[TRTLLM-14155][fix] Revert host-side greedy stop checks from #15920

[mingyangHao]

This reverts commit 4f1c3cd.

Summary by CodeRabbit

• Bug Fixes
  • Improved sampling behavior consistency across requests, especially for beam and greedy paths.
  • Finish-reason handling is now applied more reliably during token generation, reducing edge-case differences.
  • Removed a special-case path that could lead to inconsistent stopping behavior in some scenarios.

Description

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[coderabbitai]

📝 Walkthrough

Walkthrough

This change removes the host stop-criteria fast path from TorchSampler. SampleStateTorch replaces its use_host_stop_criteria field with beam_history_builders. _process_requests and sample_async now always compute and propagate seq_lens_host/seq_lens_cuda, and device-side finish-reason handling always runs. Associated unit tests for the removed fast path are deleted.

Changes

Host stop-criteria fast-path removal

Layer / File(s)	Summary
Dataclass and helper changes tensorrt_llm/_torch/pyexecutor/sampler/sampler.py	SampleStateTorch replaces use_host_stop_criteria with beam_history_builders; the _can_use_host_stop_criteria helper is removed.
update_requests always uses process_draft_tokens tensorrt_llm/_torch/pyexecutor/sampler/sampler.py	Single-beam branch always calls process_draft_tokens(...) instead of conditionally short-circuiting on host stop criteria.
_process_requests unconditional seq_lens computation tensorrt_llm/_torch/pyexecutor/sampler/sampler.py	_process_requests always computes and returns seq_lens_host/seq_lens_cuda, simplifies destination indexing in the fast greedy path, and updates return tuple ordering for both fast and non-fast paths.
sample_async unpacking and finish-reason handling tensorrt_llm/_torch/pyexecutor/sampler/sampler.py	sample_async updates unpacking of returned values, always runs device-side finish-reason handling, and SampleStateTorch construction reflects the new field.
Remove host stop-criteria fast-path tests tests/unittest/_torch/sampler/test_torch_sampler.py	Deletes tests validating the fast path and its fallback behavior.

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

Suggested reviewers: ziyixiong-nv, dongxuy04, hnover-nv

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	The description only states it reverts a commit and omits the required issue/solution and test coverage sections.	Add a short Description explaining what changed and why, list relevant Test Coverage, and ensure the PR Checklist is complete.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title is concise and accurately summarizes the main change as reverting host-side greedy stop checks.

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@tensorrt_llm/_torch/pyexecutor/sampler/sampler.py`:
- Line 3787: The `sample_async` unpacking includes `seq_lens_host`, but that
symbol is never used afterward and triggers RUF059. Update the unpacking near
`sample_async` so only the needed values are assigned, or replace the unused
slot with a throwaway placeholder, while keeping the existing `seq_lens_cuda`
flow into `write_finish_reasons` and `_update_original_tokens` intact.

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Fix all unresolved CodeRabbit comments on this PR:

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📥 Commits

Reviewing files that changed from the base of the PR and between 60583d2 and cc19fe7.

📒 Files selected for processing (2)

• tensorrt_llm/_torch/pyexecutor/sampler/sampler.py
• tests/unittest/_torch/sampler/test_torch_sampler.py

💤 Files with no reviewable changes (1)

• tests/unittest/_torch/sampler/test_torch_sampler.py

[mingyangHao]

/bot run --add-multi-gpu-test --disable-fail-fast

[tensorrt-cicd]

PR_Github #58364 [ run ] triggered by Bot. Commit: 8efd819 Link to invocation

[chzblych]

/bot skip --comment "Bring TOT main back to normal"

[tensorrt-cicd]

PR_Github #58390 [ skip ] triggered by Bot. Commit: 6fcfd81 Link to invocation

[tensorrt-cicd]

PR_Github #58364 [ run ] completed with state ABORTED. Commit: 8efd819

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[tensorrt-cicd]

PR_Github #58390 [ skip ] completed with state SUCCESS. Commit: 6fcfd81
Skipping testing for commit 6fcfd81

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