[Md. Shalah Uddin (shanto462)]

Motivation & Context

Content.from_dict did not rebuild two kinds of nested content: the single Content that the OpenAI client stores in an image generation result's outputs, and the Content items that the OpenAI and Anthropic clients store in an MCP server tool result's output list. After saving and restoring messages (for example through AgentSession.to_dict() / from_dict()), these came back as plain dicts, so code that expects Content lost the data. The Responses host, for example, dropped the generated image.

Description & Review Guide

• What are the major changes? from_dict now also rebuilds a single outputs value and the items of an output list, through a new private helper, Content._from_serialized_value. These fields can also hold plain values such as tool JSON, so a mapping is rebuilt only when its type is a known content type and the rebuilt Content serializes back to the same mapping (with to_dict() or to_dict(exclude_none=False)). Otherwise, including when rebuilding raises, the original value is kept. Regression tests: a round trip of image and MCP results through Message.to_dict(), to_dict(exclude_none=False) and JSON; tool JSON that shares a content type name (kept as it is, also next to real Content in the same list); and other plain values.
• What is the impact of these changes? Image generation and MCP server tool results keep their nested Content after a round trip. The existing handling of function_call, screenshot, inputs, list outputs and items does not change.
• What do you want reviewers to focus on? The lossless check that tells serialized Content apart from tool JSON. Serialized Content always includes additional_properties, so tool JSON such as {"type": "text", "text": "x"} or {"type": "text", "value": 1} stays a plain dict. Only a mapping identical to serialized Content (for example the same dict with "additional_properties": {}) is rebuilt, since it cannot be told apart. The helper catches any exception from rebuilding, serializing or comparing, so odd tool JSON is kept instead of failing the whole load.

Related Issue

Fixes #9303

No other open PR covers this issue.

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Contribution Checklist

• The code builds clean without any errors or warnings
• All unit tests pass, and I have added new tests where possible
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[Eduard van Valkenburg (eavanvalkenburg)]

/review