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Haoming Song
ef88d4e52b
* feat(train): parallel training engine with FSDP2, HSDP, and DCP checkpoints Replace the FSDP1 training path with a config-owned parallel-training engine: - Topology and runtime configs (--parallelism.*, --accelerator.*): dp_replicate x dp_shard degrees select single-process, DDP (unchanged default), FSDP2, or HSDP; mixed precision, first-class gradient accumulation, and FSDP/DDP tuning knobs are mirrored as plain dataclasses that build the accelerate objects at runtime, so every run is reproducible from its train_config.json alone. Accelerate env vars are guarded against configuring the engine behind the config system's back. - Declarative policy surface: policies declare FSDP2 wrap units (_fsdp_wrap_modules) and non-forward entry points (_fsdp_forward_methods); a shared engine resolves them around accelerator.prepare(). Context-parallel fields are reserved and validated to 1. - Checkpoints: selectable --checkpoint_format (safetensors | dcp | safetensors_dcp); the sharded optimizer channel is always DCP; two-phase resume (step+RNG before prepare, DCP model/optimizer after) reshards across GPU-topology changes; lerobot-convert-dcp merges DCP shards into a distributable model.safetensors offline. - Publishing: PreTrainedPolicy.push_model_to_hub is replaced by the free publish_trained_model (model + processors + card + train config, all-ranks gather with main-rank writes); PreTrainedPolicy._save_pretrained gathers state dicts internally, removing the state_dict= threading from save_pretrained. - lerobot_train is restructured around the engine: optimizer built before the single prepare() call, deferred weight load on DCP resumes, collective save_checkpoint with no call-site rank branches, dp-world-size-based sample accounting. Breaking changes: FSDP checkpoints from lerobot <= 0.6.x are not resumable (weights stay loadable via from_pretrained; pin lerobot==0.6.x to finish old runs); the `accelerate launch --config_file` yaml flow is superseded by the config flags; training autocast is owned exclusively by --accelerator.mixed_precision (policy.dtype only casts parameters). Also fixes: reward-model hub publishing crash (TypeError on extra kwargs). Verified by ~200 new CPU tests (config round-trips, checkpoint round-trips per format, two-phase resume, publisher contracts, converter equivalence, accelerate canaries), a 5-test 4-GPU suite (FSDP2 save/resume bit-exactness, HSDP/DDP loss parity, changed-topology resume, all-ranks save_pretrained, grad-accum equivalence), and end-to-end ACT (1/4/8 GPUs) + FastWAM 6B (FSDP2 + HSDP) training runs.