brightness: add udev monitor, bind OSDs to netlink events

fixes #863

core/go.mod

@@ -11,6 +11,8 @@ require (
 	github.com/fsnotify/fsnotify v1.9.0
 	github.com/godbus/dbus/v5 v5.2.0
 	github.com/holoplot/go-evdev v0.0.0-20250804134636-ab1d56a1fe83
+	github.com/pilebones/go-udev v0.9.1
+	github.com/sblinch/kdl-go v0.0.0-20250930225324-bf4099d4614a
 	github.com/spf13/cobra v1.10.1
 	github.com/stretchr/testify v1.11.1
 	golang.org/x/exp v0.0.0-20251125195548-87e1e737ad39
@@ -32,7 +34,6 @@ require (
 	github.com/kevinburke/ssh_config v1.4.0 // indirect
 	github.com/klauspost/cpuid/v2 v2.3.0 // indirect
 	github.com/pjbgf/sha1cd v0.5.0 // indirect
-	github.com/sblinch/kdl-go v0.0.0-20250930225324-bf4099d4614a // indirect
 	github.com/sergi/go-diff v1.4.0 // indirect
 	github.com/stretchr/objx v0.5.3 // indirect
 	golang.org/x/crypto v0.45.0 // indirect

core/go.sum

@@ -24,16 +24,12 @@ github.com/charmbracelet/lipgloss v1.1.0 h1:vYXsiLHVkK7fp74RkV7b2kq9+zDLoEU4MZoF
 github.com/charmbracelet/lipgloss v1.1.0/go.mod h1:/6Q8FR2o+kj8rz4Dq0zQc3vYf7X+B0binUUBwA0aL30=
 github.com/charmbracelet/log v0.4.2 h1:hYt8Qj6a8yLnvR+h7MwsJv/XvmBJXiueUcI3cIxsyig=
 github.com/charmbracelet/log v0.4.2/go.mod h1:qifHGX/tc7eluv2R6pWIpyHDDrrb/AG71Pf2ysQu5nw=
-github.com/charmbracelet/x/ansi v0.11.0 h1:uuIVK7GIplwX6UBIz8S2TF8nkr7xRlygSsBRjSJqIvA=
-github.com/charmbracelet/x/ansi v0.11.0/go.mod h1:uQt8bOrq/xgXjlGcFMc8U2WYbnxyjrKhnvTQluvfCaE=
 github.com/charmbracelet/x/ansi v0.11.2 h1:XAG3FSjiVtFvgEgGrNBkCNNYrsucAt8c6bfxHyROLLs=
 github.com/charmbracelet/x/ansi v0.11.2/go.mod h1:9tY2bzX5SiJCU0iWyskjBeI2BRQfvPqI+J760Mjf+Rg=
 github.com/charmbracelet/x/cellbuf v0.0.14 h1:iUEMryGyFTelKW3THW4+FfPgi4fkmKnnaLOXuc+/Kj4=
 github.com/charmbracelet/x/cellbuf v0.0.14/go.mod h1:P447lJl49ywBbil/KjCk2HexGh4tEY9LH0/1QrZZ9rA=
 github.com/charmbracelet/x/term v0.2.2 h1:xVRT/S2ZcKdhhOuSP4t5cLi5o+JxklsoEObBSgfgZRk=
 github.com/charmbracelet/x/term v0.2.2/go.mod h1:kF8CY5RddLWrsgVwpw4kAa6TESp6EB5y3uxGLeCqzAI=
-github.com/clipperhouse/displaywidth v0.5.0 h1:AIG5vQaSL2EKqzt0M9JMnvNxOCRTKUc4vUnLWGgP89I=
