Describe the bug

In main.go:3510-3525, the binary copy block opens two files and manually calls Close on every error path:

in, err := os.Open(binPath)
if err != nil { ... }
out, err := os.OpenFile(tmpNew, ...)
if err != nil { in.Close(); ... }
if _, err := io.Copy(out, in); err != nil { in.Close(); out.Close(); ... }
in.Close()
out.Close()

This is fragile — every future return needs the same dance. A close error is also discarded, masking failed flushes.

Expected behavior

Use defer for both files and report close errors (especially on out, where the close error is the only signal that pending data was actually flushed).