Answer on a plain OpenAI key from the Microsoft Agent Framework Bot

[asasemahmed]

What this changes

Picked with a plain OpenAI key, the Microsoft Agent Framework Bot fails every run:

openai.APIConnectionError: Connection error.

Compose passes the picked harness OPENAI_BASE_URL: ${OPENAI_CONTAINER_BASE_URL:-${OPENAI_BASE_URL:-}},
and for a plain OpenAI key that is empty. OpenAIChatClient(model) leaves the base URL to the
OpenAI SDK, which reads OPENAI_BASE_URL and falls back to https://api.openai.com/v1 only when it
is absent. Given "", the request has no host.

The Anthropic branch just above already handles exactly this, since #613: "Compose exports missing
overrides as ""; the SDK only defaults an absent URL." The OpenAI branch now does the same, passing
base_url=(OPENAI_BASE_URL or "").strip() or "https://api.openai.com/v1". An OpenAI-compatible
endpoint is passed through as before.

#649 edits the provider and model lines of this file; this change is a separate hunk below them.

Where it runs

• New state that outlives a request? None. The client is chosen once at import.
• What happens on the second replica? The same, from the same environment.
• Anything serialised? No.
• Anything fanned out to a browser? No.
• New listener, port, or schedule? No.

Boundary and audit

• Every acting call still goes through the gateway: nothing on the server changes, and the
  harness still refuses a request without the server's token.
• New refusals and new failures each write a row: none added.
• Nothing new is trusted from the client.

Changelog

• An entry in CHANGELOG.md under Unreleased.

Proof

• New test_an_openai_key_uses_the_official_endpoint_when_compose_sets_a_blank_url, the twin of
  the Anthropic test above it: the real framework and OpenAI clients, with only the transport
  replaced. It asserts the request went to https://api.openai.com/v1/responses with
  Bearer test-key, and a finished run. The OpenAI SDK sends through httpx2, not httpx, so this
  test patches httpx2's transport. Patching httpx's would let the request out.
• Python 3.12, the CI step's commands, run in a container with no network: this branch
  6 passed. With src from main: 1 failed, 5 passed, the new case. With the transport left
  alone, main fails with the APIConnectionError above.
• Versions pip resolved: agent-framework-core 1.19.0, agent-framework-openai 1.14.4,
  agent-framework-ag-ui 1.4.0, openai 3.19.2, httpx2 2.13.1.
• Not run: a real OpenAI key, and the published image.