-github.com/clipperhouse/displaywidth v0.5.0/go.mod h1:R+kHuzaYWFkTm7xoMmK1lFydbci4X2CicfbGstSGg0o=
 github.com/clipperhouse/displaywidth v0.6.0 h1:k32vueaksef9WIKCNcoqRNyKbyvkvkysNYnAWz2fN4s=
 github.com/clipperhouse/displaywidth v0.6.0/go.mod h1:R+kHuzaYWFkTm7xoMmK1lFydbci4X2CicfbGstSGg0o=
 github.com/clipperhouse/stringish v0.1.1 h1:+NSqMOr3GR6k1FdRhhnXrLfztGzuG+VuFDfatpWHKCs=
@@ -43,8 +39,6 @@ github.com/clipperhouse/uax29/v2 v2.3.0/go.mod h1:Wn1g7MK6OoeDT0vL+Q0SQLDz/KpfsV
 github.com/cloudflare/circl v1.6.1 h1:zqIqSPIndyBh1bjLVVDHMPpVKqp8Su/V+6MeDzzQBQ0=
 github.com/cloudflare/circl v1.6.1/go.mod h1:uddAzsPgqdMAYatqJ0lsjX1oECcQLIlRpzZh3pJrofs=
 github.com/cpuguy83/go-md2man/v2 v2.0.6/go.mod h1:oOW0eioCTA6cOiMLiUPZOpcVxMig6NIQQ7OS05n1F4g=
-github.com/cyphar/filepath-securejoin v0.6.0 h1:BtGB77njd6SVO6VztOHfPxKitJvd/VPT+OFBFMOi1Is=
-github.com/cyphar/filepath-securejoin v0.6.0/go.mod h1:A8hd4EnAeyujCJRrICiOWqjS1AX0a9kM5XL+NwKoYSc=
 github.com/cyphar/filepath-securejoin v0.6.1 h1:5CeZ1jPXEiYt3+Z6zqprSAgSWiggmpVyciv8syjIpVE=
 github.com/cyphar/filepath-securejoin v0.6.1/go.mod h1:A8hd4EnAeyujCJRrICiOWqjS1AX0a9kM5XL+NwKoYSc=
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
@@ -62,19 +56,14 @@ github.com/gliderlabs/ssh v0.3.8 h1:a4YXD1V7xMF9g5nTkdfnja3Sxy1PVDCj1Zg4Wb8vY6c=
 github.com/gliderlabs/ssh v0.3.8/go.mod h1:xYoytBv1sV0aL3CavoDuJIQNURXkkfPA/wxQ1pL1fAU=
 github.com/go-git/gcfg/v2 v2.0.2 h1:MY5SIIfTGGEMhdA7d7JePuVVxtKL7Hp+ApGDJAJ7dpo=
 github.com/go-git/gcfg/v2 v2.0.2/go.mod h1:/lv2NsxvhepuMrldsFilrgct6pxzpGdSRC13ydTLSLs=
-github.com/go-git/go-billy/v6 v6.0.0-20251111123000-fb5ff8f3f0b0 h1:EC9n6hr6yKDoVJ6g7Ko523LbbceJfR0ohbOp809Fyf4=
-github.com/go-git/go-billy/v6 v6.0.0-20251111123000-fb5ff8f3f0b0/go.mod h1:E3VhlS+AKkrq6ZNn1axE2/nDRJ87l1FJk9r5HT2vPX0=
 github.com/go-git/go-billy/v6 v6.0.0-20251126203821-7f9c95185ee0 h1:eY5aB2GXiVdgTueBcqsBt53WuJTRZAuCdIS/86Pcq5c=
 github.com/go-git/go-billy/v6 v6.0.0-20251126203821-7f9c95185ee0/go.mod h1:0NjwVNrwtVFZBReAp5OoGklGJIgJFEbVyHneAr4lc8k=
