docs: CUDA worker setup guide (T490s + 2080Ti eGPU on tailnet)

Ready-to-follow checklist for standing up a headless Linux + eGPU CUDA node to
offload the CUDA-only 3D/mocap jobs the Mac can't run (splat->mesh, GVHMR mocap).
Bare-metal Linux required (no VM GPU passthrough on Mac hosts). Planned remote-CUDA
operators: sugar_mesh, gvhmr_mocap.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/CUDA-WORKER.md

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+# CUDA Worker Setup — T490s + 2080 Ti eGPU on the tailnet
+
+Goal: a headless Linux box with the RTX 2080 Ti (11GB) eGPU, live on Tailscale, that
+MODELBEAST (on the M3 Ultra) offloads the CUDA-only jobs the Mac can't run —
+gaussian-splat → mesh extraction (SuGaR/2DGS), research-grade video mocap
+(GVHMR/WHAM/TRAM), NeRF/tiny-cuda-nn, nvdiffrast/PyTorch3D.
+
+**Why a ThinkPad and not the Intel iMac:** no T2 chip = no Secure-Boot/Thunderbolt
+fight; laptop idles ~6–10W (+ ~20W eGPU) vs ~55–75W for the iMac; battery = built-in
+UPS. The 2080 Ti is EOL-ish (Turing: no bf16/fp8, 11GB) — it's a *compatibility*
+box, not a performance one. It will not beat the M3 Ultra at anything the Mac
+already does; it only unlocks the CUDA-locked tail.
+
+## Do this at the shop (once)
+
+1. **Ubuntu 24.04 LTS**, bare metal (dual-boot Win11 or wipe — bare-metal, NOT a VM;
+   macOS/Windows hypervisors can't pass a physical GPU through, so a Linux VM can't
+   do CUDA on the eGPU).
+
+2. **Thunderbolt authorize the eGPU** (plug in the Razer Core first):
+   ```bash
+   sudo apt install bolt
+   boltctl list                      # find the enclosure UUID
+   boltctl enroll --policy auto <UUID>
+   ```
+
+3. **NVIDIA driver + CUDA:**
+   ```bash
+   sudo ubuntu-drivers autoinstall   # or the latest official driver branch
+   sudo apt install nvidia-cuda-toolkit
+   sudo reboot
+   nvidia-smi                        # must list the 2080 Ti over Thunderbolt
+   ```
+   If it doesn't appear: confirm the eGPU was connected at boot, re-check `boltctl`,
+   ensure the `thunderbolt` module loads before `nvidia_drm`.
+
+4. **Tailscale:**
+   ```bash
+   curl -fsSL https://tailscale.com/install.sh | sh
+   sudo tailscale up --ssh          # --ssh lets the M3 Ultra SSH in over the tailnet
+   tailscale ip -4                   # note this IP → put it in MODELBEAST settings
+   ```
+
+5. **Headless / low-power:** run lid-closed →
+   `sudo sed -i 's/#HandleLidSwitch=suspend/HandleLidSwitch=ignore/' /etc/systemd/logind.conf`
+   then `sudo systemctl restart systemd-logind`. Enable Wake-on-LAN in BIOS + `ethtool`
+   if you want it to sleep and wake on demand.
+
+## MODELBEAST integration (I'll build this when the box exists)
+
+The operator framework already shells out to tools; a **remote-CUDA operator** wraps
+that pattern: rsync the input to `cuda_host:~/work/`, `ssh cuda_host` to run the CUDA
+tool in its venv, rsync results back, register as assets. Planned operators:
+- `sugar_mesh` — splat `.ply` → textured mesh (closes the Brush→mesh gap; the Mac can't extract meshes from splats).
+- `gvhmr_mocap` — video → world-grounded SMPL → FBX (research-grade, replaces the cloud/manual path).
+
+Add a `cuda_host` setting (the tailnet IP + user) to the vault so these operators know where to reach it. Fits in 11GB: SuGaR/2DGS/gsplat (~5-6GB), GVHMR/WHAM (light). Does NOT fit: FLUX, 20B+ models — those stay on the Mac.
+
+## Reality check
+Only worth it because the card's already owned. If you were buying, a used RTX 3090
+(24GB, bf16) would be strictly better and unlock FLUX/video too. Turing's runway is
+shrinking (newer 3D wheels drop 20-series), so treat this as "use the free card for
+the CUDA-only leftovers," not a long-term foundation.