// Text-only messages example
[
  { "role": "system", "content": "You are a helpful assistant." },
  { "role": "user", "content": "What is the weather like today?" },
  { "role": "assistant", "content": "The weather is sunny with a high of 75°F." }
]

// Image messages example (content as parts)
[
  { "role": "system", "content": "Describe the image briefly." },
  {
    "role": "user",
    "content": [
      { "type": "image", "mimeType": "image/png", "image": base64Png }
    ]
  }
]