 github.com/go-git/go-git-fixtures/v5 v5.1.1 h1:OH8i1ojV9bWfr0ZfasfpgtUXQHQyVS8HXik/V1C099w=
 github.com/go-git/go-git-fixtures/v5 v5.1.1/go.mod h1:Altk43lx3b1ks+dVoAG2300o5WWUnktvfY3VI6bcaXU=
-github.com/go-git/go-git/v6 v6.0.0-20251112161705-8cc3e21f07a9 h1:SOFrnF9LCssC6q6Rb0084Bzg2aBYbe8QXv9xKGXmt/w=
-github.com/go-git/go-git/v6 v6.0.0-20251112161705-8cc3e21f07a9/go.mod h1:0wtvm/JfPC9RFVEAP3ks0ec5h64/qmZkTTUE3pjz7Hc=
 github.com/go-git/go-git/v6 v6.0.0-20251128074608-48f817f57805 h1:jxQ3BzYeErNRvlI/4+0mpwqMzvB4g97U+ksfgvrUEbY=
 github.com/go-git/go-git/v6 v6.0.0-20251128074608-48f817f57805/go.mod h1:dIwT3uWK1ooHInyVnK2JS5VfQ3peVGYaw2QPqX7uFvs=
 github.com/go-logfmt/logfmt v0.6.1 h1:4hvbpePJKnIzH1B+8OR/JPbTx37NktoI9LE2QZBBkvE=
 github.com/go-logfmt/logfmt v0.6.1/go.mod h1:EV2pOAQoZaT1ZXZbqDl5hrymndi4SY9ED9/z6CO0XAk=
-github.com/godbus/dbus/v5 v5.1.0 h1:4KLkAxT3aOY8Li4FRJe/KvhoNFFxo0m6fNuFUO8QJUk=
 github.com/godbus/dbus/v5 v5.1.0/go.mod h1:xhWf0FNVPg57R7Z0UbKHbJfkEywrmjJnf7w5xrFpKfA=
 github.com/godbus/dbus/v5 v5.2.0 h1:3WexO+U+yg9T70v9FdHr9kCxYlazaAXUhx2VMkbfax8=
 github.com/godbus/dbus/v5 v5.2.0/go.mod h1:3AAv2+hPq5rdnr5txxxRwiGjPXamgoIHgz9FPBfOp3c=
@@ -95,8 +84,9 @@ github.com/kr/pretty v0.1.0/go.mod h1:dAy3ld7l9f0ibDNOQOHHMYYIIbhfbHSm3C4ZsoJORN
 github.com/kr/pretty v0.3.1 h1:flRD4NNwYAUpkphVc1HcthR4KEIFJ65n8Mw5qdRn3LE=
 github.com/kr/pretty v0.3.1/go.mod h1:hoEshYVHaxMs3cyo3Yncou5ZscifuDolrwPKZanG3xk=
 github.com/kr/pty v1.1.1/go.mod h1:pFQYn66WHrOpPYNljwOMqo10TkYh1fy3cYio2l3bCsQ=
-github.com/kr/text v0.1.0 h1:45sCR5RtlFHMR4UwH9sdQ5TC8v0qDQCHnXt+kaKSTVE=
 github.com/kr/text v0.1.0/go.mod h1:4Jbv+DJW3UT/LiOwJeYQe1efqtUx/iVham/4vfdArNI=
+github.com/kr/text v0.2.0 h1:5Nx0Ya0ZqY2ygV366QzturHI13Jq95ApcVaJBhpS+AY=
+github.com/kr/text v0.2.0/go.mod h1:eLer722TekiGuMkidMxC/pM04lWEeraHUUmBw8l2grE=
 github.com/lucasb-eyer/go-colorful v1.3.0 h1:2/yBRLdWBZKrf7gB40FoiKfAWYQ0lqNcbuQwVHXptag=
 github.com/lucasb-eyer/go-colorful v1.3.0/go.mod h1:R4dSotOR9KMtayYi1e77YzuveK+i7ruzyGqttikkLy0=
