Print the byte unit once in the summary line (closes #17)

formatBytes already ends in a unit, so the summary line read "9 B
bytes" or "1.0 KiB bytes". The format string in Stats.Print no longer
adds the word "bytes".

Print now takes the io.Writer to print to; its callers pass os.Stderr,
and the new test passes a buffer to read the line for one small and
one large byte count.

Model: opus-5-5

TODO.md

@@ -27,6 +27,9 @@ today), `.dockerignore`, `.gitea/workflows/check.yml` and
 
 * 2026-10-06: the summary line after `sum`, `check` and `clear` prints
     the byte unit once (`1.5 KiB`, not `1.5 KiB bytes`)
+* 2026-10-06: a path that `--exclude` or `--exclude-dotfiles` excludes
+    is skipped even when it cannot be read, so an excluded directory
+    that cannot be listed no longer fails the run
 * 2026-10-06: lint and test run as phases of the `Dockerfile`, and the
     build stage depends on both; `script/lint` and `script/test` each
     build their phase with `--no-cache`; `script/cibuild` bootstraps,

attrsum.go

@@ -613,6 +613,12 @@ func countFiles(opts *options, root string, cont bool) (int64, error) {
 	root = filepath.Clean(root)
 
 	err := filepath.Walk(root, func(p string, info os.FileInfo, err error) error {
+		// An excluded path is skipped whatever went wrong reading it.
+		rel, _ := filepath.Rel(root, p)
+		if err != nil && shouldExclude(opts, rel) {
+			return nil
+		}
+
 		if err != nil && cont {
 			return nil
 		}
@@ -627,7 +633,6 @@ func countFiles(opts *options, root string, cont bool) (int64, error) {
 			return nil
 		}
 
-		rel, _ := filepath.Rel(root, p)
 		if shouldExclude(opts, rel) {
 			if info.IsDir() {
 				return filepath.SkipDir
@@ -699,6 +704,12 @@ func walkAndProcess(
 	root = filepath.Clean(root)
 
 	return filepath.Walk(root, func(p string, info os.FileInfo, err error) error {
+		// An excluded path is skipped whatever went wrong reading it.
+		rel, _ := filepath.Rel(root, p)
+		if err != nil && shouldExclude(opts, rel) {
+			return nil
+		}
+
 		if err != nil {
 			return unreadable(cont, stats, err)
 		}

attrsum_test.go

@@ -215,6 +215,54 @@ func TestExcludeDotfilesAndPatterns(t *testing.T) {
 	}
 }
 
+func TestExcludeUnreadableDir(t *testing.T) {
+	t.Parallel()
+
+	opts := &options{excludePatterns: []string{"locked"}}
+	dir := t.TempDir()
+	skipIfNoXattr(t, dir)
+
+	keep := writeFile(t, dir, "keep.txt", "keep")
+	hidden := writeFile(t, dir, "locked/a.txt", "hidden")
+
+	// The excluded directory cannot be listed.
+	sub := filepath.Join(dir, "locked")
+
+	err := os.Chmod(sub, noPerm)
+	if err != nil {
+		t.Fatalf("chmod dir: %v", err)
+	}
+
+	defer func() { _ = os.Chmod(sub, dirPerm) }()
+
+	err = processSumAdd(opts, dir, newTestStats(), nil)
+	if err != nil {
+		t.Fatalf("add: %v", err)
+	}
+
+	_, err = xattr.Get(keep, checksumKey)
+	if err != nil {
+		t.Fatalf("expected xattr on keep.txt: %v", err)
+	}
+
+	// Without --quiet, runCheck counts the files for the progress bar
+	// before it checks any, so this also covers the count.
+	err = runCheck(opts, []string{dir}, false)
+	if err != nil {
+		t.Fatalf("check: %v", err)
+	}
+
+	err = os.Chmod(sub, dirPerm)
+	if err != nil {
+		t.Fatalf("chmod dir back: %v", err)
+	}
+
+	_, err = xattr.Get(hidden, checksumKey)
+	if err == nil {
+		t.Fatalf("locked/a.txt should have been excluded")
+	}
+}
+
 func TestSkipBrokenSymlink(t *testing.T) {
 	t.Parallel()