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Root Cause
Under sequence parallelism, entropy statistics and GRPO batch loss calibration were computed from sharded tensors, which could produce incorrect token counts and inconsistent metrics across SP ranks. In addition, GRPO loss batching needed to accept the forwarded SP context from the worker.
Fix
Gather shifted labels and logprobs before entropy aggregation under SP, pass sp_mesh into RL loss batching from the training worker, and make GRPO batch construction use the SP-aware token counting path.