 github.com/mattn/go-isatty v0.0.20 h1:xfD0iDuEKnDkl03q4limB+vH+GxLEtL/jb4xVJSWWEY=
@@ -111,6 +101,8 @@ github.com/muesli/cancelreader v0.2.2 h1:3I4Kt4BQjOR54NavqnDogx/MIoWBFa0StPA8ELU
 github.com/muesli/cancelreader v0.2.2/go.mod h1:3XuTXfFS2VjM+HTLZY9Ak0l6eUKfijIfMUZ4EgX0QYo=
 github.com/muesli/termenv v0.16.0 h1:S5AlUN9dENB57rsbnkPyfdGuWIlkmzJjbFf0Tf5FWUc=
 github.com/muesli/termenv v0.16.0/go.mod h1:ZRfOIKPFDYQoDFF4Olj7/QJbW60Ol/kL1pU3VfY/Cnk=
+github.com/pilebones/go-udev v0.9.1 h1:uN72M1C1fgzhsVmBGEM8w9RD1JY4iVsPZpr+Z6rb3O8=
+github.com/pilebones/go-udev v0.9.1/go.mod h1:Bgcl07crebF3JSeS4+nuaRvhWFdCeFoBhXXeAp93XNo=
 github.com/pjbgf/sha1cd v0.5.0 h1:a+UkboSi1znleCDUNT3M5YxjOnN1fz2FhN48FlwCxs0=
 github.com/pjbgf/sha1cd v0.5.0/go.mod h1:lhpGlyHLpQZoxMv8HcgXvZEhcGs0PG/vsZnEJ7H0iCM=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
@@ -139,12 +131,8 @@ github.com/stretchr/testify v1.11.1 h1:7s2iGBzp5EwR7/aIZr8ao5+dra3wiQyKjjFuvgVKu
 github.com/stretchr/testify v1.11.1/go.mod h1:wZwfW3scLgRK+23gO65QZefKpKQRnfz6sD981Nm4B6U=
 github.com/xo/terminfo v0.0.0-20220910002029-abceb7e1c41e h1:JVG44RsyaB9T2KIHavMF/ppJZNG9ZpyihvCd0w101no=
 github.com/xo/terminfo v0.0.0-20220910002029-abceb7e1c41e/go.mod h1:RbqR21r5mrJuqunuUZ/Dhy/avygyECGrLceyNeo4LiM=
-golang.org/x/crypto v0.44.0 h1:A97SsFvM3AIwEEmTBiaxPPTYpDC47w720rdiiUvgoAU=
-golang.org/x/crypto v0.44.0/go.mod h1:013i+Nw79BMiQiMsOPcVCB5ZIJbYkerPrGnOa00tvmc=
 golang.org/x/crypto v0.45.0 h1:jMBrvKuj23MTlT0bQEOBcAE0mjg8mK9RXFhRH6nyF3Q=
 golang.org/x/crypto v0.45.0/go.mod h1:XTGrrkGJve7CYK7J8PEww4aY7gM3qMCElcJQ8n8JdX4=
-golang.org/x/exp v0.0.0-20251113190631-e25ba8c21ef6 h1:zfMcR1Cs4KNuomFFgGefv5N0czO2XZpUbxGUy8i8ug0=
-golang.org/x/exp v0.0.0-20251113190631-e25ba8c21ef6/go.mod h1:46edojNIoXTNOhySWIWdix628clX9ODXwPsQuG6hsK0=
 golang.org/x/exp v0.0.0-20251125195548-87e1e737ad39 h1:DHNhtq3sNNzrvduZZIiFyXWOL9IWaDPHqTnLJp+rCBY=
 golang.org/x/exp v0.0.0-20251125195548-87e1e737ad39/go.mod h1:46edojNIoXTNOhySWIWdix628clX9ODXwPsQuG6hsK0=
 golang.org/x/net v0.47.0 h1:Mx+4dIFzqraBXUugkia1OOvlD6LemFo1ALMHjrXDOhY=

