fix(codex): recover from null terminal output in Responses streams

[bananawalnut]

Summary

• recover Codex Responses streams when the SDK raises TypeError: 'NoneType' object is not iterable on a terminal null response.output
• synthesize the final response from already collected response.output_item.done events when possible
• synthesize plain assistant output from streamed text deltas when no tool calls were present
• retry once, then fall back to the existing raw create(stream=True) parser when no recoverable streamed payload exists
• add regression coverage for collected-item recovery, text-delta recovery, fallback behavior, and unrelated TypeError re-raising

Why

The ChatGPT Codex backend can close a Responses stream with a terminal frame that has no output list. OpenAI Python SDK 2.24.0 raises while iterating that field, even though Hermes may already have received usable streamed output-item events. This made Hermes abort with a non-retryable client error.

Tests

• uv run --python 3.13 --with pytest pytest tests/run_agent/test_run_agent_codex_responses.py -o 'addopts=' -q
• uv run --python 3.13 python -m py_compile agent/codex_runtime.py tests/run_agent/test_run_agent_codex_responses.py

Closes #32894

[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.