Support for the `promptFeedback.blockReason` in the Gemini streaming output

[xukecheng]

Description

During the use of Gemini API, it is possible to encounter a return blockReason.

{
  "promptFeedback": {
    "blockReason": "PROHIBITED_CONTENT"
  },
  "usageMetadata": {
    "promptTokenCount": 12559,
    "totalTokenCount": 12559
  },
  "modelVersion": "gemini-1.5-flash-002"
}

However, it currently seems that there is no way to obtain the blockReason in the streaming output.

Code example

No response

AI provider

https://esm.sh/ai@4.0.1

Additional context

No response

[lgrammel]

Duplicates #4236

[lgrammel]

Identify issue type

Identified as Feature
Confidence: High

Rationale

This requests a new provider-output capability rather than reporting a failure of promised behavior. The duplicate note does not change the substantive request from an enhancement.

Evidence

• Gemini can return promptFeedback.blockReason, but the SDK does not expose it in streaming output.
• The title explicitly requests support for this additional streaming-output field.
• A maintainer notes that the request duplicates Support for the promptFeedback.blockReason in the Gemini streaming output #4236, but provides no indication that existing documented behavior is broken.