fix(gateway): keep google's original finish reason

[steebchen]

Google requests were always logged with finish reason content_filter, hiding the reason Google actually returned.

Two causes:

• In parse-provider-response.ts, a response with no candidates set finishReason = "content_filter" before the promptFeedback.blockReason assignment, which is guarded by if (!finishReason). The real reason was therefore always discarded. It is now preserved. When Google reports no reason at all — no candidates, no blockReason, no candidate finish reason — the finish reason is left unset (logged as unknown) rather than guessing at a block; the existing warning still carries the full response body for diagnosis.
• NO_IMAGE, IMAGE_OTHER and OTHER were mapped to content_filter. NO_IMAGE means generation finished without emitting an image, and the other two are Google's unspecified / forward-compatibility buckets — none is a policy block. They now map to stop on the OpenAI surface and to unknown in the logs, alongside the existing OTHER handling.

This also removes a disagreement between map-finish-reason-to-openai.ts and logs.ts, which classified OTHER differently. Genuine blocks (SAFETY, PROHIBITED_CONTENT, IMAGE_SAFETY, IMAGE_PROHIBITED_CONTENT, BLOCKLIST, SPII, RECITATION, IMAGE_RECITATION, LANGUAGE) are unchanged.

NO_IMAGE and IMAGE_OTHER are added to isExpectedUnknownFinishReason so the new unknown mapping does not log an error on every occurrence.

🤖 Generated with Claude Code

[chatgpt-codex-connector]

You have reached your Codex usage limits for code reviews. You can see your limits in the Codex usage dashboard.

[Copilot]

Copilot was unable to review this pull request because the user who requested the review has reached their quota limit.

[coderabbitai]

Walkthrough

Google finish-reason parsing now preserves provider block reasons before fallback. Non-policy image reasons map to stop and log as UNKNOWN; policy reasons remain content_filter.

Changes

Google finish reason normalization

Layer / File(s)	Summary
Preserve Google block reasons apps/gateway/src/chat/tools/parse-provider-response.ts, apps/gateway/src/chat/tools/parse-provider-response.spec.ts	The parser preserves Google prompt and candidate block reasons before applying the content_filter fallback.
Map Google finish reasons apps/gateway/src/chat/tools/map-finish-reason-to-openai.ts	Non-policy image and unspecified Google reasons map to stop. Policy-related reasons remain content_filter.
Classify Google log results apps/gateway/src/lib/logs.ts, apps/gateway/src/lib/logs.spec.ts	Google IMAGE_OTHER, NO_IMAGE, OTHER, and MALFORMED_RESPONSE classify as UNKNOWN. Related expectations are updated.

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

Possibly related PRs

• theopenco/llmgateway#3254: Modifies shared finish-reason mapping and logging.
• theopenco/llmgateway#3492: Updates provider-specific finish-reason parsing and tests.

Suggested reviewers: bhuvan2134686

🚥 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 describes the main change: preserving Google’s original finish reason in the gateway.
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 gemini3-image-content-filter

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

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

[coderabbitai]

🧹 Nitpick comments (1)

apps/gateway/src/lib/logs.ts (1)

28-39: 📐 Maintainability & Code Quality | 🔵 Trivial | ⚡ Quick win

Add direct coverage for the new expected unknown reasons.

isExpectedUnknownFinishReason now suppresses logging for IMAGE_OTHER and NO_IMAGE. The supplied tests cover only OTHER and MALFORMED_RESPONSE. Add assertions for both new reasons so a later change does not re-enable erroneous unknown-reason logging.

🤖 Prompt for 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.

In `@apps/gateway/src/lib/logs.ts` around lines 28 - 39, Add direct test
assertions for IMAGE_OTHER and NO_IMAGE in the isExpectedUnknownFinishReason
test coverage, verifying both return the expected unknown-result behavior for
supported providers. Keep the existing OTHER and MALFORMED_RESPONSE assertions
unchanged.

🤖 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.

Nitpick comments:
In `@apps/gateway/src/lib/logs.ts`:
- Around line 28-39: Add direct test assertions for IMAGE_OTHER and NO_IMAGE in
the isExpectedUnknownFinishReason test coverage, verifying both return the
expected unknown-result behavior for supported providers. Keep the existing
OTHER and MALFORMED_RESPONSE assertions unchanged.

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 3934d21d-8bf4-463d-b9b8-98df96bbfb05

📥 Commits

Reviewing files that changed from the base of the PR and between c1cd97b and 0bcdb45.

📒 Files selected for processing (5)

• apps/gateway/src/chat/tools/map-finish-reason-to-openai.ts
• apps/gateway/src/chat/tools/parse-provider-response.spec.ts
• apps/gateway/src/chat/tools/parse-provider-response.ts
• apps/gateway/src/lib/logs.spec.ts
• apps/gateway/src/lib/logs.ts