Git quoted paths containing literal Unicode are corrupted during decoding

Description

Quoted Git paths containing literal Unicode are corrupted by the app path helper and the legacy session-diff decoder. Both place UTF-16 code units into a byte array and then decode that array as UTF-8.

With core.quotePath=false, a filename such as 中文".txt is emitted as "中文\".txt". OpenCode decodes it as -�".txt, producing a different path. Ordinary unquoted Unicode filenames work correctly.

Steps to reproduce

From this repository's packages/app directory:

bun -e 'import { unquoteGitPath } from "./src/context/file/path"; const name = String.fromCodePoint(0x4e2d, 0x6587, 34) + ".txt"; console.log(unquoteGitPath(JSON.stringify(name)))'

Expected: 中文".txt. Actual: -�".txt.

The input was also verified against real git -c core.quotePath=false diff --numstat output on macOS. Tabs and backslashes combined with Unicode trigger the same decoding error.

This report is scoped to pathname decoding; snapshot content lookup for quoted paths has a separate limitation.

OpenCode version

1.18.28; dev commit 5cf9f517cf

Operating System

macOS 27.0 arm64, Bun 1.3.14