Upgrade async GPU analysis and workbench UX

backend/app/services/segmentation_adapter.py

@@ -61,6 +61,41 @@ class _UltralyticsSegmentationAdapterBase:
                 message="Segmentation dependencies are not installed. Install backend optional extras with geointel-backend[ai].",
                 status_code=503,
             )
+        self.validate_runtime()
+
+    def validate_runtime(self) -> None:
+        """Fail closed when the deployment contract requires NVIDIA CUDA.
+
+        Detection and segmentation share ``YOLO_DEVICE`` and
+        ``YOLO_REQUIRE_CUDA``. Without this check segmentation could advertise
+        a GPU job while Ultralytics silently used CPU or failed only after the
+        model had already been loaded.
+        """
+
+        if not self.settings.yolo_require_cuda:
+            return
+        try:
+            import torch
+        except Exception as exc:
+            raise AppError(
+                code="SEGMENTATION_ACCELERATOR_UNAVAILABLE",
+                message="NVIDIA CUDA is required for configured segmentation, but PyTorch is not importable.",
+                status_code=503,
+            ) from exc
+        if not torch.cuda.is_available():
+            raise AppError(
+                code="SEGMENTATION_ACCELERATOR_UNAVAILABLE",
+                message="NVIDIA CUDA is required for configured segmentation, but no CUDA device is available.",
+                details={"configured_device": self.settings.yolo_device},
+                status_code=503,
+            )
+        if not str(self.settings.yolo_device).lower().startswith(("cuda", "0", "1", "2", "3")):
+            raise AppError(
+                code="SEGMENTATION_ACCELERATOR_MISCONFIGURED",
+                message="NVIDIA CUDA is required, but YOLO_DEVICE does not select a CUDA device.",
+                details={"configured_device": self.settings.yolo_device},
+                status_code=503,
+            )
 
     def _predict(self, model, tile_path: Path, confidence_threshold: float) -> list[Any]:
         if not tile_path.exists() or not tile_path.is_file():