fix(openai): normalize list content from reasoning models

[ATOM00blue]

Why are these changes needed?

Some OpenAI-compatible reasoning endpoints (e.g. gpt-5, o1) return choice.message.content as a list of typed blocks instead of a string, for example:

[
  {"type": "reasoning", "text": "..."},
  {"type": "text", "text": "the actual response"}
]

In the non-streaming create() path, the text branch does content = choice.message.content or "". A non-empty list is truthy, so the raw list is assigned to content and passed straight into CreateResult, whose content field expects str | list[FunctionCall]. Callers then either get the raw list of dicts upstream or hit a Pydantic validation error, resulting in empty/malformed responses.

Repro (mocking an endpoint that returns list content) raises:

ValidationError: ... content.str
  Input should be a valid string [type=string_type, input_value=[{'type': 'reasoning', ...}], input_type=list]

This adds a small helper that, when content is a list, flattens text/output_text blocks into the content string and collects reasoning/thinking blocks into thought (matching the existing content/thought split used for reasoning_content). Unknown block types are ignored. String content is unchanged.

Related issue number

Fixes #7410

Checks

• I've included any doc changes needed for https://microsoft.github.io/autogen/. See https://github.com/microsoft/autogen/blob/main/CONTRIBUTING.md to build and test documentation locally.
• I've added tests (if relevant) corresponding to the changes introduced in this PR.
• I've made sure all auto checks have passed.

Verified locally with ruff check, ruff format --check, mypy, and pyright on the touched files, plus pytest packages/autogen-ext/tests/models/test_openai_model_client.py (54 passed). The added test test_create_normalizes_list_content fails on main and passes with this change.

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[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Adds support for OpenAI-compatible reasoning endpoints that return message.content as a list of typed blocks by normalizing it into plain text (content) and reasoning (thought).

Changes:

• Add _normalize_list_content helper to flatten block-based message.content.
• Update create() to detect list-based content and normalize it.
• Add an async test validating normalization behavior (text vs reasoning extraction).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
python/packages/autogen-ext/src/autogen_ext/models/openai/_openai_client.py	Normalizes list-based message.content into string content and optional thought during create().
python/packages/autogen-ext/tests/models/test_openai_model_client.py	Adds test coverage for list-of-blocks responses from reasoning endpoints.