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/histogram.go

@@ -0,0 +1,89 @@
+package tui
+
+import (
+	"fmt"
+	"strings"
+	"time"
+
+	"github.com/charmbracelet/lipgloss"
+)
+
+type latencyBucket struct {
+	label string
+	min   int64
+	max   int64
+	count int
+}
+
+func (m Model) latencyHistogram(latencies []time.Duration, statuses []bool, width int) string {
+	if len(latencies) == 0 || width < 30 {
+		return ""
+	}
+
+	buckets := []latencyBucket{
+		{"0-50ms", 0, 50, 0},
+		{"50-100ms", 50, 100, 0},
+		{"100-200ms", 100, 200, 0},
+		{"200-500ms", 200, 500, 0},
+		{"500ms+", 500, 999999, 0},
+	}
+
+	for i, l := range latencies {
+		if i < len(statuses) && !statuses[i] {
+			continue
+		}
+		ms := l.Milliseconds()
+		for j := range buckets {
+			if ms >= buckets[j].min && ms < buckets[j].max {
+				buckets[j].count++
+				break
+			}
+		}
+	}
+
+	maxCount := 0
+	for _, b := range buckets {
+		if b.count > maxCount {
+			maxCount = b.count
+		}
+	}
+	if maxCount == 0 {
+		return ""
+	}
+
+	labelW := 10
+	countW := len(fmt.Sprintf("%d", maxCount))
+	barW := width - labelW - countW - 4
+	if barW < 5 {
+		barW = 5
+	}
+
+	var sb strings.Builder
+	for _, b := range buckets {
+		fill := 0
+		if maxCount > 0 {
+			fill = b.count * barW / maxCount
+		}
+
+		var barColor lipgloss.Style
+		switch {
+		case b.min < 100:
+			barColor = m.st.specialStyle
+		case b.min < 500:
+			barColor = m.st.warnStyle
+		default:
+			barColor = m.st.dangerStyle
+		}
+
+		bar := barColor.Render(strings.Repeat("█", fill))
+		if fill < barW {
+			bar += m.st.subtleStyle.Render(strings.Repeat("░", barW-fill))
+		}
+
+		label := fmt.Sprintf("%*s", labelW, b.label)
+		count := fmt.Sprintf("%*d", countW, b.count)
+		sb.WriteString("  " + m.st.subtleStyle.Render(label) + " " + bar + " " + count + "\n")
+	}
+
+	return sb.String()
+}

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 {
+		if mw.MonitorID == 0 {
-			return true
+			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 {
+			if s.ParentID == mw.MonitorID {
-				return true
+				set[s.ID] = true
 			}
 		}
 	}
-	return false
+	m.maintSet = set
 }
 
 func (m *Model) initMaintHuhForm() tea.Cmd {

internal/tui/tab_sites.go

@@ -37,7 +37,6 @@ const (
 	colDot colKey = iota
 	colName
 	colType
-	colStatus
 	colLatency
 	colUptime
 	colHistory
@@ -57,15 +56,16 @@ type columnDef struct {
 var siteColumns = []columnDef{
 	{colDot, "", "", 3, 3, 0},
 	{colName, "NAME", "NAME", 0, 0, 0},
-	{colType, "TYPE", "TYPE", 10, 8, mediumBreakpoint},
+	{colType, "TYPE", "TYPE", 10, 8, 0},
-	{colStatus, "STATUS", "STATUS", 10, 10, 0},
 	{colLatency, "LATENCY", "LAT", 10, 7, 0},
-	{colUptime, "UPTIME", "UP%", 8, 8, mediumBreakpoint},
+	{colUptime, "UPTIME", "UP%", 8, 8, 0},
-	{colHistory, "HISTORY", "HISTORY", 0, 0, mediumBreakpoint},
+	{colHistory, "HISTORY", "HISTORY", 0, 0, 0},
-	{colSSL, "SSL", "SSL", 7, 5, wideBreakpoint},
+	{colSSL, "SSL", "SSL", 7, 5, 0},
-	{colRetries, "RETRIES", "RT", 9, 5, wideBreakpoint},
+	{colRetries, "RETRIES", "RT", 9, 5, 0},
 }
 
