B (overlay layers, flatten for delivery) |
-| 5 | `pxr` install in render-worker | Add to `render-worker/Dockerfile` / use system package | `pip install usd-core` — no NVIDIA/Pixar GPU tools needed |
 
 ---