Support Vertex AI batch behavior for inline requests

[dani-mp]

Please add support for inline batch requests when using GoogleGenAI with vertexai: true, so existing inline batch flows can be migrated to Vertex AI without adding GCS/BigQuery input/output plumbing.

Environment details

• Programming language: TypeScript
• OS: macOS
• Language runtime version: Node.js 22
• Package version: latest

Steps to reproduce

1. Create a GoogleGenAI client with Vertex AI enabled:

   const ai = new GoogleGenAI({
     vertexai: true,
     project: 'PROJECT_ID',
     location: 'LOCATION',
   })

2. Call ai.batches.create() with inline requests as src:

   await ai.batches.create({
     model: 'gemini-2.5-pro',
     src: [
       {
         contents: [{ text: 'Say hello' }],
       },
     ],
   })

3. Observe that inline batch requests do not appear to be supported when using vertexai: true, even though they are supported by the Gemini Developer API through the same high-level SDK method.

[Varun-S10]

Hi @dani-mp, Thank you for bringing this to our attention. We truly appreciate you flagging this issue, we will file a bug internally.