Deflake realtime handoff steering test

[felixxia-oai]

Summary

• keep the realtime mock websocket open for the handoff steering test after scripted responses
• avoid racing the mock server close before the standalone handoff append is observed, which was showing up as a Windows timeout in CI

Details:
Failures in samples seem to be caused by:

1. The mock websocket sends conversation.handoff.requested.
2. The mock immediately closes the websocket because start_websocket_server(...) defaults to close_after_requests: true.
3. On Windows, that close often surfaces as os error 10053 / 10054.
4. The realtime stream shuts down before the routed handoff finishes creating/steering the follow-up request.
5. The test waits for the expected follow-up event and times out.

The PR changes only step 2: for this test, the mock websocket stays open after sending the scripted handoff event. The same handoff event is still sent, and the test still asserts the important steering behavior:

1. first Responses request has the original prompt
2. first request does not contain realtime delegation
3. second Responses request does contain the realtime delegation

Validation

• just fmt
• just test -p codex-core --test all suite::realtime_conversation::inbound_handoff_request_steers_active_turn

Recent CI failures with the same signature

• https://github.com/openai/codex/actions/runs/27538033492/job/81392362858

  • 2026-06-15, [codex] update multi-agent v2 prompts
  • same test failed after conversation.handoff.requested; websocket read failed with os error 10053

• https://github.com/openai/codex/actions/runs/27543877820/job/81412200651

  • 2026-06-15, feat: dispatch queued user messages through core idle extensions
  • same test failed; websocket read failed with os error 10054

• https://github.com/openai/codex/actions/runs/27544342375/job/81413801641

  • 2026-06-15, [codex] Make marketplace loading capability aware
  • same test failed; websocket read failed with os error 10053

[felixxia-oai]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Breezy!

Reviewed commit: 7b622835b8

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