$TOOL_INPUT_FILE_PATH for chat hooks doesn't work

### Describe the bug

https://code.visualstudio.com/docs/copilot/customization/hooks#_quick-start-your-first-hook

I tested the exact script provided there (prettier) and it complains
`2026-05-10 19:33:34.811 [info] [#38] [PostToolUse] Output: [error] No parser and no file path given, couldn't infer a parser.`

So I did a print of that variable, it doesn't seem to parse/pass correctly.

```
{
"hooks": {
"PostToolUse": [
{
"type": "command",
"command": "echo \"file path is $TOOL_INPUT_FILE_PATH\"",
}
]
}
}
```

2026-05-10 20:24:19.441 [info] [#42] [PostToolUse] Output: file path is

### Affected version

VS 1.119.0

### Steps to reproduce the behavior

Literally https://code.visualstudio.com/docs/copilot/customization/hooks#_quick-start-your-first-hook
And then tell copilot to make an edit and watch the github copilot chat hooks output

### Expected behavior

$TOOL_INPUT_FILE_PATH to be populated with the path of the file edited by copilot.

### Additional context

_No response_

從連結的 VS Code Copilot hooks quick-start 開始，並在 VS 1.119.0 上重現 Prettier 指令。檢查 PostToolUse hook 的輸出是否包含 TOOL_INPUT_FILE_PATH，並將其與已編輯檔案的路徑進行比較。當該變數在編輯操作中有值，且文件中的 script 執行時沒有 parser 錯誤或缺少路徑錯誤時，即表示完成。

由索引模型根據 Issue 內容生成。