Add HERMES_API_MODE env var and model.api_mode config field to let
custom OpenAI-compatible endpoints opt into codex_responses mode
without requiring the OpenAI Codex OAuth provider path.
- _get_configured_api_mode() reads HERMES_API_MODE env (precedence)
then model.api_mode from config.yaml; validates against whitelist
- Applied in both _resolve_openrouter_runtime() and
_resolve_named_custom_runtime() (original PR only covered openrouter)
- Fix _dump_api_request_debug() to show /responses URL when in
codex_responses mode instead of always showing /chat/completions
- Tests for config override, env override, invalid values, named
custom providers, and debug dump URL for both API modes
Inspired by PR #1041 by @mxyhi.
Co-authored-by: mxyhi <mxyhi@users.noreply.github.com>
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