fix: download yolo11m.pt via huggingface_hub to writable /tmp path

ultralytics YOLO() tries to download to CWD which is read-only in
the container. Use hf_hub_download to fetch weights to /tmp/yolo_weights
then load from that path.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

models/detectors/yolov11.py

@@ -1,19 +1,21 @@
 import logging
 import os
+from pathlib import Path
 from typing import List, Sequence
 
 import numpy as np
 import torch
-
-# Ensure ultralytics downloads weights to a writable directory (container /app is read-only)
-if "YOLO_CONFIG_DIR" not in os.environ:
-    os.environ["YOLO_CONFIG_DIR"] = "/tmp/ultralytics"
-
+from huggingface_hub import hf_hub_download
 from ultralytics import YOLO
 
 from models.detectors.base import DetectionResult, ObjectDetector
 from utils.tiling import get_slice_bboxes, slice_image, shift_bboxes, batched_nms
 
+# Download YOLO11m weights to a writable cache (container /app is read-only).
+_WEIGHTS_CACHE = Path(os.environ.get("YOLO_CACHE", "/tmp/yolo_weights"))
+_WEIGHTS_CACHE.mkdir(parents=True, exist_ok=True)
+_YOLO11M_PATH = _WEIGHTS_CACHE / "yolo11m.pt"
+
 
 class Yolo11Detector(ObjectDetector):
     """YOLO11m detector with COCO-pretrained weights from Ultralytics."""
@@ -37,7 +39,15 @@ class Yolo11Detector(ObjectDetector):
             "Loading YOLO11m COCO-pretrained weights onto %s",
             self.device,
         )
-        self.model = YOLO("yolo11m.pt")
+        # Download weights via huggingface_hub to a writable path, then load.
+        if not _YOLO11M_PATH.exists():
+            logging.info("Downloading yolo11m.pt to %s ...", _YOLO11M_PATH)
+            hf_hub_download(
+                repo_id="Ultralytics/YOLO11",
+                filename="yolo11m.pt",
+                local_dir=str(_WEIGHTS_CACHE),
+            )
+        self.model = YOLO(str(_YOLO11M_PATH))
         self.model.to(self.device)
         self.class_names = self.model.names