fix(api): allow nested dicts in ChatMessage.content for multimodal requests

[creedx12]

Problem

ChatMessage.content is typed Optional[Union[str, List[Dict[str, str]]]] (chat/openai/schema.py). The OpenAI multimodal format nests a dict under image_url:

{"type": "image_url", "image_url": {"url": "..."}}

Dict[str, str] rejects that nested object, so FastAPI returns 422 before the handler runs — every vision request fails at the schema layer, even though VLM routing exists internally.

Fix

Widen the value type to Any (List[Dict[str, Any]]). Any is already imported. One-line change.

Present on main (0.5.3).

Summary by CodeRabbit

• Improvements
  • Chat messages now support more flexible content structures and richer data formats for enhanced compatibility.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 6a4c0a3e-f0df-439a-8033-5ef0334621c3

📥 Commits

Reviewing files that changed from the base of the PR and between 4f8e9ef and dd2666d.

📒 Files selected for processing (1)

• src/mlx_omni_server/chat/openai/schema.py

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📝 Walkthrough

Walkthrough

The type annotation for ChatMessage.content in the OpenAI schema is widened from Optional[Union[str, List[Dict[str, str]]]] to Optional[Union[str, List[Dict[str, Any]]]], allowing dictionary values in the list form to hold any type rather than only strings.

Changes

ChatMessage Schema Type Widening

Layer / File(s)	Summary
ChatMessage.content field type src/mlx_omni_server/chat/openai/schema.py	content field type changes from List[Dict[str, str]] to List[Dict[str, Any]] for the list branch, widening Pydantic validation to accept non-string dictionary values.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~2 minutes

Poem

A bunny once hopped through a schema one day,
And found that the strings were too strict in their way.
"Let Any come through!" cried the rabbit with glee,
One character changed — str swapped out for Any.
Now content flows freely, as typed as can be! 🐇✨

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and specifically describes the main change: updating ChatMessage.content to accept nested dictionaries for multimodal requests.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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