feat: Add dedicated merged mode to Megatron backend

src/art/megatron/job_protocol.py

@@ -0,0 +1,68 @@
+from typing import Annotated, Literal, TypeAlias
+
+from pydantic import BaseModel, Field, TypeAdapter
+
+from art import dev, types
+from art.megatron.routing_replay import MoeRoutingReplayBundle
+from art.preprocessing.pack import DiskPackedTensors
+
+
+class MergedWeightTransferInitInfo(BaseModel):
+    master_address: str
+    master_port: int
+    rank_offset: int
+    world_size: int
+
+
+class MergedWeightTransferSpec(BaseModel):
+    init_info: MergedWeightTransferInitInfo
+    vllm_base_url: str
+    served_model_name: str
+
+
+class MegatronSyncJob(BaseModel):
+    kind: Literal["sync"]
+    lora_path: str
+    merged_weight_transfer: MergedWeightTransferSpec
+
+
+class _MegatronTrainJobBase(BaseModel):
+    lora_path: str
+    optimizer_state_path: str
+    disk_packed_tensors: DiskPackedTensors
+    config: types.TrainConfig
+    experimental_config: dev.TrainConfig
+    moe_routing_replay_path: str | None = None
+    moe_routing_replay_strict: bool = True
+
+
+class MegatronLoraTrainJob(_MegatronTrainJobBase):
+    kind: Literal["train_lora"]
+
+
+class MegatronMergedTrainJob(_MegatronTrainJobBase):
+    kind: Literal["train_merged"]
+    merged_weight_transfer: MergedWeightTransferSpec
+
+
+MegatronLoraTrainJob.model_rebuild(
+    force=True,
+    _types_namespace={"MoeRoutingReplayBundle": MoeRoutingReplayBundle},
+)
+MegatronMergedTrainJob.model_rebuild(
+    force=True,
+    _types_namespace={"MoeRoutingReplayBundle": MoeRoutingReplayBundle},
+)
+
+MegatronJob: TypeAlias = Annotated[
+    MegatronSyncJob | MegatronLoraTrainJob | MegatronMergedTrainJob,
+    Field(discriminator="kind"),
+]
+
+
+def dump_megatron_job(job: MegatronJob) -> str:
+    return TypeAdapter(MegatronJob).dump_json(job).decode()
+
+
+def load_megatron_job(raw: str | bytes) -> MegatronJob:
+    return TypeAdapter(MegatronJob).validate_json(raw)

src/art/megatron/provider.py

@@ -80,6 +80,7 @@ def get_provider(
             )
         )
     provider = bridge.to_megatron_provider()
+    setattr(provider, "art_bridge", bridge)
     base_layer_spec = provider.transformer_layer_spec
 
     def _flex_attention_layer_spec(