Model API switching no longer works after an update

**提交人**: 匿名
**客户端版本**: 0.1.72

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### Summary

Switching the model API no longer works after a Cindy update.

### Expected behavior

The user should be able to switch the model API used by a conversation.

### Observed behavior

The user cannot switch the model API. This capability worked before the update.

### Impact

The user cannot choose a different model API for subsequent conversation requests.
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## 提交时的任务环境

仅代表提交时快照,不一定是故障环境。OS 来自提交客户端本机,不含 SSH 远端主机;Harness / 模型来自当前任务。与运行环境无关的反馈可忽略本段。
**版本区域**: CN
**OS**: win32 x64 (10.0.26200)
**Harness**: Codex
**Model ID**: ` gpt-5.6-sol `
**界面语言**: zh-CN

The issue names no files, tests, or entry points. Start by reproducing model API switching in Cindy 0.1.72 and compare it with the behavior before the update. Done means users can select a different model API and use it for subsequent conversation requests.

Written by the indexing model from the issue text.