@@ -123,6 +123,14 @@ func (sfs *worktreeFilesystem) Readlink(link string) (string, error) {
 }
 
 func (sfs *worktreeFilesystem) MkdirAll(path string, perm os.FileMode) error {
+	// MkdirAll on the worktree root is a no-op: the root always exists,
+	// so there is nothing to materialise. Mirroring the tolerance that
+	// validReadPath gives to read-side operations avoids breaking callers
+	// that walk a directory tree and pass the relative-to-root prefix
+	// ("") through to the worktree FS.
+	if path == "" || path == "." || path == "/" {
+		return nil
+	}
 	if err := sfs.validPath(path); err != nil {
 		return fmt.Errorf("mkdirall: %w", err)
 	}
 
@@ -24,6 +24,7 @@ import (
 	"github.com/go-git/go-git/v5/storage/filesystem"
 	"github.com/go-git/go-git/v5/storage/memory"
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 
 	"github.com/go-git/go-billy/v5"
 	"github.com/go-git/go-billy/v5/memfs"
@@ -3193,6 +3194,31 @@ func TestValidPath(t *testing.T) {
 	}
 }
 
+// TestWorktreeFilesystemMkdirAllRootIsNoop locks in the contract that
+// MkdirAll on a root-equivalent path is a silent no-op against the
+// wrapper. validPath itself still rejects "", ".", and "/" (see
+// TestValidPath), but MkdirAll specifically tolerates them because
+// "ensure the root exists" is always trivially satisfied.
+func TestWorktreeFilesystemMkdirAllRootIsNoop(t *testing.T) {
+	t.Parallel()
+
+	rootPaths := []string{"", ".", "/"}
+	for _, p := range rootPaths {
+		t.Run(p, func(t *testing.T) {
+			t.Parallel()
+
+			mfs := memfs.New()
+			fs := newWorktreeFilesystem(mfs, true, true)
+
+			require.NoError(t, fs.MkdirAll(p, 0o755))
+
+			entries, err := mfs.ReadDir("/")
+			require.NoError(t, err)
+			assert.Empty(t, entries, "MkdirAll(%q) must not materialise a directory entry", p)
+		})
+	}
+}
+
 var statusCodeNames = map[StatusCode]string{
 	Unmodified:         "Unmodified",
 	Untracked:          "Untracked",
Original file line number	Diff line number	Diff line change
`@@ -123,6 +123,14 @@ func (sfs *worktreeFilesystem) Readlink(link string) (string, error) {`
`123`	`123`	`}`
`124`	`124`
`125`	`125`	`func (sfs *worktreeFilesystem) MkdirAll(path string, perm os.FileMode) error {`
	`126`	`+ // MkdirAll on the worktree root is a no-op: the root always exists,`
	`127`	`+ // so there is nothing to materialise. Mirroring the tolerance that`
	`128`	`+ // validReadPath gives to read-side operations avoids breaking callers`
	`129`	`+ // that walk a directory tree and pass the relative-to-root prefix`
	`130`	`+ // ("") through to the worktree FS.`
	`131`	`+ if path == "" \|\| path == "." \|\| path == "/" {`
	`132`	`+ return nil`
	`133`	`+ }`
`126`	`134`	`if err := sfs.validPath(path); err != nil {`
`127`	`135`	`return fmt.Errorf("mkdirall: %w", err)`
`128`	`136`	`}`