feat(zettasets): Fall back to zettasets images

[nkemnitz]

No description provided.

[torms3]

Control flow via exception (Claude Code)

Using raise ValueError just to catch it a few lines later is a code smell:

if sample.src_image_path is None:
    raise ValueError("No src_image_path available")
# ...
except (InfoUnavailableError, ValueError) as e:

This also has the side effect of catching genuine ValueErrors from CloudVolume internals. Consider restructuring to avoid exceptions as control flow:

vol = None
if sample.src_image_path is not None:
    try:
        vol = CloudVolume(
            sample.src_image_path,
            mip=resolution,
            fill_missing=True,
            bounded=False,
        )[image_bbox.to_slices()]
    except InfoUnavailableError as e:
        logging.warning(f"src_image_path failed ({e}), falling back to sample image volume")

if vol is None:
    vol = CloudVolume(
        sample.volumes["image"].cloudpath,
        mip=resolution,
        fill_missing=True,
        bounded=False,
    )[image_bbox.to_slices()]

This makes the None check and the InfoUnavailableError handling separate concerns, and avoids accidentally swallowing unrelated ValueErrors.

Unguarded fallback (@torms3)

The fallback assumes sample.volumes["image"] always exists. If it doesn't, the user gets an unhandled KeyError with no context. Consider validating before accessing:

if "image" not in sample.volumes:
    raise RuntimeError(
        f"src_image_path failed ({e}) and sample has no 'image' volume to fall back to"
    ) from e

This applies to both multi_zettaset.py and zettaset.py.