fix(server): handle stop and malformed messages

[Pouyanpi]

Summary

Fixes NGUARD-880 stop handling, streaming normalization, and malformed-message validation.

AI Assistance

• AI tools were used; a human reviewed and can explain every change (tool: Codex).

Stack Position

Part 2 of 2.

• Previous: test(llm): move call tests to module mirrors #2265
• Next: none, final stack PR

Stack Context

Moves llm_call tests first so the NGUARD-880 fix is reviewed as a small behavioral diff.

Please review each PR against its parent branch, not directly against the root base branch, except for part 1.

Order	PR	Branch	Base
1	#2265	pouyanpi/refactor-llm-call-tests	develop
2	#2266	pouyanpi/fix-nguard-880-stop-and-messages	pouyanpi/refactor-llm-call-tests

Validation

89 passed, 3 skipped
pre-commit passed

[greptile-apps]

Greptile Summary

The PR fixes propagation of OpenAI-compatible stop parameters and adds early validation for chat messages missing a role.

• Copies LLM parameters before extracting stop, avoiding duplicate keyword arguments and caller-owned dictionary mutation.
• Normalizes string stop values for streaming-handler matching.
• Rejects role-less chat messages with an OpenAI-shaped validation response.
• Adds streaming, non-streaming, API propagation, and malformed-message regression tests.

Confidence Score: 5/5

The PR appears safe to merge with no actionable regressions identified.

The stop-parameter path now avoids duplicate arguments without mutating caller input, while malformed messages lacking roles are rejected before rails initialization.

Important Files Changed

Filename	Overview
nemoguardrails/llm/call.py	Safely extracts stop parameters from a copied options dictionary and normalizes streaming-handler stop state.
nemoguardrails/server/schemas/openai.py	Adds permissive message-object validation that requires a string role while preserving extra OpenAI-compatible fields.
tests/llm/test_call.py	Covers stop precedence, input immutability, and streaming normalization across string, list, and null values.
tests/server/test_api.py	Covers malformed-message rejection and propagation of supported stop values into generation options.

_{Reviews (1): Last reviewed commit: "fix(streaming): normalize string stop se..." | Re-trigger Greptile}