- **feat(codex):** Codex CLI compatibility shim — the Responses API `response.created`/`response.in_progress`/`response.completed` payloads now carry a `model` field (previously absent), and for Codex-CLI-originated requests it echoes the client-requested, effort-suffixed model id (e.g. `gpt-5.5-xhigh`) instead of the bare upstream id (`gpt-5.5`), so the Codex CLI status line/model button shows the active reasoning effort ([#3697](https://github.com/diegosouzapw/OmniRoute/issues/3697)). `openaiToOpenAIResponsesResponse` (`open-sse/translator/response/openai-responses.ts`) now threads the upstream model into the Responses event objects; a new `isCodexOriginatedHeaders()` (`open-sse/config/codexIdentity.ts`, reusing PR #3481's `originator`/User-Agent detection) makes chatCore's existing opt-in `echoRequestedModelName` (#1311) model-echo pipeline fire automatically for Codex clients regardless of the setting, detected by request headers so it still applies when `codex/gpt-5.5-xhigh` is routed through a combo to a non-codex upstream; `echoModelInObject`/`echoModelInSseLine` (`open-sse/services/responseModelEcho.ts`) now also rewrite the nested `response.model` field the Responses API uses. `/v1/models` still returns `models: []` for Codex (unchanged). Regression guard: `tests/unit/codex-effort-model-echo-3697.test.ts`.