Step 1 of the LongCat-Video integration: provision the runtime. No engine code yet.

LongCat is the strictest isolation in the tree — it pins Python 3.10, torch 2.6+cu124,
transformers 4.41 and numpy 1.26 against the main venv's 3.13 / 2.11+cu130 / 5.x / 2.4,
four simultaneous conflicts, plus opencv-python against the bundled opencv-contrib.
Installing it into the main venv would walk transformers and numpy backwards and break
the stack, the failure already recorded for parler-tts.

Crucially, coderai cannot build this venv itself: every venv bootstrap in codai/ uses
`sys.executable -m venv`, which is 3.13. The only 3.10 in the tree is the standalone
interpreter hand-built for the lip-sync tools and bundled as py310/, so LongCat rides
that same interpreter in a venv of its own (its torch differs, so they cannot share one).

- requirements-longcat.txt: upstream's pins off the cu124 index. flash-attn is
  deliberately NOT pinned — it is a source build needing ninja and a CUDA toolchain, and
  upstream accepts xformers, which ships a wheel; longcat.attention = "flash" is the
  opt-in. streamlit (upstream's demo UI) is left out.
- build_oci_image.sh: declares LONGCAT_VENV and bundles it. The py3.10 interpreter is now
  discovered from EITHER py3.10 venv's pyvenv.cfg — it was read only from the lip-sync
  one, so a host with LongCat and no lip-sync venv would have bundled a venv with no
  interpreter to run it.
- Dockerfile.oci-venv: copies longcat_venv and the pyvenv.cfg/bin-symlink rewrite now
  loops over both venvs. A bundled venv still carries the build host's `home =`, so
  without that its bin/python points at an interpreter the image does not have.
- smoke_test_services.sh: asserts 3.10 + torch 2.6 + transformers 4.41, not just that
  torch imports — a venv re-pointed at the WRONG interpreter passes a bare import while
  being useless.
- LongcatConfig (enabled, service_url, venv, python, auto_build, host, port, gpu,
  attention, ready_timeout, extra_args, extra_env), attached to Config, serialised by
  save_config, reconstructed in load() and exposed/parsed by the admin settings API.
  auto_build ships OFF: it pulls torch 2.6 plus its CUDA runtime.

16 tests. The config round-trip one caught a real hole: load() reconstructs each section
explicitly, so without its line the operator could set LongCat up in the interface and
lose it on the next restart.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0182DhR1eFNPQyGmDrpHbedY