fix(server): Inline think-tags when reasoning content present by tgasser-nv · Pull Request #2316 · NVIDIA-NeMo/Guardrails

tgasser-nv · 2026-08-20T15:45:40Z

Description

When IORails added support for GenerationOptions / GenerationResponse structured output in #2178, the reasoning_content response from the main LLM was returned in the corresponding GenerationResponse.reasoning_content field. Prior to this, reasoning_content fro the main LLM inference was prefixed using think-tags, for example:

<think>Reasoning here</think>Content here

QA test cases expect the think-tag inlined reasoning to be present from the nemoguardrails server application. In #2178 the GenerationResponse had reasoning_content in the correct field, but the server neither added it to the context using think-tags nor exposed it on the reasoning_content field of GenerationResponse.

To fix the issue and return correct reasoning_content in the dedicated field, see #2315 .

This PR point-fixes the IORails path by prefixing reasoning _content with think-tags in the regular content field

Related Issue(s)

JIRA NGUARD-881
NVBug 6469002

Verification

Pre-commit

$ uv run pre-commit run --all-files
check yaml...............................................................Passed
fix end of files.........................................................Passed
trim trailing whitespace.................................................Passed
ruff (legacy alias)......................................................Passed
ruff format..............................................................Passed
Insert license in comments...............................................Passed
zizmor...................................................................Passed
ty.......................................................................Passed

Unit-test

$ make test
env -u OPENAI_API_KEY -u NVIDIA_API_KEY -u LIVE_TEST -u LIVE_TEST_MODE -u TEST_LIVE_MODE uv run pytest -n auto --dist worksteal  
============================= test session starts ==============================
platform darwin -- Python 3.13.2, pytest-9.1.1, pluggy-1.6.0
rootdir: /Users/tgasser/projects/nemo_guardrails_worktree/fix/iorails-server-reasoning-thinktags
configfile: pytest.ini (WARNING: ignoring pytest config in pyproject.toml!)
testpaths: tests, benchmark/tests
plugins: langsmith-0.9.4, inline-snapshot-0.33.0, recording-0.13.4, cov-7.1.0, anyio-4.14.1, xdist-3.8.0, asyncio-1.4.0, httpx-0.36.2, profiling-1.8.1
asyncio: mode=Mode.STRICT, debug=False, asyncio_default_fixture_loop_scope=function, asyncio_default_test_loop_scope=function
created: 10/10 workers
10 workers [7259 items]

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══════════════════════════════════════════════════════════════════════ inline-snapshot ═══════════════════════════════════════════════════════════════════════
INFO: inline-snapshot was disabled because you used xdist. This means that tests with snapshots will continue to run, but snapshot(x) will only return x and 
inline-snapshot will not be able to fix snapshots or generate reports.


====================== 7048 passed, 211 skipped in 47.33s ======================

Integration tests

Direct-check with Main LLM

invoke_url='https://integrate.api.nvidia.com/v1/chat/completions'

payload=$(cat <<'JSON'
{
  "model": "nvidia/nemotron-3-nano-30b-a3b",
  "messages": [{"role":"user","content":"Hello!"}],
  "temperature": 1,
  "top_p": 0.95,
  "max_tokens": 16384,
  "reasoning_budget": 16384,
  "chat_template_kwargs": {"enable_thinking":true},
  "stream": false
}
JSON
)

curl -sS -N \
  --request POST \
  --url "$invoke_url" \
  --header "Authorization: Bearer $NVIDIA_API_KEY" \
  --header "Accept: application/json" \
  --header "Content-Type: application/json" \
  --data "$payload" | jq
{
  "id": "chatcmpl-4e8eb7e0-b6ce-42fb-a747-0b07e84b1be1",
  "choices": [
    {
      "index": 0,
      "message": {
        "content": "Hello! 😊 How can I assist you today? Feel free to ask me anything—I'm here to help!",
        "role": "assistant",
        "reasoning_content": "Okay, the user just said \"Hello!\" That's pretty straightforward. I should respond politely and warmly. Let me think about how to approach this.\n\nFirst, I need to acknowledge their greeting. Maybe say something like \"Hello!\" back to keep it friendly. Then, since they're starting a conversation, I should offer help to keep it open-ended. \n\nHmm, what's the best way to phrase it? \"Hello! How can I assist you today?\" That sounds good. It's welcoming and invites them to explain what they need help with. \n\nI should make sure my response is simple and not too formal. Keep it natural. Maybe add an emoji to keep it friendly? Like a smiley face. But I need to check if the platform allows emojis. Since the user didn't specify any restrictions, a simple 😊 should be fine.\n\nWait, the user might be testing if I'm responsive or just greeting me. So keeping it open is important. They might have a question or need help with something specific. \n\nAlso, considering the conversation history, this is the first message, so there's no context to refer back to. Just a simple, friendly reply. \n\nI think \"Hello! 😊 How can I assist you today?\" covers it. It's concise, friendly, and invites them to ask anything. That should work.\n"
      },
      "finish_reason": "stop",
      "logprobs": null
    }
  ],
  "created": 1787241523,
  "model": "nvidia/nemotron-3-nano-30b-a3b",
  "service_tier": null,
  "system_fingerprint": null,
  "object": "chat.completion",
  "usage": {
    "prompt_tokens": 18,
    "completion_tokens": 312,
    "total_tokens": 330
  }
}