+var columnDropOrder = []colKey{colHistory, colRetries, colSSL, colUptime, colType}
+
 type tableLayout struct {
 	nameW, sparkW int
 	headers       []string
@@ -76,17 +76,51 @@ type tableLayout struct {
 func (m Model) computeLayout() tableLayout {
 	wide := m.isWide()
 
-	var active []colKey
-	var headers []string
-	var widths []int
-	var fixed int
-
 	cw := m.contentWidth
 	if cw == 0 {
 		cw = m.termWidth
 	}
+
+	dropped := make(map[colKey]bool)
+	minNameW := 20
+	minSparkW := 12
+
+	for attempt := 0; attempt <= len(columnDropOrder); attempt++ {
+		var fixed int
+		var flexCount int
+		for _, c := range siteColumns {
+			if dropped[c.key] {
+				continue
+			}
+			w := c.narrowW
+			if wide {
+				w = c.wideW
+			}
+			if w > 0 {
+				fixed += w
+			} else {
+				flexCount++
+			}
+		}
+		numCols := len(siteColumns) - len(dropped)
+		borderOverhead := 2 + (numCols - 1)
+		avail := cw - chromePadH - 2 - borderOverhead - fixed
+		minFlex := minNameW
+		if flexCount > 1 {
+			minFlex += minSparkW
+		}
+		if avail >= minFlex || attempt >= len(columnDropOrder) {
+			break
+		}
+		dropped[columnDropOrder[attempt]] = true
+	}
+
+	var active []colKey
+	var headers []string
+	var widths []int
+	var fixed int
 	for _, c := range siteColumns {
-		if c.minTerm > 0 && cw < c.minTerm {
+		if dropped[c.key] {
 			continue
 		}
 		active = append(active, c.key)
@@ -106,12 +140,12 @@ func (m Model) computeLayout() tableLayout {
 	}
 
 	sortColMap := map[int]colKey{
-		sortStatus:  colStatus,
+		sortStatus:  colDot,
 		sortName:    colName,
 		sortLatency: colLatency,
 	}
 	sortableKeys := map[colKey]string{
-		colStatus:  "sort-status",
+		colDot:     "sort-status",
 		colName:    "sort-name",
 		colLatency: "sort-latency",
 	}
@@ -250,7 +284,6 @@ func (m Model) viewSitesTab() string {
 						colDot:     m.fmtStatusDot(site.Status, site.Paused, inMaint),
 						colName:    m.zones.Mark(fmt.Sprintf("site-%d", i), icon+" "+limitStr(site.Name, nameW-4)),
 						colType:    "group",
-						colStatus:  m.fmtStatus(site.Status, site.Paused, inMaint),
 						colLatency: m.st.subtleStyle.Render("—"),
 						colUptime:  m.groupUptime(site.ID),
 						colHistory: m.groupSparkline(site.ID, sparkWidth, rowBg),
@@ -299,7 +332,6 @@ func (m Model) viewSitesTab() string {
 					colDot:     m.fmtStatusDot(site.Status, site.Paused, inMaint),
 					colName:    m.zones.Mark(fmt.Sprintf("site-%d", i), name),
 					colType:    typeIcon(site.Type, false) + " " + site.Type,
-					colStatus:  m.fmtStatus(site.Status, site.Paused, inMaint),
 					colLatency: m.fmtLatency(site.Latency),
 					colUptime:  m.fmtUptimeMaint(hist.Statuses, site.ID),
 					colHistory: spark,

internal/tui/tui.go

@@ -119,16 +119,17 @@ const (
 type sessionState int
 
 const (
-	stateDashboard     sessionState = 0
+	stateDashboard        sessionState = 0
-	stateLogs          sessionState = 1
+	stateLogs             sessionState = 1
-	stateAlertDetail   sessionState = 3
+	stateDetailFullscreen sessionState = 2
-	stateFormSite      sessionState = 4
+	stateAlertDetail      sessionState = 3
-	stateFormAlert     sessionState = 5
+	stateFormSite         sessionState = 4
-	stateFormUser      sessionState = 6
+	stateFormAlert        sessionState = 5
-	stateConfirmDelete sessionState = 7
+	stateFormUser         sessionState = 6
-	stateFormMaint     sessionState = 8
+	stateConfirmDelete    sessionState = 7
-	stateSettings      sessionState = 11
+	stateFormMaint        sessionState = 8
-	stateMaintDetail   sessionState = 12
+	stateSettings         sessionState = 11
+	stateMaintDetail      sessionState = 12
 )
 
 type Model struct {
@@ -206,6 +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

