env_setup/backbone_sanity_check.py

import torch
import torchvision.models as models

backbone = models.resnet18(pretrained=True)
backbone.fc = torch.nn.Identity()   # strip final FC → 512-d output
backbone.eval()

dummy = torch.randn(1, 3, 224, 224)
with torch.no_grad():
    emb = backbone(dummy)

print(f"Embedding shape : {emb.shape}")   # expect torch.Size([1, 512])