Extensions recieve toolArgs as a string rather than an object

### Short summary

_No response_

### Affected version or release

v1.1.10

### Installation context

downloaded from website, windows-x64

### What happened?

Hi devs, thanks for your hard work!
From my ai chat -
In `onPreToolUse` the host delivers `toolArgs` as a JSON-encoded *string*, but the SDK docs (`agent-author.md`, `examples.md`) show object access (`args.command`, `...input.toolArgs`) and the `.d.ts` types expose it as `unknown`/`JsonValue`. This means all documented object-style examples silently return nothing. Either deliver a parsed object or parse/normalize in the SDK and document the contract explicitly.

### Steps to reproduce

My extension requires this in order to function:

function toolTargets(toolName, args) {
if (!args) return [];
// The RPC layer delivers toolArgs as a JSON-encoded string; parse it to
// an object so we can inspect .path/.paths/.pattern.
if (typeof args === "string") {
try {
args = JSON.parse(args);
} catch {
return [];
}
}

### Expected behavior

I think args should be passed as objects, but at a minimum when the ai references the documents and then writes and extension, it should copy something that works correctly.

### Additional context

_No response_

先从 onPreToolUse RPC 路径和 .d.ts 类型入手，然后将 agent-author.md 和 examples.md 中记录的契约与 v1.1.10 所描述的字符串 payload 进行对比。只有当主机或 SDK 契约和文档能够一致地说明并支持可用的 toolArgs 形态（包括文档所述的对象式访问）时，才算完成。

由索引模型根据 Issue 内容生成。