fix(guardrails): Surface 500 when guardrail result cannot be parsed

[JashG]

Summary

Addresses edge case where a rail result cannot be parsed from the underlying GenerationResponse. Previously, we blocked the request and DEBUG logged the error. This PR updates the plugin to return an explicit 500 with a WARNING log.

Changes

• responses.py: Refactored is_blocked_generation_response to accept GenerationLog directly instead of GenerationResponse. The caller (i.e. the plugin middleware) returns early if there is no GenerationLog.
• middleware.py: Added a log is None guard in both process_request (input rails) and process_response (output rails) that raises InferenceMiddlewareError(status_code=500) and logs at WARNING before the blocked/unblocked branch is evaluated.
• Updated tests

Type of Change

• Code change (feature, bug fix, or refactor)
• Code change with documentation updates
• Documentation only
• Contributor tooling or automation
• CI, build, or test infrastructure

Quality Gates

• Tests added or updated for changed behavior
• Existing tests cover changed behavior — justification:
• Tests not applicable — justification:
• Documentation updated for user-visible behavior
• Documentation not applicable — justification:

Verification

• Pull request title follows the repository's Conventional Commit format
• Every commit includes an appropriate Signed-off-by: trailer
• uv run pre-commit run -a passes, or any blocked checks are identified below
• Targeted tests pass, or tests are marked not applicable above
• No secrets, API keys, or credentials are included

Targeted validation:

uv run --frozen pytest plugins/nemo-guardrails/ -x -q
412 passed, 292 warnings

Summary by CodeRabbit

• Bug Fixes

  • Improved handling of missing generation logs during input and output guardrail processing.
  • Requests now return a clear HTTP 500 error when guardrail results cannot be determined.
  • Blocked responses are detected more reliably based on activated rail results.

• Tests

  • Added coverage for missing logs and blocked, allowed, empty, and non-stopping rail outcomes.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Enterprise

Run ID: 77e151a1-24ec-405c-af0d-e0bf51e965b3

📥 Commits

Reviewing files that changed from the base of the PR and between 378ca94 and 46ba18e.

📒 Files selected for processing (4)

• plugins/nemo-guardrails/src/nemo_guardrails_plugin/middleware.py
• plugins/nemo-guardrails/src/nemo_guardrails_plugin/responses.py
• plugins/nemo-guardrails/tests/unit/test_middleware.py
• plugins/nemo-guardrails/tests/unit/test_responses.py

---

📝 Walkthrough

Walkthrough

Guardrail middleware now rejects generation responses without activation logs with HTTP 500 errors. Block detection accepts GenerationLog directly and checks activated rails. Unit tests cover input, output, and blocked-generation cases.

Changes

Guardrail log handling

Layer / File(s)	Summary
Blocked response detection plugins/nemo-guardrails/src/nemo_guardrails_plugin/responses.py, plugins/nemo-guardrails/tests/unit/test_responses.py	is_blocked_generation_response now accepts GenerationLog and checks stopped activated rails. Tests cover stopped, non-stopped, empty, and explicitly non-blocking rails.
Middleware log validation plugins/nemo-guardrails/src/nemo_guardrails_plugin/middleware.py, plugins/nemo-guardrails/tests/unit/test_middleware.py	Input and output rail processing return a 500 InferenceMiddlewareError when GenerationResponse.log is missing. Tests validate both paths.

Suggested reviewers: a2bondar

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarizes the main change: returning HTTP 500 when the guardrail result cannot be parsed.
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.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/guardrails-missing-activation-log

---

_{Comment @coderabbitai help to get the list of available commands.}

[github-actions]

Suite	Lines Covered	Line Rate	Branch Rate
Unit Tests	32003/40616	78.8%	63.6%
Integration Tests	18553/38542	48.1%	20.8%