core/internal/server/brightness/manager.go

@@ -54,6 +54,7 @@ func (m *Manager) initSysfs() {
 		m.sysfsBackend = sysfs
 		m.sysfsReady = true
 		m.updateState()
+		m.initUdev()
 		return
 	}
 
@@ -65,6 +66,11 @@ func (m *Manager) initSysfs() {
 	m.sysfsBackend = sysfs
 	m.sysfsReady = true
 	m.updateState()
+	m.initUdev()
+}
+
+func (m *Manager) initUdev() {
+	m.udevMonitor = NewUdevMonitor(m)
 }
 
 func (m *Manager) initDDC() {

core/internal/server/brightness/types.go

@@ -43,6 +43,7 @@ type Manager struct {
 	logindBackend *LogindBackend
 	sysfsBackend  *SysfsBackend
 	ddcBackend    *DDCBackend
+	udevMonitor   *UdevMonitor
 
 	logindReady bool
 	sysfsReady  bool
@@ -181,6 +182,10 @@ func (m *Manager) Close() {
 		return true
 	})
 
+	if m.udevMonitor != nil {
+		m.udevMonitor.Close()
+	}
+
 	if m.logindBackend != nil {
 		m.logindBackend.Close()
 	}

core/internal/server/brightness/udev.go

@@ -0,0 +1,148 @@
+package brightness
+
+import (
+	"os"
+	"path/filepath"
+	"strconv"
+	"strings"
+
+	"github.com/AvengeMedia/DankMaterialShell/core/internal/log"
+	"github.com/pilebones/go-udev/netlink"
+)
+
+type UdevMonitor struct {
+	stop chan struct{}
+}
+
+func NewUdevMonitor(manager *Manager) *UdevMonitor {
+	m := &UdevMonitor{
+		stop: make(chan struct{}),
+	}
+
+	go m.run(manager)
+	return m
+}
+
+func (m *UdevMonitor) run(manager *Manager) {
+	conn := &netlink.UEventConn{}
+	if err := conn.Connect(netlink.UdevEvent); err != nil {
+		log.Errorf("Failed to connect to udev netlink: %v", err)
+		return
+	}
+	defer conn.Close()
+
+	matcher := &netlink.RuleDefinitions{
+		Rules: []netlink.RuleDefinition{
+			{Env: map[string]string{"SUBSYSTEM": "backlight"}},
+			{Env: map[string]string{"SUBSYSTEM": "leds"}},
+		},
+	}
+	if err := matcher.Compile(); err != nil {
+		log.Errorf("Failed to compile udev matcher: %v", err)
+		return
+	}
+
+	events := make(chan netlink.UEvent)
+	errs := make(chan error)
+	conn.Monitor(events, errs, matcher)
+
+	log.Info("Udev monitor started for backlight/leds events")
+
+	for {
+		select {
+		case <-m.stop:
+			return
+		case err := <-errs:
+			log.Errorf("Udev monitor error: %v", err)
+			return
+		case event := <-events:
+			m.handleEvent(manager, event)
+		}
+	}
+}
+
+func (m *UdevMonitor) handleEvent(manager *Manager, event netlink.UEvent) {
+	subsystem := event.Env["SUBSYSTEM"]
+	devpath := event.Env["DEVPATH"]
+
+	if subsystem == "" || devpath == "" {
+		return
+	}
+
+	sysname := filepath.Base(devpath)
+	action := string(event.Action)
+
+	switch action {
+	case "change":
+		m.handleChange(manager, subsystem, sysname)
+	case "add", "remove":
+		log.Debugf("Udev %s event: %s:%s - triggering rescan", action, subsystem, sysname)
+		manager.Rescan()
+	}
+}
+
+func (m *UdevMonitor) handleChange(manager *Manager, subsystem, sysname string) {
+	deviceID := subsystem + ":" + sysname
+
+	if manager.sysfsBackend == nil {
+		return
+	}
+
+	brightnessPath := filepath.Join(manager.sysfsBackend.basePath, subsystem, sysname, "brightness")
+	data, err := os.ReadFile(brightnessPath)
+	if err != nil {
+		log.Debugf("Udev change event for %s but failed to read brightness: %v", deviceID, err)
+		return
+	}
+
+	brightness, err := strconv.Atoi(strings.TrimSpace(string(data)))
+	if err != nil {
+		log.Debugf("Failed to parse brightness for %s: %v", deviceID, err)
+		return
+	}
+
+	manager.handleUdevBrightnessChange(deviceID, brightness)
+}
+
+func (m *UdevMonitor) Close() {
+	close(m.stop)
+}
+
+func (m *Manager) handleUdevBrightnessChange(deviceID string, rawBrightness int) {
+	if m.sysfsBackend == nil {
+		return
+	}
+
+	dev, err := m.sysfsBackend.GetDevice(deviceID)
+	if err != nil {
+		log.Debugf("Udev event for unknown device %s: %v", deviceID, err)
+		return
+	}
+
+	percent := m.sysfsBackend.ValueToPercent(rawBrightness, dev, false)
+
+	m.stateMutex.Lock()
+	var found bool
+	for i, d := range m.state.Devices {
+		if d.ID != deviceID {
+			continue
+		}
+		found = true
+		if d.Current == rawBrightness {
+			m.stateMutex.Unlock()
+			return
+		}
+		m.state.Devices[i].Current = rawBrightness
+		m.state.Devices[i].CurrentPercent = percent
+		break
+	}
+	m.stateMutex.Unlock()
+
+	if !found {
+		log.Debugf("Udev event for device not in state: %s", deviceID)
+		return
+	}
+
+	log.Debugf("Udev brightness change: %s -> %d (%d%%)", deviceID, rawBrightness, percent)
+	m.broadcastDeviceUpdate(deviceID)
+}