Integration test with Server

Server

$ NEMO_GUARDRAILS_IORAILS_ENGINE=1 \
MAIN_MODEL_ENGINE=nim \
MAIN_MODEL_BASE_URL=https://integrate.api.nvidia.com/v1 \
 uv run nemoguardrails server --config ~/utils/configs --default-config-id content_safety

Client

$ curl -X POST http://localhost:8000/v1/chat/completions \
  -H "Content-Type: application/json" \
  -d '{
           "messages": [
            {
              "role": "user",
              "name": "text",
              "content": "Hello!"
            }
          ],
          "model": "nvidia/nemotron-3-nano-30b-a3b",
          "stream": false,
          "max_completion_tokens": 55

  }' | jq
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100   679  100   395  100   284    126     90  0:00:03  0:00:03 --:--:--   217
{
  "id": "chatcmpl-91715335-53ac-428c-aa19-bd1056966e6b",
  "choices": [
    {
      "finish_reason": "stop",
      "index": 0,
      "message": {
        "content": "<think>We need to respond. There's no special instruction. Just greeting.\n</think>\nHello! How can I help you today?",
        "role": "assistant"
      }
    }
  ],
  "created": 1787241625,
  "model": "nvidia/nemotron-3-nano-30b-a3b",
  "object": "chat.completion",
  "guardrails": {
    "config_id": "content_safety"
  }
}

AI Assistance

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Checklist

I've read the CONTRIBUTING guidelines.
This PR links to a triaged issue assigned to me.
My PR title follows the project commit convention.
I've updated the documentation if applicable.
I've added tests if applicable.
I've noted any verification beyond CI and any checks I couldn't run.
I did not update generated changelog files manually.
I addressed all CodeRabbit, Greptile, and other review comments, or replied with why no change is needed.
@mentions of the person or team responsible for reviewing proposed changes.

Summary by CodeRabbit

New Features
- Non-streaming responses from supported I/O integrations now include available reasoning in a leading <think>...</think> block.
- Reasoning content is preserved when responses contain non-text content or cannot be safely updated.
Bug Fixes
- Prevented duplicate <think> blocks when reasoning is already embedded.
- Improved consistency when converting between structured reasoning and inline think-tag content.
- Responses without reasoning remain unchanged.

codecov · 2026-08-20T15:53:18Z

Codecov Report

❌ Patch coverage is 90.00000% with 2 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
nemoguardrails/server/api.py	87.50%	2 Missing ⚠️

📢 Thoughts on this report? Let us know!

coderabbitai · 2026-08-20T16:12:17Z

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

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📥 Commits

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📒 Files selected for processing (2)

nemoguardrails/server/api.py
tests/server/test_iorails_engine_compat.py

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📝 Walkthrough

Walkthrough

Changes

Reasoning Inlining

Layer / File(s)	Summary
Think-tag formatting helper `nemoguardrails/llm/call.py`, `tests/llm/test_call_reasoning.py`	Adds `_prepend_think_tags` and tests for empty, missing, multiline, and round-trip reasoning content.
Guardrails response integration `nemoguardrails/server/api.py`	Inlines reasoning into eligible assistant messages only for non-streaming `Guardrails` responses backed by `IORails`. It clears `reasoning_content` only after insertion.
Reasoning preservation validation `tests/server/test_iorails_engine_compat.py`	Tests IORails folding, fallback `LLMRails` behavior, tool calls, missing assistant messages, bare responses, multi-message responses, and duplicate-tag prevention.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Merge Risk: ⚪ Minimal · up to 454ba

The PR restores think-tagged reasoning in server responses when reasoning content is present, matching the expected response format. No actionable merge-blocking risk remains based on the supplied evidence.

