Self-restart worker process when model loading fails

Discovered vibevoice sitting at 3.2GB resident GPU memory with
loaded_models: [] and no idle-unload ever firing for it again. Root cause:
a load attempt had OOM'd partway through (competing with an unrelated
ollama process on the same GPU), so _MODEL_CACHE was never populated —
the idle-unload loop only clears that cache, so it had nothing to act on,
even though the partially-constructed model had already left memory
allocated. gc.collect()+empty_cache() don't reliably reclaim memory from
an interrupted from_pretrained() call.

Confirmed a plain process restart does fully reclaim it, so each worker
now treats any load failure as fatal: log it and os._exit(1), letting
supervisord's autorestart=true respawn a clean process immediately.
Verified with a bogus model id — worker exits, respawns, and passes the
smoke test right after.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

app/asr/workers/faster_whisper_worker.py

@@ -167,12 +167,23 @@ def _load_model(model_name: str) -> WhisperModel:
         if _MODEL_CACHE:
             # Only one whisper model resident at a time — switching sizes frees the old one.
             _unload_whisper_models()
-        _MODEL_CACHE[model_name] = WhisperModel(
-            model_name,
-            device=DEVICE,
-            compute_type=COMPUTE_TYPE,
-            download_root=str(MODEL_CACHE),
-        )
+        try:
+            _MODEL_CACHE[model_name] = WhisperModel(
+                model_name,
+                device=DEVICE,
+                compute_type=COMPUTE_TYPE,
+                download_root=str(MODEL_CACHE),
+            )
+        except Exception as e:
+            # A load interrupted partway (e.g. OOM) can leave CUDA memory
+            # fragmented/leaked in ways gc.collect()+empty_cache() don't
+            # reliably reclaim, and since _MODEL_CACHE never got populated
+            # the idle-unload loop has nothing to clean up either.
+            # Restarting the whole process is the only guaranteed way to get
+            # that memory back — supervisord's autorestart=true respawns it
+            # immediately.
+            print(f"[faster_whisper] model load failed, restarting process to reclaim GPU memory: {type(e).__name__}: {e}", flush=True)
+            os._exit(1)
     return _MODEL_CACHE[model_name]