feat: enhance session UX and codex defaults

lib/agent-runtime.js

@@ -6,6 +6,7 @@ function createAgentRuntime(deps) {
     MODEL_MAP,
     loadModelConfig,
     applyCustomTemplateToSettings,
+    getDefaultCodexModel,
     loadCodexConfig,
     prepareCodexCustomRuntime,
     wsSend,
@@ -96,13 +97,13 @@ function createAgentRuntime(deps) {
         break;
     }
 
-    const effectiveModel = session.model;
+    const effectiveModel = session.model || getDefaultCodexModel();
     if (effectiveModel) {
       const raw = String(effectiveModel).trim();
       // cc-web UI supports "gpt-5.4(high)" style selection, but Codex CLI expects:
       // - model: "gpt-5.4"
       // - reasoning effort: config key `model_reasoning_effort = "high"`
-      const m = raw.match(/^(.*)\((medium|high|xhigh)\)\s*$/i);
+      const m = raw.match(/^(.*)\((low|medium|high|xhigh)\)\s*$/i);
       if (m) {
         const base = String(m[1] || '').trim();
         const lvl = String(m[2] || '').trim().toLowerCase();