diff --git a/.core/TODO.md b/.core/TODO.md
index e69de29b..874ce2e8 100644
--- a/.core/TODO.md
+++ b/.core/TODO.md
@@ -0,0 +1 @@
+- @security pkg/display/display.go:954 — WebSocket layout commands still coerce missing or malformed numeric fields to zero instead of rejecting the request.
diff --git a/pkg/environment/service.go b/pkg/environment/service.go
index 8aed0b03..18d9f93b 100644
--- a/pkg/environment/service.go
+++ b/pkg/environment/service.go
@@ -3,6 +3,7 @@ package environment
 
 import (
 	"context"
+	"path/filepath"
 	"strings"
 	"sync"
 
@@ -42,7 +43,11 @@ func (s *Service) OnStartup(_ context.Context) core.Result {
 	})
 	s.Core().Action("environment.openFileManager", func(_ context.Context, opts core.Options) core.Result {
 		t, _ := opts.Get("task").Value.(TaskOpenFileManager)
-		if err := s.platform.OpenFileManager(t.Path, t.Select); err != nil {
+		path, err := validatedOpenFileManagerPath(t.Path)
+		if err != nil {
+			return core.Result{Value: err, OK: false}
+		}
+		if err := s.platform.OpenFileManager(path, t.Select); err != nil {
 			return core.Result{Value: err, OK: false}
 		}
 		return core.Result{OK: true}
@@ -160,6 +165,21 @@ func normalizeTheme(theme string) (string, error) {
 	}
 }
 
+func validatedOpenFileManagerPath(raw string) (string, error) {
+	trimmed := strings.TrimSpace(raw)
+	if trimmed == "" {
+		return "", coreerr.E("environment.openFileManager", "path is required", nil)
+	}
+	if strings.ContainsRune(trimmed, '\x00') {
+		return "", coreerr.E("environment.openFileManager", "path contains a null byte", nil)
+	}
+	cleaned := filepath.Clean(trimmed)
+	if !filepath.IsAbs(cleaned) {
+		return "", coreerr.E("environment.openFileManager", "path must be absolute", nil)
+	}
+	return cleaned, nil
+}
+
 func themeName(isDark bool) string {
 	if isDark {
 		return "dark"
diff --git a/pkg/environment/service_test.go b/pkg/environment/service_test.go
index ff2bb680..12883f75 100644
--- a/pkg/environment/service_test.go
+++ b/pkg/environment/service_test.go
@@ -3,6 +3,7 @@ package environment
 
 import (
 	"context"
+	"path/filepath"
 	"sync"
 	"testing"
 
@@ -17,6 +18,8 @@ type mockPlatform struct {
 	info              EnvironmentInfo
 	accentColour      string
 	openFMErr         error
+	openFMPath        string
+	openFMSelect      bool
 	focusFollowsMouse bool
 	themeHandler      func(isDark bool)
 	mu                sync.Mutex
@@ -27,6 +30,8 @@ func (m *mockPlatform) Info() EnvironmentInfo      { return m.info }
 func (m *mockPlatform) AccentColour() string       { return m.accentColour }
 func (m *mockPlatform) HasFocusFollowsMouse() bool { return m.focusFollowsMouse }
 func (m *mockPlatform) OpenFileManager(path string, selectFile bool) error {
+	m.openFMPath = path
+	m.openFMSelect = selectFile
 	return m.openFMErr
 }
 func (m *mockPlatform) OnThemeChange(handler func(isDark bool)) func() {
@@ -100,11 +105,22 @@ func TestQueryAccentColour_Good(t *testing.T) {
 }
 
 func TestTaskOpenFileManager_Good(t *testing.T) {
-	_, c := newTestService(t)
+	mock, c := newTestService(t)
 	r := c.Action("environment.openFileManager").Run(context.Background(), core.NewOptions(
 		core.Option{Key: "task", Value: TaskOpenFileManager{Path: "/tmp", Select: true}},
 	))
 	require.True(t, r.OK)
+	assert.Equal(t, filepath.Clean("/tmp"), mock.openFMPath)
+	assert.True(t, mock.openFMSelect)
+}
+
+func TestTaskOpenFileManager_Bad_InvalidPath(t *testing.T) {
+	_, c := newTestService(t)
+	r := c.Action("environment.openFileManager").Run(context.Background(), core.NewOptions(
+		core.Option{Key: "task", Value: TaskOpenFileManager{Path: "../tmp", Select: false}},
+	))
+	assert.False(t, r.OK)
+	assert.Contains(t, r.Value.(error).Error(), "path must be absolute")
 }
 
 func TestThemeChange_ActionBroadcast_Good(t *testing.T) {