perf(tui): precompute maintenance set, eliminate redundant GetAllSites

Replace O(windows × sites) isMonitorInMaintenance with O(1) map lookup.
buildMaintSet runs once per refreshLive/handleTabData, not per call site.

groupSparkline/groupUptime now use m.sites (already on model) instead of
calling engine.GetAllSites() which copies the full map under a mutex.

internal/tui/data.go

@@ -123,6 +123,7 @@ func (m *Model) refreshLive() {
 		ordered = filterSites(ordered, m.filterText)
 	}
 	m.sites = ordered
+	m.buildMaintSet()
 	m.refreshLogContent()
 
 	if m.selectedID != 0 {

internal/tui/sparkline.go

@@ -156,9 +156,8 @@ func resolveSparklineIndex(x, sparkWidth, dataLen int) int {
 }
 
 func (m Model) groupSparkline(groupID int, width int, bg lipgloss.TerminalColor) string {
-	allSites := m.engine.GetAllSites()
 	var childStatuses [][]bool
-	for _, s := range allSites {
+	for _, s := range m.sites {
 		if s.ParentID == groupID && !s.Paused && !m.isMonitorInMaintenance(s.ID) {
 			hist, _ := m.engine.GetHistory(s.ID)
 			if len(hist.Statuses) > 0 {
@@ -209,9 +208,8 @@ func (m Model) groupSparkline(groupID int, width int, bg lipgloss.TerminalColor)
 }
 
 func (m Model) groupUptime(groupID int) string {
-	allSites := m.engine.GetAllSites()
 	var allStatuses [][]bool
-	for _, s := range allSites {
+	for _, s := range m.sites {
 		if s.ParentID == groupID && !s.Paused && !m.isMonitorInMaintenance(s.ID) {
 			hist, _ := m.engine.GetHistory(s.ID)
 			if len(hist.Statuses) > 0 {

internal/tui/tab_maint.go

@@ -21,27 +21,36 @@ type maintFormData struct {
 }
 
 func (m Model) isMonitorInMaintenance(monitorID int) bool {
+	return m.maintSet[monitorID]
+}
+
+func (m *Model) buildMaintSet() {
+	set := make(map[int]bool)
+	now := time.Now()
 	for _, mw := range m.maintenanceWindows {
 		if mw.Type != "maintenance" {
 			continue
 		}
-		now := time.Now()
 		if mw.StartTime.After(now) {
 			continue
 		}
 		if !mw.EndTime.IsZero() && mw.EndTime.Before(now) {
 			continue
 		}
-		if mw.MonitorID == 0 || mw.MonitorID == monitorID {
-			return true
+		if mw.MonitorID == 0 {
+			for _, s := range m.sites {
+				set[s.ID] = true
+			}
+			break
 		}
+		set[mw.MonitorID] = true
 		for _, s := range m.sites {
-			if s.ID == monitorID && s.ParentID > 0 && mw.MonitorID == s.ParentID {
-				return true
+			if s.ParentID == mw.MonitorID {
+				set[s.ID] = true
 			}
 		}
 	}
-	return false
+	m.maintSet = set
 }
 
 func (m *Model) initMaintHuhForm() tea.Cmd {

internal/tui/tui.go

@@ -207,6 +207,7 @@ type Model struct {
 	lastTabLoad        time.Time // last dispatch of loadTabDataCmd (throttle)
 	tabSeq             int       // seq of the newest issued tab-data load
 
