fix: pad dummy run query_start_loc

[UranusSeven]

Hi from novita.ai team 👋

Purpose

The decoder instance crashes when running GLM-5.1-FP8 in disaggregation way. Cuda coredump shows:

/pytorch/aten/src/ATen/native/cuda/Repeat.cu:33: compute_cuda_kernel: block: [0,0,0], thread: [49,0,0] Assertion `repeat >= 0` failed.
/pytorch/aten/src/ATen/native/cuda/Repeat.cu:33: compute_cuda_kernel: block: [0,0,0], thread: [50,0,0/pytorch/aten/src/ATen/native/cuda/Repeat.cu] Assertion `repeat >= 0` failed.

By adding log before every torch.repeat_interleave call, I got:

WARNING 06-04 08:36:48 [logger.py:276] repeat_interleave[mla.indexer.expanded_offsets]: repeats={'shape': (2,), 'dtype': 'torch.int32', 'device': 'cuda:2', 'numel': 2, 'min': 0, 'max': 3, 'head': [3, 0]} negatives=[] input={'shape': (2,), 'dtype': 'torch.int32', 'device': 'cuda:2', 'numel': 2, 'min': -3, 'max': 14622, 'head': [14622, -3]} output_size=3 dim=None extra={'seq_lens': [14625, 0], 'decode_lens': [3, 0], 'decode_lens_cpu': [3, 0], 'query_start_loc': [0, 3], 'num_decodes': 2, 'num_decode_tokens': 6, 'max_decode_len': 3, 'min_decode_len': 0}
/pytorch/aten/src/ATen/native/cuda/Repeat.cu:33: compute_cuda_kernel: block: [0,0,0], thread: [32,0,0] Assertion `repeat >= 0` failed.
/pytorch/aten/src/ATen/native/cuda/Repeat.cu:33: compute_cuda_kernel: block: [0,0,0], thread: [33,0,0] Assertion `repeat >= 0` failed.

The root cause it that with dummy run, query_start_loc is not a monotonic sequence.

Test Plan

Run same requests with the fixed decoder.

Test Result

The decoder worked fine for several hours.

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[claude]

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[WoosukKwon]

LGTM. Thanks for the fix!