@@ -19,7 +19,8 @@ func (m Model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 	case tabDataMsg:
 		return m.handleTabData(msg)
 	case detailDataMsg:
-		if m.detailOpen && m.cursor < len(m.sites) && m.sites[m.cursor].ID != msg.siteID {
+		detailVisible := m.detailOpen || m.state == stateDetailFullscreen
+		if detailVisible && m.cursor < len(m.sites) && m.sites[m.cursor].ID != msg.siteID {
 			return m, nil
 		}
 		m.detailChanges = msg.changes
@@ -51,6 +52,9 @@ func (m Model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 	if m.state == stateLogs {
 		return m.handleLogsFullscreen(msg)
 	}
+	if m.state == stateDetailFullscreen {
+		return m.handleDetailFullscreen(msg)
+	}
 
 	switch msg := msg.(type) {
 	case tea.MouseMsg:
@@ -203,7 +207,7 @@ func (m *Model) handleTick(t time.Time) (tea.Model, tea.Cmd) {
 // tab-data cadence, so a flap that happens while the panel is on screen shows
 // up without leaving and re-entering. Nil when no detail panel is open.
 func (m *Model) detailRefreshCmd() tea.Cmd {
-	if !m.detailOpen || m.cursor >= len(m.sites) {
+	if (!m.detailOpen && m.state != stateDetailFullscreen) || m.cursor >= len(m.sites) {
 		return nil
 	}
 	return m.loadDetailCmd(m.sites[m.cursor].ID)
@@ -227,6 +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
 }
@@ -278,6 +283,75 @@ func (m *Model) handleLogsFullscreen(msg tea.Msg) (tea.Model, tea.Cmd) {
 	return m, nil
 }
 
+func (m *Model) handleDetailFullscreen(msg tea.Msg) (tea.Model, tea.Cmd) {
+	switch msg := msg.(type) {
+	case tea.KeyMsg:
+		switch msg.String() {
+		case "esc", "q":
+			m.state = stateDashboard
+			m.focusedPanel = panelMonitors
+		case "ctrl+c":
+			return m, tea.Quit
+		case "e":
+			return m.handleEditItem()
+		case "h":
+			if m.cursor < len(m.sites) {
+				site := m.sites[m.cursor]
+				m.historySiteName = site.Name
+				m.historySiteID = site.ID
+				m.historyChanges = nil
+				m.detailMode = detailHistory
+				m.detailScrollOffset = 0
+				return m, m.loadHistoryCmd(site.ID)
+			}
+		case "s":
+			if m.cursor < len(m.sites) {
+				site := m.sites[m.cursor]
+				m.slaSiteName = site.Name
+				m.slaSiteID = site.ID
+				m.slaPeriodIdx = 2
+				m.detailMode = detailSLA
+				m.detailScrollOffset = 0
+				return m, m.loadSLACmd(site.ID, m.slaPeriodIdx)
+			}
+		case "1", "2", "3", "4":
+			if m.detailMode == detailSLA {
+				idx := int(msg.String()[0]-'0') - 1
+				if idx >= 0 && idx < len(slaPeriods) {
+					m.slaPeriodIdx = idx
+					m.detailScrollOffset = 0
+					return m, m.loadSLACmd(m.slaSiteID, idx)
+				}
+			}
+		case "up", "k":
+			m.detailScrollOffset--
+			if m.detailScrollOffset < 0 {
+				m.detailScrollOffset = 0
+			}
+		case "down", "j":
+			m.detailScrollOffset++
+		case "pgup":
+			m.detailScrollOffset -= 10
+			if m.detailScrollOffset < 0 {
+				m.detailScrollOffset = 0
+			}
+		case "pgdown":
+			m.detailScrollOffset += 10
+		}
+	case tea.MouseMsg:
+		switch msg.Button {
+		case tea.MouseButtonWheelUp:
+			m.detailScrollOffset -= 3
+			if m.detailScrollOffset < 0 {
+				m.detailScrollOffset = 0
+			}
+		case tea.MouseButtonWheelDown:
+			m.detailScrollOffset += 3
+		}
+	}
+	return m, nil
+}
+
 func (m *Model) handleMouse(msg tea.MouseMsg) (tea.Model, tea.Cmd) {
 	if m.state != stateDashboard {
 		return m, nil
@@ -673,6 +747,13 @@ func (m *Model) handleDashboardKey(msg tea.KeyMsg) (tea.Model, tea.Cmd) {
 			return m, nil
 		}
 		if len(m.sites) > 0 {
+			narrow := m.termWidth < wideBreakpoint
+			if narrow {
+				m.detailMode = detailDefault
+				m.detailScrollOffset = 0
+				m.state = stateDetailFullscreen
+				return m, m.loadDetailCmd(m.sites[m.cursor].ID)
+			}
 			m.detailOpen = !m.detailOpen
 			m.detailMode = detailDefault
 			m.detailScrollOffset = 0

