Fix filepath.Rel error wrap to include the actual error

The glob loops in Local.Upload, Remote.Upload and findMatchedFiles
wrapped the outer err (nil at that point) instead of the local e
returned by filepath.Rel, so a rel failure would render
%!w(<nil>) and lose the cause. Diagnostic-only, no behaviour change.

Follow-up to review feedback on #352.

Author: paskal

pkg/executor/local.go

@@ -96,7 +96,7 @@ func (l *Local) Upload(_ context.Context, src, dst string, opts *UpDownOpts) (er
 	for _, match := range matches {
 		relPath, e := filepath.Rel(filepath.Dir(src), match)
 		if e != nil {
-			return fmt.Errorf("failed to build relative path for %s: %w", match, err)
+			return fmt.Errorf("failed to build relative path for %s: %w", match, e)
 		}
 		// check source file info; check exclusion before the stat error so an excluded broken symlink
 		// is skipped instead of failing the whole upload

pkg/executor/remote.go

@@ -75,7 +75,7 @@ func (ex *Remote) Upload(ctx context.Context, local, remote string, opts *UpDown
 	for _, match := range matches {
 		relPath, e := filepath.Rel(filepath.Dir(local), match)
 		if e != nil {
-			return fmt.Errorf("failed to build relative path for %s: %w", match, err)
+			return fmt.Errorf("failed to build relative path for %s: %w", match, e)
 		}
 		// matches are local paths, stat them so directory excludes (e.g. "subdir/*") skip a matched directory
 		matchInfo, statErr := os.Stat(match)
@@ -674,7 +674,7 @@ func (ex *Remote) findMatchedFiles(remote string, excl []string) ([]string, erro
 	for _, match := range matches {
 		relPath, e := filepath.Rel(filepath.Dir(remote), match)
 		if e != nil {
-			return nil, fmt.Errorf("failed to build relative path for %s: %w", match, err)
+			return nil, fmt.Errorf("failed to build relative path for %s: %w", match, e)
 		}
 		// matches are remote paths, stat them so directory excludes (e.g. "subdir/*") skip a matched directory
 		matchInfo, statErr := sftpClient.Stat(match)