Issue Checklist

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• The latest version of Cherry Studio does not include the feature I am suggesting.

Platform

macOS

Version

Latest

Is your feature request related to an existing issue?

Gemini 模型返回的 thoughtSignature 目前未被持久化存储。在请求时通过中间件注入了跳过验证的魔串，但在响应时 aisdk 解析出的 providerMetadata 被丢弃了。

Desired Solution

将 Gemini 的 thoughtSignature 持久化存储到 MessageBlock 的 metadata 中：

1. Chunk 层：修改 AiSdkToChunkAdapter.ts 保留 providerMetadata
2. 类型定义：修改 Chunk 类型（TextStartChunk/TextDeltaChunk/ThinkingDeltaChunk 等）添加 providerMetadata 字段
3. Callbacks 层：修改 textCallbacks/thinkingCallbacks 接收并存储 metadata
4. 存储层：在 createMainTextBlock/createThinkingBlock 或更新时写入 metadata

Alternative Solutions

暂无

Additional Information

数据流问题：

aisdk google provider
    ↓ (每个text-start/text-delta都有providerMetadata)
AiSdkToChunkAdapter.convertAndEmitChunk()
    ↓ (只取chunk.text，丢弃chunk.providerMetadata!)
CherryStudio Chunk
    ↓
textCallbacks/thinkingCallbacks
    ↓
MainTextMessageBlock/ThinkingMessageBlock (metadata未使用)

依赖：需要等待 #12023 (Migrate to AI sdk v6) 完成后再处理