fix(chat): route OAuth backend through native provider

[thakrarsagar]

Description

Fixes chat failures for the OAuth-backed LLM profile in the agentic client factory.

The provider registry already identifies this profile as a native OAuth backend, and the runtime provider factory routes it through the dedicated native provider. The agentic chat client factory missed that routing branch and fell through to a generic AsyncOpenAI client instead. With the Settings base URL set to https://chatgpt.com/backend-api, the Python backend attempted a generic chat-completions request and received an HTML browser challenge where JSON was expected.

This change routes that backend through the existing OpenAI-style adapter backed by the native provider, matching the routing used by the general LLM runtime.

Related Issues

N/A (no existing issue found)

Module(s) Affected

• agents
• api
• config
• core
• knowledge
• logging
• services
• tools
• utils
• web (Frontend)
• docs (Documentation)
• scripts
• tests
• Other: ...

Checklist

• I have read and followed the contribution guidelines.
• My code follows the project's coding standards.
• I have run pre-commit run --all-files and fixed any issues.
• I have added relevant tests for my changes.
• I have updated the documentation (if necessary).
• My changes do not introduce any new security vulnerabilities.

Additional Notes

Root cause: build_openai_client() only special-cased the Anthropic backend before constructing a generic OpenAI-compatible SDK client. Native OAuth-backed chat needs the existing native provider path instead.

Files changed:

• deeptutor/core/agentic/client.py
• tests/core/test_agentic_client_provider_kwargs.py

Validation:

• uv run --with pytest --with pytest-asyncio pytest tests/core/test_agentic_client_provider_kwargs.py -q — 12 passed
• uv run --with pre-commit pre-commit run --files deeptutor/core/agentic/client.py tests/core/test_agentic_client_provider_kwargs.py — passed