# Blender: headless and agent-driven 3D on fv-ml1 GPU 3

**Blender 5.2.2 LTS** (bundled Python 3.13), runs on **fv-ml1 GPU 3** (RTX PRO 6000 Blackwell,
96 GB). Stack and full notes: `/home/lkraven/development/eshpfi-management/stacks/blender/README.md`.

⚠ **GPU 3 is borrowed.** It is the fleet's reserve card for a full-size vLLM seat. Blender
runs only while in use, and this access ends if a big seat moves onto the card.

## Two ways in

| You are… | Use | Shape |
|---|---|---|
| a script or CLI caller (renders, conversions) | `scripts/blender-run` | one-shot `docker run --rm`: no desktop, gone when Blender exits |
| an agent building scenes interactively | `scripts/blender-mcp` (MCP, per task) | a GUI Blender plus the mcp-for-blender add-on; `up` / `status` / `down` |

Both scripts are in `/home/lkraven/development/eshpfi-management/scripts/` and run from nh3-dev,
reaching fv-ml1 as `infra-ops@10.251.50.54` over ssh. **No HTTP API** and no openapi.json.

## blender-run (headless)

```sh
scripts/blender-run --job /path/to/jobdir -- --python render.py -- out.png
scripts/blender-run -- --python-expr 'import bpy; print(bpy.app.version_string)'
```

- Always adds `-b --factory-startup --python-exit-code 1`. Arguments go after `--`.
- **Files:** fv-ml1 does not mount `/mnt/smithy`. `--job DIR` mirrors DIR to
  `fv-ml1:/tank/blender/jobs/<basename>-<hash of DIR's absolute path>/`, runs with that as
  the working directory, and copies new or changed files back into DIR. Nothing is ever
  deleted locally, and a rerun starts from an exact mirror, never from leftovers. Use
  relative input paths inside the job. Do not run the same DIR twice at once.
- **Engines headless (tested 2026-09-28):** Cycles on GPU (OptiX/CUDA), Cycles on CPU, EEVEE
  (EGL, no display needed, ~9 s with the shader compile on first use), Workbench. In 5.2 the
  EEVEE id is `BLENDER_EEVEE` (`BLENDER_EEVEE_NEXT` is gone). For Cycles GPU, set
  `prefs.compute_device_type = 'OPTIX'` and enable the OPTIX devices, then
  `scene.cycles.device = 'GPU'`. Factory startup defaults to CPU.
- **Import:** STL is built in (`bpy.ops.wm.stl_import`). **No STEP importer** is installed or
  built in.
- **Budget:** each run is capped at 64 GB RAM and 48 CPUs, with up to the whole 96 GB of VRAM.
  Keep to about 2 concurrent renders. It is not on irv-ml1, so irv-ml1's working-set budget
  does not apply.

⚠ **Foot-guns** (all measured):
- A `--python` script that raises exits **0** unless `--python-exit-code` is set. blender-run
  sets it.
- `render.filepath` must be **absolute**. Blender does not resolve a relative output path
  against the working directory ("cannot save 'out.png'"). Importers and Python file I/O do.
- Harmless stderr noise: "HIPEW initialization failed" (the AMD backend probing), and "Failed to
  create secure directory (/defaults): Operation not permitted" (the image's runtime-dir setup
  running as a non-root user; reported by draupnir 2026-09-28).
- The first OptiX render in a process includes about 1-2 s of kernel load.

## blender-mcp (agents)

Register it **per task**, never user- or project-wide (Prime, 2026-09-27):
`claude mcp add blender -- /home/lkraven/development/eshpfi-management/scripts/blender-mcp`.
Then run `scripts/blender-mcp up`, wait for `status` to say answering, work, and run `down`
when finished. Safe mode is on (no os/open/network in agent code), so the startup hook has
already pointed Cycles at OptiX. Save to `/work/…`. Details and traps are in the stack README.