Node.js's cpSync fails on Windows when the path contains non-ASCII
characters (e.g. C:\Users\Görloff) due to the \\?\ extended-length path
prefix not handling Unicode correctly. This affects both the build
script (copy-assets.cjs) and the runtime resource sync (resource-loader.ts).
Added a try/catch fallback: when cpSync throws, fall back to a manual
recursive copy using copyFileSync which handles non-ASCII paths correctly.
Changed files:
- src/resource-loader.ts: syncResourceDir() catches cpSync failure and
falls back to copyDirRecursive()
- packages/pi-coding-agent/scripts/copy-assets.cjs: all cpSync calls
wrapped in safeCpSync() with the same fallback
Fixes#1178
