Google Gemini provider (Generative Language API / Vertex-compatible).
- Translate contract ⇄
generateContent (contents/parts, functionDeclarations, functionCall/functionResponse parts).
- Handle system_instruction, usageMetadata for tokens/cost; price table for Gemini models.
- Decide: API-key Generative Language API first (simple), Vertex auth later.
Google Gemini provider (Generative Language API / Vertex-compatible).
generateContent(contents/parts,functionDeclarations,functionCall/functionResponseparts).