fix: omit empty tools for Codex Responses

[roycepersonalassistant]

Summary

• omit the Responses API tools kwarg when no converted tools are available
• keep tool_choice and parallel_tool_calls gated on actual tools
• add regression coverage for tools=None

Test plan

• ./scripts/run_tests.sh tests/agent/transports/test_codex_transport.py
• ./scripts/run_tests.sh tests/run_agent/test_run_agent_codex_responses.py tests/run_agent/test_413_compression.py tests/agent/transports/test_codex_transport.py
• git diff --check

[teknium1]

Thanks — closing as already fixed on main.

The tools=None TypeError on openai-codex when no tools are registered is resolved by fc47b7285 (omit the tools key entirely from Codex Responses kwargs when empty) plus 68d547281 / #3820 (omit tools instead of sending None). Both are on main.

Your fix targets the same already-hardened path. Authorship stays in your branch; crediting your report in the umbrella issue #33932. Appreciate it.