No GPU→CPU fallback when separation fails #276

Location: separate.py
Severity: CRIT

One MPS/CUDA failure (OOM, unsupported op, driver hiccup) kills the whole job with the generic “Audio processing failed.” This is the Mac Mini report verbatim — the user needed a LaunchAgent env-var hack to force CPU. separate() raises on any non-zero demucs exit; runner._run_async marks error and deletes the job dir.
On failure with device != cpu, log the real stderr tail, retry once on CPU, and surface a “ran on CPU (slower)” note. Mirrors the #247 lesson on the runtime path.

From the health report. Part of #273 (Phase 2 — Resilience).