feat(codex): support GPT-5.6 Max and Ultra overrides

Add "ultra" reasoning level for Codex GPT-5.6 Sol and Terra, and expose
Max for Luna (Luna falls back Ultra to Max since it is not supported
upstream). Scoped to cx/ routes only; Kiro and generic OpenAI routing
unchanged.

open-sse/handlers/chatCore.js

@@ -1,6 +1,6 @@
 import { detectFormat, getTargetFormat, resolveTransport } from "../services/provider.js";
 import { translateRequest } from "../translator/index.js";
-import { stripThinkingSuffix } from "../translator/concerns/thinkingUnified.js";
+import { applyThinking, extractThinking, stripThinkingSuffix } from "../translator/concerns/thinkingUnified.js";
 import { FORMATS } from "../translator/formats.js";
 import { normalizeClaudePassthrough } from "../translator/formats/claude.js";
 import { createStreamController } from "../utils/streamHandler.js";
@@ -28,7 +28,6 @@ import { compressWithPxpipe } from "../rtk/pxpipe.js";
 import { getCapabilitiesForModel } from "../providers/capabilities.js";
 import { stripUnsupportedModalities } from "../translator/concerns/modality.js";
 import { prefetchRemoteImages } from "../translator/concerns/prefetch.js";
-import { extractThinking } from "../translator/concerns/thinkingUnified.js";
 import { resolveSessionId } from "../utils/sessionManager.js";
 
 /**
@@ -137,6 +136,18 @@ export async function handleChatCore({ body, modelInfo, credentials, log, onCred
   if (passthrough) {
     log?.debug?.("PASSTHROUGH", `${clientTool} → ${provider} | native lossless`);
     translatedBody = { ...body, model: stripThinkingSuffix(upstreamModel) };
+    if (provider === "codex") {
+      const suffixThinking = {};
+      applyThinking(sourceFormat, upstreamModel, suffixThinking, provider);
+      if (suffixThinking.reasoning_effort) {
+        const reasoning = translatedBody.reasoning;
+        translatedBody.reasoning = {
+          ...(reasoning && typeof reasoning === "object" && !Array.isArray(reasoning) ? reasoning : {}),
+          effort: suffixThinking.reasoning_effort,
+        };
+        delete translatedBody.reasoning_effort;
+      }
+    }
     // Normalize newer Cowork/CC beta shapes (adaptive thinking, mid-conversation system) the API rejects
     if (clientTool === "claude") normalizeClaudePassthrough(translatedBody, translatedBody.model);
   } else {