fix(custom): normalize responses api mode alias

[LeonSGP43]

Summary

• normalize the user-facing responses api_mode alias to codex_responses for custom runtime resolution
• accept AIAgent(api_mode="responses") and route request dumps / live requests to /responses instead of silently falling back to /chat/completions
• add regressions for runtime-provider normalization and request-dump URL selection

Testing

• uv run --frozen pytest -o addopts= tests/hermes_cli/test_runtime_provider_resolution.py -k 'model_config_api_mode or responses_alias_normalized'
• uv run --frozen pytest -o addopts= tests/run_agent/test_run_agent_codex_responses.py -k 'dump_api_request_debug_uses_responses_url or dump_api_request_debug_normalizes_responses_alias'
• uv run --frozen ruff check agent/agent_init.py hermes_cli/runtime_provider.py tests/hermes_cli/test_runtime_provider_resolution.py tests/run_agent/test_run_agent_codex_responses.py
• git diff --check

Fixes #33600

[teknium1]

Thanks for the focused alias and regression work. Current main has a newer plain-custom routing guard that this patch needs to account for.

Problems

• Mapping responses to codex_responses in hermes_cli/runtime_provider.py is later cleared for non-direct-OpenAI/xAI plain custom URLs by _resolve_plain_custom_api_mode() (hermes_cli/runtime_provider.py:151-161). The provider=custom return path uses that helper at hermes_cli/runtime_provider.py:1178-1184, so the reported config flow would still resolve to chat_completions.
• Current coverage deliberately asserts this behavior for a localhost custom relay at tests/hermes_cli/test_runtime_provider_resolution.py:1346-1365, following commit 0e4c879a3.

Suggested changes

• Please reconcile an explicit Responses opt-in with the newer relay-safety behavior, then add a config-to-runtime regression for the approved behavior. The direct constructor/debug-dump test does not cover that resolver path.

Automated hermes-sweeper review.

[teknium1]

On current main, this resulting codex_responses value is cleared for non-direct-OpenAI/xAI plain custom URLs by _resolve_plain_custom_api_mode() (hermes_cli/runtime_provider.py:154-161). Please reconcile that newer safety behavior and cover the plain-custom config path; this alias alone will not change its resolved request mode.