OpenAI Responses JSON-stringifies image media returned from tool results

[kitlangton]

Problem

The native OpenAI Responses protocol lowers every tool-result into a string via toolResultText. For content-typed tool results, that JSON-stringifies the whole content array, including base64 image data URLs, into function_call_output.output.

That shape is wrong for screenshot/read tool results. It can make the request invalid or oversized, and the provider may only surface a generic stream error.

Expected

• Tool-result image media should be emitted as structured OpenAI Responses input_image content.
• Text/json/error tool results should keep the existing string behavior.
• Unsupported non-image tool-result media should fail clearly.

PR

• fix(llm): emit structured input_image content for tool-result media in OpenAI Responses #28754

[github-actions]

This issue might be a duplicate of (or closely related to) an existing issue. Please check:

• Anthropic Messages JSON-stringifies image media returned from tool results #28861: Anthropic Messages JSON-stringifies image media returned from tool results — same root symptom (toolResultText JSON-stringifying image content from tool results), but for the Anthropic provider instead of OpenAI Responses.

If these are intentionally tracked separately by provider, feel free to disregard.