模型切换失败：target model context window is unknown

**提交人**: 用户6538
**客户端版本**: 0.1.73

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## 问题描述

在对话中切换模型时，部分模型无法切换成功，操作无响应。

## 错误信息

```
[PRECONDITION_FAILED] target model context window is unknown; runtime selection was not changed
```

来源：`maker:set-model` IPC handler

## 复现步骤

1. 在活跃会话中尝试切换到某些模型（如 `z-ai/glm-5.3-flash`）
2. 模型切换 UI 操作无效，模型未切换
3. 日志中出现上述 PRECONDITION_FAILED 错误

## 日志片段（脱敏）

```
Error occurred in handler for 'maker:set-model':
Error: [PRECONDITION_FAILED] target model context window is unknown; runtime selection was not changed

[WARN] provider change failed: ...

[INFO] modelAccess xd gateway models synced: 19
[INFO] provider-service loaded catalog from remote (model-access API)
```

## 分析

`xd gateway` 同步了 19 个模型到本地目录，但部分模型缺少 `contextWindow` 字段。Cindy 在切换模型前会检查 context window 大小，字段缺失时拒绝切换，导致用户无法使用这些模型。

## 期望行为

- 模型目录同步时应确保 `contextWindow` 字段完整；或
- 切换时若 context window 未知，给出提示而非静默失败

## 附加现象

同一会话中还出现了 API 400 错误：`Invalid chat format. Expected 'detail' field in image_url dict to be one of ['low', 'auto', 'high', 'original']`，可能也与模型/网关配置有关。
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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**: darwin arm64 (25.4.0)
**Harness**: Claude Code
**Model ID**: ` claude-sonnet-4-6 `
**界面语言**: en

Start at the maker:set-model IPC handler and trace how the xd gateway catalog and provider-service populate contextWindow. Reproduce the failure with a model such as z-ai/glm-5.3-flash, then verify that models with missing contextWindow either receive complete catalog data or produce a visible explanation instead of silently failing.

Written by the indexing model from the issue text.