core/internal/server/brightness/udev_test.go

@@ -0,0 +1,260 @@
+package brightness
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+	"time"
+
+	"github.com/pilebones/go-udev/netlink"
+)
+
+func setupTestManager(t *testing.T) (*Manager, string) {
+	tmpDir := t.TempDir()
+
+	backlightDir := filepath.Join(tmpDir, "backlight", "intel_backlight")
+	if err := os.MkdirAll(backlightDir, 0755); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(filepath.Join(backlightDir, "max_brightness"), []byte("1000\n"), 0644); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(filepath.Join(backlightDir, "brightness"), []byte("500\n"), 0644); err != nil {
+		t.Fatal(err)
+	}
+
+	sysfs := &SysfsBackend{
+		basePath: tmpDir,
+		classes:  []string{"backlight"},
+	}
+	if err := sysfs.scanDevices(); err != nil {
+		t.Fatal(err)
+	}
+
+	m := &Manager{
+		sysfsBackend: sysfs,
+		sysfsReady:   true,
+		stopChan:     make(chan struct{}),
+	}
+
+	m.state = State{
+		Devices: []Device{
+			{
+				Class:          ClassBacklight,
+				ID:             "backlight:intel_backlight",
+				Name:           "intel_backlight",
+				Current:        500,
+				Max:            1000,
+				CurrentPercent: 50,
+				Backend:        "sysfs",
+			},
+		},
+	}
+
+	return m, tmpDir
+}
+
+func TestHandleUdevBrightnessChange_UpdatesState(t *testing.T) {
+	m, _ := setupTestManager(t)
+
+	m.handleUdevBrightnessChange("backlight:intel_backlight", 750)
+
+	state := m.GetState()
+	if len(state.Devices) != 1 {
+		t.Fatalf("expected 1 device, got %d", len(state.Devices))
+	}
+
+	dev := state.Devices[0]
+	if dev.Current != 750 {
+		t.Errorf("expected Current=750, got %d", dev.Current)
+	}
+	if dev.CurrentPercent != 75 {
+		t.Errorf("expected CurrentPercent=75, got %d", dev.CurrentPercent)
+	}
+}
+
+func TestHandleUdevBrightnessChange_NoChangeWhenSameValue(t *testing.T) {
+	m, _ := setupTestManager(t)
+
+	updateCh := m.SubscribeUpdates("test")
+	defer m.UnsubscribeUpdates("test")
+
+	m.handleUdevBrightnessChange("backlight:intel_backlight", 500)
+
+	select {
+	case <-updateCh:
+		t.Error("should not broadcast when brightness unchanged")
+	case <-time.After(50 * time.Millisecond):
+	}
+}
+
+func TestHandleUdevBrightnessChange_BroadcastsOnChange(t *testing.T) {
+	m, _ := setupTestManager(t)
+
+	updateCh := m.SubscribeUpdates("test")
+	defer m.UnsubscribeUpdates("test")
+
+	m.handleUdevBrightnessChange("backlight:intel_backlight", 750)
+
+	select {
+	case update := <-updateCh:
+		if update.Device.Current != 750 {
+			t.Errorf("broadcast had wrong Current: got %d, want 750", update.Device.Current)
+		}
+	case <-time.After(100 * time.Millisecond):
+		t.Error("expected broadcast on brightness change")
+	}
+}
+
+func TestHandleUdevBrightnessChange_UnknownDevice(t *testing.T) {
+	m, _ := setupTestManager(t)
+
+	m.handleUdevBrightnessChange("backlight:unknown_device", 500)
+
+	state := m.GetState()
+	if len(state.Devices) != 1 {
+		t.Errorf("state should be unchanged, got %d devices", len(state.Devices))
+	}
+}
+
+func TestHandleUdevBrightnessChange_NilSysfsBackend(t *testing.T) {
+	m := &Manager{
+		sysfsBackend: nil,
+		stopChan:     make(chan struct{}),
+	}
+
+	m.handleUdevBrightnessChange("backlight:test", 500)
+}
+
+func TestHandleUdevBrightnessChange_DeviceNotInState(t *testing.T) {
+	m, _ := setupTestManager(t)
+
