fix: stabilize /model reasoning-effort selection (v0.3.5)

Keep pending model outside the picker map, omit undefined reasoningEffort in selectModel payload, auto-apply single-effort models, and surface RPC errors.

Co-authored-by: Cursor <cursoragent@cursor.com>

lib/commands.js

@@ -53,7 +53,12 @@ export const MSG = {
     MODEL_SET(selected) {
         return `已切换模型：${selected}\n下一回合生效。`;
     },
-    MODEL_FAILED: '切换模型失败。请稍后重试或在 Web 中切换。',
+    MODEL_FAILED(detail) {
+        const tip = '切换模型失败。请稍后重试或在 Web 中切换。';
+        if (!detail)
+            return tip;
+        return `${tip}\n详情：${detail}`;
+    },
     unknown(command) {
         return `未知命令 ${command}。发送 /help 查看可用命令。`;
     },