fix(codex): recover streams with null output

[mioimotoai-lgtm]

Summary

• recover Codex Responses streams when the backend sends response.output = null
• backfill streamed output items or synthesize assistant text from streamed deltas
• apply the same recovery path to auxiliary Codex calls
• add regression coverage for SDK NoneType iteration failures and direct null final output

Test Plan

• pytest tests/agent/test_codex_runtime_null_output.py -q
• hermes -z '只回答 OK' --provider openai-codex --model gpt-5.5

[alt-glitch]

Duplicate of #32884 — same Codex null output recovery (backfill streamed items, synthesize text from deltas). Also covers auxiliary_client.py. Root cause: #11179.

[teknium1]

Closing as duplicate — the Codex null-output fix has been merged via #32963 (cherry-picked from @carltonawong's PR #32890, the one Gille reviewed). Thanks for jumping on the outage so quickly; appreciate the help. Closes #11179.