+	m.sysfsBackend.deviceCache.Store("backlight:other_device", &sysfsDevice{
+		class:         ClassBacklight,
+		id:            "backlight:other_device",
+		name:          "other_device",
+		maxBrightness: 100,
+		minValue:      1,
+	})
+
+	m.handleUdevBrightnessChange("backlight:other_device", 50)
+
+	state := m.GetState()
+	for _, d := range state.Devices {
+		if d.ID == "backlight:other_device" {
+			t.Error("device should not be added to state via udev change event")
+		}
+	}
+}
+
+func TestHandleEvent_ChangeAction(t *testing.T) {
+	m, tmpDir := setupTestManager(t)
+	um := &UdevMonitor{stop: make(chan struct{})}
+
+	brightnessPath := filepath.Join(tmpDir, "backlight", "intel_backlight", "brightness")
+	if err := os.WriteFile(brightnessPath, []byte("800\n"), 0644); err != nil {
+		t.Fatal(err)
+	}
+
+	event := netlink.UEvent{
+		Action: netlink.CHANGE,
+		Env: map[string]string{
+			"SUBSYSTEM": "backlight",
+			"DEVPATH":   "/devices/pci0000:00/0000:00:02.0/drm/card0/card0-eDP-1/intel_backlight",
+		},
+	}
+
+	um.handleEvent(m, event)
+
+	state := m.GetState()
+	if state.Devices[0].Current != 800 {
+		t.Errorf("expected Current=800 after change event, got %d", state.Devices[0].Current)
+	}
+}
+
+func TestHandleEvent_MissingEnvVars(t *testing.T) {
+	m, _ := setupTestManager(t)
+	um := &UdevMonitor{stop: make(chan struct{})}
+
+	event := netlink.UEvent{
+		Action: netlink.CHANGE,
+		Env:    map[string]string{},
+	}
+
+	um.handleEvent(m, event)
+
+	state := m.GetState()
+	if state.Devices[0].Current != 500 {
+		t.Error("state should be unchanged with missing env vars")
+	}
+}
+
+func TestHandleEvent_MissingSubsystem(t *testing.T) {
+	m, _ := setupTestManager(t)
+	um := &UdevMonitor{stop: make(chan struct{})}
+
+	event := netlink.UEvent{
+		Action: netlink.CHANGE,
+		Env: map[string]string{
+			"DEVPATH": "/devices/foo/bar",
+		},
+	}
+
+	um.handleEvent(m, event)
+
+	state := m.GetState()
+	if state.Devices[0].Current != 500 {
+		t.Error("state should be unchanged with missing SUBSYSTEM")
+	}
+}
+
+func TestHandleChange_BrightnessFileNotFound(t *testing.T) {
+	m, _ := setupTestManager(t)
+	um := &UdevMonitor{stop: make(chan struct{})}
+
+	um.handleChange(m, "backlight", "nonexistent_device")
+
+	state := m.GetState()
+	if state.Devices[0].Current != 500 {
+		t.Error("state should be unchanged when brightness file not found")
+	}
+}
+
+func TestHandleChange_InvalidBrightnessValue(t *testing.T) {
+	m, tmpDir := setupTestManager(t)
+	um := &UdevMonitor{stop: make(chan struct{})}
+
+	brightnessPath := filepath.Join(tmpDir, "backlight", "intel_backlight", "brightness")
+	if err := os.WriteFile(brightnessPath, []byte("not_a_number\n"), 0644); err != nil {
+		t.Fatal(err)
+	}
+
+	um.handleChange(m, "backlight", "intel_backlight")
+
+	state := m.GetState()
+	if state.Devices[0].Current != 500 {
+		t.Error("state should be unchanged with invalid brightness value")
+	}
+}
+
+func TestUdevMonitor_Close(t *testing.T) {
+	um := &UdevMonitor{stop: make(chan struct{})}
+
+	um.Close()
+
+	select {
+	case <-um.stop:
+	default:
+		t.Error("stop channel should be closed")
+	}
+}
+
+func TestHandleChange_NilSysfsBackend(t *testing.T) {
+	m := &Manager{
+		sysfsBackend: nil,
+		stopChan:     make(chan struct{}),
+	}
+	um := &UdevMonitor{stop: make(chan struct{})}
+
+	um.handleChange(m, "backlight", "test_device")
+}