ace-step + stable-audio-open: deploy music + SFX generation to irv-ml1

Two new audio-generation stacks alongside the TTS slate:

ace-step :8210 — Apache 2.0 music generation foundation model
(hybrid diffusion + LLM). Lyric-aware multi-minute songs. ~10-12 GB
VRAM during inference, A6000-pinned. Custom Dockerfile patches
upstream's torch/cu126 resolution bug (--extra-index-url cu126 was
falling back to pypi-default cu13 wheels, mismatching torchvision).

stable-audio-open :8211 — Stability AI 1.21B latent-diffusion SFX +
ambience. Up to 47s clips at 44.1 kHz. ~6 GB VRAM in fp16,
A6000-pinned. Custom FastAPI shim around diffusers' StableAudioPipeline
(no upstream HTTP server). Dockerfile pins torchsde explicitly —
diffusers doesn't pull it as a hard dep but
CosineDPMSolverMultistepScheduler needs it.

stacks/stable-audio-open/README.md

@@ -0,0 +1,55 @@
+# stable-audio-open
+
+Stability AI's Stable Audio Open 1.0 — text-to-audio latent diffusion.
+Strong on SFX, foley, ambience, short loops. Not a music model — it
+does not generate intelligible vocals or structured songs (use
+`ace-step` for that).
+
+| | |
+|---|---|
+| host | `irv-ml1` |
+| port | `8211` |
+| GPU | A6000 (`device_ids: ["1"]`) |
+| VRAM | ~6 GB in fp16 |
+| max clip | 47 s at 44.1 kHz |
+| upstream | https://github.com/Stability-AI/stable-audio-tools |
+| model | `stabilityai/stable-audio-open-1.0` (gated) |
+| license | Stability AI Community (non-commercial / personal / research) |
+
+## API surface
+
+`server.py` (custom FastAPI shim) exposes:
+
+- `GET /health` — returns 200 once the model is loaded.
+- `POST /v1/audio/sfx` — returns a `audio/wav` blob.
+
+```jsonc
+{
+  "prompt": "a vintage typewriter clacking in a quiet room",
+  "negative_prompt": "Low quality.",   // optional, default "Low quality."
+  "duration": 10.0,                     // seconds, 0.5 – 47
+  "steps": 100,                         // 10 – 300, more = better quality
+  "seed": 42,                           // optional
+  "cfg_scale": 7.0                      // 0 – 20
+}
+```
+
+Why a custom shim: there's no upstream Docker image and no upstream
+HTTP server for Stable Audio Open. Diffusers exposes
+`StableAudioPipeline` cleanly — the shim is ~70 lines.
+
+## Deploy
+
+```bash
+scripts/elway irv-ml1 --playbook playbooks/deploy-stable-audio-open.yaml
+```
+
+Pre-deploy: visit https://huggingface.co/stabilityai/stable-audio-open-1.0
+once and accept the Community License (HF token alone is not enough —
+the gate is per-model). Then put the token in `SAO_HF_TOKEN` in `.env`
+on the host.
+
+## Tunables
+
+See `.env.example` — copy to `.env` on the host (lives at
+`/opt/docker/compose/stable-audio-open/.env`, gitignored).