+	maintSet            map[int]bool
 	bottomPanel         bottomPanel
 	detailOpen          bool
 	maintCursor         int

internal/tui/update.go

@@ -231,6 +231,7 @@ func (m *Model) handleTabData(msg tabDataMsg) (tea.Model, tea.Cmd) {
 	}
 	m.nodes = msg.nodes
 	m.maintenanceWindows = msg.maint
+	m.buildMaintSet()
 	m.clampCursor()
 	return m, nil
 }

internal/tui/update_test.go

@@ -389,3 +389,86 @@ func TestDetailRefreshCmd_OnlyWhileDetailOpen(t *testing.T) {
 		t.Error("refresh Cmd issued for an out-of-range cursor")
 	}
 }
+
+func TestBuildMaintSet_GlobalWindow(t *testing.T) {
+	m := newTestModel(&tuiMockStore{})
+	m.sites = []models.Site{
+		{SiteConfig: models.SiteConfig{ID: 1, Name: "a"}},
+		{SiteConfig: models.SiteConfig{ID: 2, Name: "b"}},
+	}
+	m.maintenanceWindows = []models.MaintenanceWindow{
+		{ID: 1, MonitorID: 0, Type: "maintenance", StartTime: time.Now().Add(-time.Hour)},
+	}
+	m.buildMaintSet()
+	if !m.maintSet[1] || !m.maintSet[2] {
+		t.Error("global maint window should mark all monitors")
+	}
+}
+
+func TestBuildMaintSet_TargetedWindow(t *testing.T) {
+	m := newTestModel(&tuiMockStore{})
+	m.sites = []models.Site{
+		{SiteConfig: models.SiteConfig{ID: 1, Name: "a"}},
+		{SiteConfig: models.SiteConfig{ID: 2, Name: "b"}},
+	}
+	m.maintenanceWindows = []models.MaintenanceWindow{
+		{ID: 1, MonitorID: 1, Type: "maintenance", StartTime: time.Now().Add(-time.Hour)},
+	}
+	m.buildMaintSet()
+	if !m.maintSet[1] {
+		t.Error("targeted window should mark monitor 1")
+	}
+	if m.maintSet[2] {
+		t.Error("targeted window should NOT mark monitor 2")
+	}
+}
+
+func TestBuildMaintSet_GroupPropagates(t *testing.T) {
+	m := newTestModel(&tuiMockStore{})
+	m.sites = []models.Site{
+		{SiteConfig: models.SiteConfig{ID: 10, Name: "group", Type: "group"}},
+		{SiteConfig: models.SiteConfig{ID: 11, Name: "child1", ParentID: 10}},
+		{SiteConfig: models.SiteConfig{ID: 12, Name: "child2", ParentID: 10}},
+		{SiteConfig: models.SiteConfig{ID: 20, Name: "other"}},
+	}
+	m.maintenanceWindows = []models.MaintenanceWindow{
+		{ID: 1, MonitorID: 10, Type: "maintenance", StartTime: time.Now().Add(-time.Hour)},
+	}
+	m.buildMaintSet()
+	if !m.maintSet[10] || !m.maintSet[11] || !m.maintSet[12] {
+		t.Error("group maint window should mark group + children")
+	}
+	if m.maintSet[20] {
+		t.Error("unrelated monitor should NOT be marked")
+	}
+}
+
+func TestBuildMaintSet_ExpiredIgnored(t *testing.T) {
+	m := newTestModel(&tuiMockStore{})
+	m.sites = []models.Site{
+		{SiteConfig: models.SiteConfig{ID: 1, Name: "a"}},
+	}
+	m.maintenanceWindows = []models.MaintenanceWindow{
+		{ID: 1, MonitorID: 1, Type: "maintenance",
+			StartTime: time.Now().Add(-2 * time.Hour),
+			EndTime:   time.Now().Add(-1 * time.Hour)},
+	}
+	m.buildMaintSet()
+	if m.maintSet[1] {
+		t.Error("expired maint window should not mark monitor")
+	}
+}
+
+func TestBuildMaintSet_IncidentIgnored(t *testing.T) {
+	m := newTestModel(&tuiMockStore{})
+	m.sites = []models.Site{
+		{SiteConfig: models.SiteConfig{ID: 1, Name: "a"}},
+	}
+	m.maintenanceWindows = []models.MaintenanceWindow{
+		{ID: 1, MonitorID: 0, Type: "incident", StartTime: time.Now().Add(-time.Hour)},
+	}
+	m.buildMaintSet()
+	if m.maintSet[1] {
+		t.Error("incident windows should not mark monitors as in maintenance")
+	}
+}