## Context
nixpacks build fails with `Error: Writing app. Caused by: Permission denied (os error 13)` while copying app files, e.g. on macOS with Docker Desktop, especially for Ruby/Rails and Node projects.
## Verified resolution
Community-resolved: the failure comes from files in the build directory with restrictive permissions (e.g. `.viminfo`/`.bash_history` with 600, read-only files like pnpm's global cache links in node_modules, or Go devenv dirs with 444 perms). Fixes reporters used: delete the offending files, `chmod 600` on read-only dep dirs, or `git clean -fdx` to drop untracked files. Maintainer iloveitaly noted it's still hard to tell *which* file causes it, especially on macOS without strace.