bugfix: synchronize MTP compute stream after draft/validate forward.

[yingxudeng]

Description

Related Issues

Change Type

• Bug fix
• New feature
• Performance improvement
• Refactor
• Documentation
• Test
• Build or CI

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Reviewer Notes

[gemini-code-assist]

Code Review

This pull request modifies run_llm_no_sync_impl in mtp_worker_impl.cpp to synchronize the compute stream and assert on its return value. The review feedback points out that performing synchronization inside a function explicitly designed for asynchronous execution (no_sync) violates its contract and can hinder performance pipelining. Additionally, the return value of synchronize() should be declared as a plain int rather than int32_t to match the API signature, as per the repository style guide.

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[yingxudeng]

bugfix:
F20260627 17:21:22.615046 3253981 mtp_worker_impl.cpp:318] Check failed: state.token_id == token_id (539 vs. 19) MTP decode target state token mismatch, request_id=chatcmpl-2551906557222686169-xaLgCSacqP7RJtXV2rzbQv
*** Check failure stack trace: ***
@ 0x6f6310 google::LogMessage::SendToLog()
@ 0x6f2e0c google::LogMessage::Flush()
@ 0x6f68e0 google::LogMessageFatal::~LogMessageFatal()
@ 0xc770f0 xllm::MTPWorkerImpl::step_decode()
@ 0xcbd35c xllm::SpeculativeWorkerImpl::step()
@ 0xc02388 _ZZN4xllm10WorkerImpl10step_asyncERKNS_12ForwardInputEENUlvE_clEv
@ 0x31e3720 xllm::ThreadPool::internal_loop()
@ 0x31e4410 _ZNSt6thread11_State_implINS_8_InvokerISt5tupleIJZN4xllm10ThreadPoolC4EmN5folly8FunctionIFvvEEEbRKNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEEEUlvE_EEEEE6_M_runEv
@ 0xffff878c9da4 (unknown)
@ 0xffff7825fbb4 (unknown)
@ 0xffff782c7f4c (unknown)
@ (nil) (unknown)