- Added tests (`TestCliFinishReasonOnlyOnFinalChunk`, `TestGeminiFinishReasonOnlyOnFinalChunk`) to validate correct `finish_reason` and `native_finish_reason` assignment.
- Refactored Gemini and CLI translators to track `SawToolCall` and `UpstreamFinishReason` for accurate final-chunk determination.
- Improved response parsing logic to align with upstream metadata and provide consistent reasoning on chunk outputs.