concatenate multple text parts for gemini models

[narengogi]

Description

When using Gemini models (especially gemini-3-pro-image-preview) that return responses with multiple text parts, the content field only contains the last text fragment instead of all text parts concatenated together.

Root Cause

In the response transformation code, when iterating through multiple text parts:

for (const part of generation.content?.parts ?? []) {
  // ...
  else if (part.text) {
    if (part.thought) {
      contentBlocks.push({ type: 'thinking', thinking: part.text });
    } else {
      content = part.text;  // ❌ BUG: OVERWRITES instead of CONCATENATING
      contentBlocks.push({ type: 'text', text: part.text });
    }
  }
}

Example

Response received:

{
  "message": {
    "content": " mostly obscured by the red one and very blurred...",  // ❌ Only last fragment
    "content_blocks": [
      { "type": "thinking", "thinking": "..." },
      { "type": "text", "text": "VERIFIED: A photorealistic rendering shows..." },  // ✅ First text part
      { "type": "text", "text": ", a blue die is on the left..." },  // ✅ Second text part
      { "type": "text", "text": " mostly obscured by the red one..." }  // ❌ Only this ends up in content
    ]
  }
}

Expected content field:

"VERIFIED: A photorealistic rendering shows..., a blue die is on the left..., mostly obscured by the red one..."

Impact

• System instructions appear to be ignored because the content field doesn't include the first text part which contains the instruction-following prefix
• The full response is available in content_blocks, but OpenAI-compatible clients expect the complete text in content
• Affects gemini-3-pro-image-preview, gemini-2.0-flash-thinking-exp, and other models that split responses into multiple text parts

Files Affected

Non-streaming responses:

• src/providers/google-vertex-ai/chatComplete.ts line 468
• src/providers/google/chatComplete.ts line 577

Streaming responses:

• src/providers/google-vertex-ai/chatComplete.ts line 644
• src/providers/google/chatComplete.ts line 704

Proposed Fix

Change from overwriting to concatenating:

// Current (buggy):
content = part.text;

// Fixed:
content = (content || '') + part.text;

Workaround for Users

Until fixed, users can manually concatenate text blocks:

const allText = message.content_blocks
  .filter(b => b.type === 'text')
  .map(b => b.text)
  .join('');

Requires x-portkey-strict-open-ai-compliance: false to receive content_blocks.