Blender 5.2.2 LTS on fv-ml1 GPU 3, on demand. Agents drive it; there is also a browser desktop to watch it or take over. Prime, 2026-09-27: "go ahead with gpu 3, both". He does not use Blender himself, so the agent side (MCP) is the primary interface.


Desktop	`https://10.251.50.54:3001` (self-signed cert). Basic auth: user `blender`, password `secret get fv-ml1/blender-web-password`.
Image	`lscr.io/linuxserver/blender:5.2.2-ls241@sha256:9216c77a…` (Selkies 2.0 Wayland desktop, NVENC stream).
GPU	GPU 3 only (`NVIDIA_VISIBLE_DEVICES=3`). About 270 MiB is held while the desktop runs.
Files	`/work` → `/tank/blender` (projects, assets, renders; not backed up). `/config` → `/opt/docker/data/blender` (prefs, add-ons; restic). Files are owned by infra-ops (uid 1002), so agents can `scp` in and out.

⚠ On demand: GPU 3 is borrowed

GPU 3 is the fleet's reserve card for a full-size vLLM seat (servers/fv-ml1/README.md). Blender uses it only while in use:

ssh infra-ops@10.251.50.54 'cd /opt/docker/compose/blender && docker compose up -d'   # start
ssh infra-ops@10.251.50.54 'cd /opt/docker/compose/blender && docker compose down'    # stop, card back to 0

restart: "no", so a reboot never brings it back. When a big seat moves onto GPU 3, Blender stays down.

Headless rendering (no desktop needed)

ssh infra-ops@10.251.50.54 'docker exec -u abc blender blender -b /work/<file>.blend -E CYCLES -o /work/out/frame_#### -a -- --cycles-device OPTIX'

Run as -u abc, the image's user, mapped to uid 1002, so outputs land owned by infra-ops.

Acceptance (2026-09-27, 1356)

Cycles sees the card on both OptiX and CUDA: "NVIDIA RTX PRO 6000 Blackwell Max-Q Workstation Edition". The build ships kernel_sm_120.cubin plus OptiX PTX.
Self-test (/tank/blender/render_test.py): a subdivided glass monkey, 1920×1080, 1024 samples, 32 bounces, no denoise. OptiX 3.54 s against CPU 22.71 s (96 threads). That is n=1 per device: a functional check that the GPU is really used, not a benchmark. A trivial default-cube scene could not separate them (0.59 s against 0.65 s), which is why the self-test scene is heavy.
Web auth: no credentials gives 401, a wrong password 401, the right one 200.
Selkies: "Render node 1 encodes H264, AV1, H265 on nvenc"; the Wayland renderer runs GL on GPU 3.

Agent control (MCP): `scripts/blender-mcp`

The chosen server is mcp-for-blender (MIT, one maintainer, ~29k stars; researched by dvalin-smithy-dev 2026-09-27, thread 01M3JA61FTFW2ZPSD20MHF7RPJ, full note in dvalin-smithy research/blender-agent-drive-2026-09-27.md). Two halves:

The add-on is inside the running GUI Blender and serves a socket that executes arbitrary Python with no authentication. It is vendored at upstream commit 41a18432 (conf/scripts/addons/blender_mcp.py, MIT licence alongside) and started by conf/scripts/startup/fleet_mcp.py. The add-on only serves from a GUI Blender, never from blender -b, which is one reason the desktop exists.
The MCP server: mcp-for-blender==2.1.1, frozen in conf/mcp-requirements.txt and installed in /work/.mcp-venv inside the container (scripts/blender-mcp setup). Agents reach it as stdio over ssh infra-ops@fv-ml1 docker exec -i. It runs in the container for two reasons:
1. No port is published. The socket stays on the container's localhost, so access means ssh + docker on fv-ml1.
2. Viewport screenshots need a shared filesystem. Blender writes the image and the server reads it back. With the server on nh3-dev it failed ("Screenshot file was not created").

Settings: DISABLE_TELEMETRY=true and BLENDER_MCP_SAFE_MODE=1. Safe mode puts upstream's AST allowlist in front of execute_blender_code: bpy, bmesh, mathutils and pure stdlib only, and no os, open, eval or network. It guards against prompt injection from third-party asset text; it is not a sandbox.

For an agent

scripts/blender-mcp up          # GPU 3 is borrowed: start only when needed
scripts/blender-mcp status      # wait for "mcp add-on: answering" (~10-40 s)
claude mcp add blender -- /home/lkraven/development/eshpfi-management/scripts/blender-mcp   # PER TASK (Prime 2026-09-27): never user/project-wide
scripts/blender-mcp down        # when finished: the card goes back to 0

Always pass user_prompt. The tools require it; it is a short statement of the user's request.
Render on the GPU: set scene.cycles.device = 'GPU' on any scene you create. Safe mode forbids touching bpy.context.preferences, so the startup hook has already pointed Cycles at OptiX on GPU 3. The startup scene is already set to GPU.
Save everything under /work/… (= fv-ml1:/tank/blender), then scp it out.
Look before you report: get_viewport_screenshot returns an image, and a still render to /work is the real check.
The asset tools (Poly Haven etc.) reach the internet from Blender. The paid ones (Hyper3D, Hunyuan, Tripo, Sketchfab) need keys we do not have; leave them off.

Acceptance (2026-09-27, 1433)

An MCP client on nh3-dev → scripts/blender-mcp → the in-container server → the add-on:

initialize OK; 36 tools listed.
execute_blender_code built a gold metallic torus and rendered it with Cycles on the GPU to /work/_selftest/mcp-torus.png. The file landed, and I checked it by eye.
get_viewport_screenshot returned an image of the scene.
Negative control: import os was rejected by safe mode.
status pings the add-on itself. A TCP probe was useless because the port accepted while Blender was still loading.

⚠ Two traps found on the way, both fixed and commented where they live:

Enabling the add-on from a startup script gets undone when user prefs load. The hook enables it in a timer instead.
A pre-flight ssh without -n swallowed the MCP client's initialize, and the session hung at init.

README.md Unescape Escape

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