- Include V2 width/height/num_frames and the train manifest in the step-0
fingerprint so a dimension change cannot reuse a stale baseline.
- Honor CompressionSpec.first_steps in the V2 rung scope.
- Mark tagged checkpoints weights-only in metadata and teach the exporter
to resolve and load them, so best/ can be exported.
- Add a tile-64 backward comparison against the STE reference.