Reorganize AI integration-related test fixtures

[ericapisani]

Context: #5937

Right now, a large number of our pytest fixtures live in the global conftest.py file. For maintainability reasons, it'd be better to move provider-specific (or just AI integration-specific) fixtures into separate conftest.py files and load them into the global conftest.py using pytest_plugins.

[linear-code]

PY-2296

[mizoz]

Hi! I'd love to contribute. Could you assign this issue to me?

[omribz156]

I traced the fixture cluster and this looks like a good small first split.

The cleanest scoped pass I see is to move the MCP transport helpers and AI model response fixtures out of the global tests/conftest.py into the integrations layer, where the current users already live:

• MCP/FastMCP helpers: stdio, json_rpc, json_rpc_sse, and the selector/payload helpers
• AI response fixtures used by OpenAI, OpenAI Agents, LiteLLM, and LangChain tests

That would leave the default behavior unchanged for integration tests while cutting down the global conftest surface. I also noticed the contribution guide asks for prior maintainer discussion before PR work, so I am checking here before opening anything.

This would be Codex-assisted, with the final patch reviewed locally and kept to that fixture move only.

[ericapisani]

Hi @omribz156 ,

Thanks for offering to take a look at this, the split that you've proposed looks good. I'll assign the issue to you, and don't hesitate to reach out if you have any questions as you dig into this.