H3 and Krea 2 need diffusers >= 0.40 while the server runs 0.38. Upgrading in
place is not free: measured on this box, SDXL comes out bit-identical but Z-Image
drifts (mean |diff| 0.0146, max 0.32, against a same-version control that is
bit-identical) — so the upgrade would silently change image output for a model
that is working fine.

Since diffusers is imported once per process, the split only has to be
per-process. The H3 venv is now created with --system-site-packages and given
nothing but diffusers>=0.40 and huggingface_hub>=1.23; torch, transformers and the
rest are inherited from the server's venv. That is 75 MB instead of the several GB
a standalone venv costs, and keeps one torch on the machine.
CODERAI_H3_STANDALONE_VENV=1 still builds a fully independent venv from
requirements-h3.txt, for the day the parent's torch is too old.

Training follows the same boundary: tools/lora_train_worker.py runs one job in the
overlay — re...