fix(xai): map the provider finish reason instead of hardcoding stop

[JamMaster1999]

Description

Re-creation of #1304 by @tonycoder-hub, which was closed as stale on 2026-08-21 without a review. His commit is cherry-picked unchanged, Co-authored-by trailer intact, onto current main, where it applies cleanly.

From the original: the xAI converters hardcoded finish_reason. Non-streaming used tool_calls if tool_calls else stop, so REASON_MAX_LEN and REASON_MAX_CONTEXT came back as a clean stop and _acompletion_with_structured_output never raised LengthFinishReasonError. Streamed chunks hardcoded finish_reason=None, so a stream never said why it ended. sample_pb2.FinishReason is now mapped onto the OpenAI vocabulary in both converters, with truncation taking priority over tool_calls. Same shape as #1301 for Cohere, which merged.

Verified live on this branch with grok-4-1-fast-non-reasoning:

call	finish_reason
non-streaming, max_tokens=8	length (main hardcodes stop here)
non-streaming, normal	stop
streaming, max_tokens=8, last chunk	length (main hardcodes None here)

Tests: tests/unit/providers/test_xai_provider.py, 23 passed. Pre-commit clean.

PR Type

• 🐛 Bug Fix

Relevant issues

Supersedes #1304.

Checklist

• I understand the code I am submitting.
• I have added unit tests that prove my fix/feature works
• I have run this code locally and verified it fixes the issue.
• New and existing tests pass locally
• Documentation was updated where necessary (not applicable)
• I have read and followed the contribution guidelines
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  • This is fully AI-generated.

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• AI Model used: Claude (Opus 5) for the rebase, live verification and this description. The commit itself is @tonycoder-hub's, authored with Cursor.

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Summary by CodeRabbit

• Bug Fixes

  • Improved handling of xAI completion and streaming termination reasons.
  • Responses now correctly distinguish between stopped, length-limited, and tool-call outcomes.
  • Truncated tool-call responses are now reported as length-limited rather than completed tool calls.

• Tests

  • Added coverage for completion and streaming finish-reason mapping, including invalid and truncated responses.

[coderabbitai]

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ℹ️ Recent review info

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Configuration used: Organization UI

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Reviewing files that changed from the base of the PR and between c4f4bf1 and f7830c9.

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• tests/unit/providers/test_xai_provider.py

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Walkthrough

The xAI provider now maps finish reasons for streaming chunks and completed responses. Completed responses preserve truncation and termination reasons before applying tool-call or stop fallbacks. Unit tests cover these mappings and tool-call behaviour.

Changes

xAI finish reason handling

Layer / File(s)	Summary
Finish reason conversion src/any_llm/providers/xai/utils.py, tests/unit/providers/test_xai_provider.py	The provider maps xAI finish reasons to stop, length, and tool_calls. Streaming chunks now expose the mapped reason. Tests cover mapped and invalid reasons.
Completed response finish reasons src/any_llm/providers/xai/utils.py, tests/unit/providers/test_xai_provider.py	Completed responses prioritise recognised termination or truncation reasons. Tests verify that truncated tool calls return length and complete tool calls return tool_calls.

Suggested reviewers: njbrake

Merge Risk: ⚪ Minimal · up to f7830

The change correctly reports xAI termination reasons, including length limits, so downstream callers can distinguish truncated responses from normal completion. No actionable merge-blocking risk remains after normal checks and review.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 55.56% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 9 functions across 2 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main change: mapping xAI finish reasons instead of hardcoding the finish reason.
Description check	✅ Passed	The description is complete and follows the repository template. It explains the fix, identifies the bug-fix type, references the related issue, records verification and test results, completes the ch…
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.

Full details: Description check

Explanation

The description is complete and follows the repository template. It explains the fix, identifies the bug-fix type, references the related issue, records verification and test results, completes the checklist, and provides AI usage information.

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Actionable comments posted: 1

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Inline comments:
In `@tests/unit/providers/test_xai_provider.py`:
- Line 108: Update the test using mock_response.finish_reason to use
REASON_TIME_LIMIT, provide a non-empty tool_calls list, and assert that the
provider returns "tool_calls", ensuring the unmapped finish-reason fallback
branch is exercised.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Pro Plus

Run ID: 41a90e66-a201-43ed-8b23-45fb8659caa8

📥 Commits

Reviewing files that changed from the base of the PR and between e822b28 and c4f4bf1.

📒 Files selected for processing (2)

• src/any_llm/providers/xai/utils.py
• tests/unit/providers/test_xai_provider.py

Included review availability: Your plan provides up to 8 included reviews per hour; 6 remain after this review.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

Files with missing lines	Coverage Δ
src/any_llm/providers/xai/utils.py	58.66% <100.00%> (-9.91%)	⬇️

... and 31 files with indirect coverage changes

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