Suggested reviewers: pouyanpi, m-misiura

Sequence Diagram(s)

sequenceDiagram
  participant Client
  participant Guardrails
  participant IORails
  participant ResponseAdapter
  participant AssistantMessage
  Client->>Guardrails: submit non-streaming request
  Guardrails->>IORails: process request
  IORails-->>Guardrails: return assistant content and reasoning_content
  Guardrails->>ResponseAdapter: fold eligible reasoning
  ResponseAdapter->>AssistantMessage: prepend reasoning as <think> tags
  ResponseAdapter-->>Client: return updated response

🚥 Pre-merge checks | ✅ 6

✅ Passed checks (6 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main server change: inlining reasoning content with think-tags.
Docstring Coverage	✅ Passed	Docstring coverage is 80.00% which is sufficient. The required threshold is 80.00%.
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.
Test Results For Major Changes	✅ Passed	The PR changes server reasoning formatting and adds focused tests. The description documents pre-commit, 7,048 passed/211 skipped unit tests, and direct/server integration results.

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Commit unit tests in branch fix/iorails-server-reasoning-thinktags

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Actionable comments posted: 1

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Inline comments:
In `@nemoguardrails/server/api.py`:
- Around line 808-810: Restrict the _inline_reasoning_as_think_tags call in the
Guardrails/GenerationResponse branch to cases where llm_rails.rails_engine is an
IORails instance. Update the contrast test to wrap an LLMRails-backed Guardrails
instance instead of relying on _StubLLMRails, while preserving existing request
and response shapes.

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📒 Files selected for processing (4)

nemoguardrails/llm/call.py
nemoguardrails/server/api.py
tests/llm/test_call_reasoning.py
tests/server/test_iorails_engine_compat.py

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greptile-apps · 2026-08-20T16:12:54Z

Greptile Summary

This PR restores reasoning in non-streaming IORails server responses by placing structured reasoning into a leading <think>...</think> block.

Adds a shared helper for prepending think tags.
Applies the conversion only when the Guardrails wrapper is backed by IORails.
Adds unit and server compatibility coverage for structured reasoning, tool calls, engine fallback, and existing inline blocks.

Confidence Score: 4/5

The PR is not yet safe to merge because a non-leading complete think block in assistant content still causes structured provider reasoning to disappear from the HTTP response.

The earlier incidental-think-tag issue remains reachable: the current unanchored regex matches a complete block anywhere in content, skips inlining, and leaves reasoning in a field that the response converter does not serialize.

Files Needing Attention: nemoguardrails/server/api.py

Important Files Changed

Filename	Overview
nemoguardrails/llm/call.py	Adds a focused helper that prefixes non-empty structured reasoning as a think block.
nemoguardrails/server/api.py	Adds IORails-specific reasoning inlining, but the unanchored existing-block matcher still drops structured reasoning for non-leading complete think blocks.
tests/llm/test_call_reasoning.py	Covers helper behavior and round-trip compatibility with think-tag extraction.
tests/server/test_iorails_engine_compat.py	Adds extensive IORails server coverage, but the mid-content case does not include a complete closing think tag and therefore misses the outstanding regression.

_{Reviews (5): Last reviewed commit: "Use regex to detect thinking tags" | Re-trigger Greptile}

tgasser-nv · 2026-08-20T18:39:21Z

@coderabbitai review

coderabbitai · 2026-08-20T18:39:27Z

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Pouyanpi

Looks good to merge 👍🏻

Prepend think-tags for IORails only

b115b47

github-actions Bot added size: M status: needs triage New issues that have not yet been reviewed or categorized. labels Aug 20, 2026

tgasser-nv self-assigned this Aug 20, 2026

tgasser-nv added status: triaged Triaged by a maintainer; eligible for automated review (CodeRabbit/Greptile). and removed status: needs triage New issues that have not yet been reviewed or categorized. labels Aug 20, 2026

tgasser-nv marked this pull request as ready for review August 20, 2026 16:09

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Address review feedback

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Use regex to detect thinking tags

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Pouyanpi self-requested a review August 20, 2026 19:48

Pouyanpi approved these changes Aug 20, 2026

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tgasser-nv merged commit d49ff41 into develop Aug 20, 2026
27 checks passed

tgasser-nv deleted the fix/iorails-server-reasoning-thinktags branch August 20, 2026 20:10

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fix(server): Inline think-tags when reasoning content present - #2316

fix(server): Inline think-tags when reasoning content present#2316
tgasser-nv merged 4 commits into
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fix/iorails-server-reasoning-thinktags

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Description

Related Issue(s)

Verification

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Unit-test

Integration tests

Direct-check with Main LLM

Integration test with Server

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Important Files Changed

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