scripts/checkpoint_conversion/cosmos3_convert.py wraps Cosmos3OmniDiffusersPipeline._remap_ckpt_key. convert_state_dict(src) returns (new_state, skipped, unmapped) for shard-by-shard remap; convert_checkpoint_dir reads *.safetensors shards and writes a consolidated FastVideo-format state dict (sharded index.json TODO when real weights land). smoke_test() exercises all 14 representative remap branches synthetically (no real weights needed) and returns nonzero exit on failure; runs in CI as a remap-drift guard. Usage: python scripts/checkpoint_conversion/cosmos3_convert.py --smoke-test.