refactor: drop the full output from the greedy prefix verify kernel.

[wai-bao]

Summary

Drop the full target output from the greedy prefix verify kernel. The masked
output is now the only output, and the mask_out_rejected_tokens flag is
removed along with the whole mask=false path.

• greedy_prefix_verify returns a single torch::Tensor instead of a
  (full, masked) tuple; the kernel signature drops full_handle and the
  runtime mask_enabled branch.
• The host wrapper pre-fills the output with -1, so the kernel only writes
  tiles before each row's first rejection and can T.loop_break past it.
• RejectionSampler::forward no longer takes mask_out_rejected_tokens;
  finalize_random_sample and the tuple plumbing are removed.
• Consumers read the sentinel as < 0 instead of == -1: rejection sampler,
  worker model codecs (llm/rec/vlm), mtp_json_object_state,
  forward_shared_memory_manager, and unified_block_acl_graph.
• forward_shared_memory_manager gains a shared num_accepted_tokens helper
  used by both the sizing and write loops, replacing the placeholder-count
  writeback (row_count_cursor / serialized_tokens / trailing memcpy).
• The logprobs path gathers with clamp_min(0) and zeroes rejected entries
  with masked_fill_ so -1 sentinels never index the gather.

Summary by CodeRabbit

• Bug Fixes
  • Speculative decoding now treats any negative token ID as rejected or padding, rather than recognizing only -1.
  • Sampling results mask rejected tokens, and output sequences stop at the first negative token.
  • Accepted-token counts and sequence updates consistently follow the nonnegative-token rule across supported output types and execution paths.

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-17T21:27:20.896683Z	bbfe56e	New commits

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• Run ID: 3a5c3c84-d9a6-4eda-8417-01c82ca2ee7d

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📒 Files selected for processing: 1

• tests/core/framework/speculative/mtp_json_object_state_test.cpp

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📝 Walkthrough

Rejection sampling and greedy prefix verification now return masked token sequences without a masking option. Runtime acceptance checks, speculative payload serialization, JSON mismatch scanning, and output codecs now treat any negative token ID as a stopping sentinel.

Changes: Speculative Token Processing

Layer / File(s)	Summary
Greedy prefix verification API and kernel xllm/core/kernels/npu/tilelang/tilelang_ops_api.h, xllm/core/kernels/npu/tilelang/greedy_prefix_verify_wrapper.cpp, xllm/python/kernels_npu/tilelang/greedy_prefix_verify.py, tests/core/kernels/npu/tilelang/greedy_prefix_verify_wrapper_test.cpp	The API and kernel now return one int32 output with rejected-token masking. The tests validate the output definition, metadata, and input handling.
Rejection sampler outputs and call sites xllm/core/framework/sampling/rejection_sampler.*, xllm/core/framework/speculative/spec_verify.cpp, tests/core/framework/batch/batch_test.cpp, tests/core/framework/sampling/rejection_sampler_test.cpp, tests/core/framework/speculative/spec_metrics_test.cpp	The sampler drops the masking flag and returns masked tokens. Log probabilities use those output tokens. Call sites and tests use the updated API.
Negative sentinel handling across runtime paths xllm/core/runtime/forward_shared_memory_manager.cpp, xllm/core/runtime/task_execution_pipeline_speculative.cpp, xllm/core/framework/speculative/mtp_json_object_state.h, xllm/core/distributed_runtime/worker_model_codec_*.cpp, xllm/python/model_executor/runners/unified_block_acl_graph.py, tests/core/framework/speculative/mtp_json_object_state_test.cpp	Acceptance checks, JSON mismatch scanning, payload sizing and serialization, and output encoding now stop at any negative token ID.

Priority: ➖ Normal

Estimated code review effort: 3 (Moderate) | ~25 minutes

Change: Refactor

Merge Risk: ⚪ Minimal · up to bbfe5

Rejected-token masking and downstream handling are consistent in the inspected paths, with no actionable merge-blocking risk identified.

Pre-merge checks: 3 · 2

Failed checks: 2 warnings

Check name	Status	Explanation	Resolution
Description check		The description provides a relevant and detailed summary of the implementation changes, but it omits most required template sections, including Related Issues, Change Type, the Pull Request Checklist,…	Add the required template sections. State related issues or that none apply, select the applicable change type, complete the PR checklist, report pre-commit and CUDA/NPU/MLU test results or explain which checks were not run, document self-r…
Docstring Coverage		Docstring coverage is 12.96% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 54 functions across 18 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

Passed checks: 3 passed

Check name	Status	Explanation
Title check		The title accurately and concisely describes the primary change: removing the full output from the greedy prefix verify kernel. It uses the required refactor prefix, starts with a verb, contains suffi…
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

Full details: Title check

Explanation

The title accurately and concisely describes the primary change: removing the full output from the greedy prefix verify kernel. It uses the required refactor prefix, starts with a verb, contains sufficient detail, and ends with a period.

Full details: Description check

Explanation

The description provides a relevant and detailed summary of the implementation changes, but it omits most required template sections, including Related Issues, Change Type, the Pull Request Checklist, and Reviewer Notes. It also does not report validation results.

Resolution

Add the required template sections. State related issues or that none apply, select the applicable change type, complete the PR checklist, report pre-commit and CUDA/NPU/MLU test results or explain which checks were not run, document self-review and rebasing, and add reviewer notes or state that none apply.

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Actionable comments posted: 1

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• 🪄 Fix comments: Fix CodeRabbit comments on this PR

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Inline comments:
Review comments at @tests/core/framework/sampling/rejection_sampler_test.cpp:
- Around line 333-336: Update the expected-logprob calculation using
selected_tokens in the rejection sampler test to clamp negative sentinel IDs to
zero before passing them to gather, then keep masked_fill_ to zero out sentinel
positions.

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ℹ️ Review info

⚙️ Run configuration

• Configuration used: defaults
• Review profile: CHILL
• Plan: Advanced
• Run ID: 8f2fb173-5939-410c-a725-000d6ae0c5cb

📥 Commits

Reviewing files that changed from the base of the PR and between 9cb0072 and 5b3e800.

📒 Files selected for processing: 17

• tests/core/framework/batch/batch_test.cpp
• tests/core/framework/sampling/rejection_sampler_test.cpp
• tests/core/framework/speculative/spec_metrics_test.cpp
• tests/core/kernels/npu/tilelang/greedy_prefix_verify_wrapper_test.cpp
• xllm/core/distributed_runtime/worker_model_codec_llm.cpp
• xllm/core/distributed_runtime/worker_model_codec_rec.cpp
• xllm/core/distributed_runtime/worker_model_codec_vlm.cpp
• xllm/core/framework/sampling/rejection_sampler.cpp
• xllm/core/framework/sampling/rejection_sampler.h
• xllm/core/framework/speculative/mtp_json_object_state.h
• xllm/core/framework/speculative/spec_verify.cpp
• xllm/core/kernels/npu/tilelang/greedy_prefix_verify_wrapper.cpp
• xllm/core/kernels/npu/tilelang/tilelang_ops_api.h
• xllm/core/runtime/forward_shared_memory_manager.cpp
• xllm/core/runtime/task_execution_pipeline_speculative.cpp
• xllm/python/kernels_npu/tilelang/greedy_prefix_verify.py
• xllm/python/model_executor/runners/unified_block_acl_graph.py

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