internal/tui/update_test.go

@@ -300,6 +300,70 @@ func TestWriteDoneMsg_LogsErrorAndReloads(t *testing.T) {
 	}
 }
 
+func TestEnterNarrowTerminal_OpensFullscreen(t *testing.T) {
+	ms := &tuiMockStore{stateChanges: []models.StateChange{{FromStatus: "UP", ToStatus: "DOWN"}}}
+	m := newTestModel(ms)
+	m.sites = []models.Site{{SiteConfig: models.SiteConfig{ID: 1, Name: "site"}, SiteState: models.SiteState{Status: "UP"}}}
+	m.termWidth = 80 // narrow, below wideBreakpoint (120)
+	m.termHeight = 40
+	m.focusedPanel = panelMonitors
+
+	updated, cmd := (&m).handleDashboardKey(keyMsg("enter"))
+	got := updated.(*Model)
+	if got.state != stateDetailFullscreen {
+		t.Fatalf("expected stateDetailFullscreen, got %d", got.state)
+	}
+	if cmd == nil {
+		t.Fatal("expected a detail load Cmd")
+	}
+}
+
+func TestEnterWideTerminal_TogglesSidebar(t *testing.T) {
+	ms := &tuiMockStore{stateChanges: []models.StateChange{{FromStatus: "UP", ToStatus: "DOWN"}}}
+	m := newTestModel(ms)
+	m.sites = []models.Site{{SiteConfig: models.SiteConfig{ID: 1, Name: "site"}, SiteState: models.SiteState{Status: "UP"}}}
+	m.termWidth = 140 // wide, above wideBreakpoint (120)
+	m.termHeight = 40
+	m.focusedPanel = panelMonitors
+
+	updated, _ := (&m).handleDashboardKey(keyMsg("enter"))
+	got := updated.(*Model)
+	if got.state != stateDashboard {
+		t.Fatalf("expected stateDashboard, got %d", got.state)
+	}
+	if !got.detailOpen {
+		t.Fatal("expected detailOpen to be true")
+	}
+}
+
+func TestDetailFullscreen_EscReturnsToDashboard(t *testing.T) {
+	m := newTestModel(&tuiMockStore{})
+	m.state = stateDetailFullscreen
+	m.sites = []models.Site{{SiteConfig: models.SiteConfig{ID: 1, Name: "site"}}}
+
+	updated, _ := (&m).handleDetailFullscreen(tea.KeyMsg{Type: tea.KeyEsc})
+	got := updated.(*Model)
+	if got.state != stateDashboard {
+		t.Fatalf("expected stateDashboard after Esc, got %d", got.state)
+	}
+	if got.focusedPanel != panelMonitors {
+		t.Fatalf("expected panelMonitors focus, got %d", got.focusedPanel)
+	}
+}
+
+func TestDetailRefreshCmd_FiresForFullscreen(t *testing.T) {
+	ms := &tuiMockStore{stateChanges: []models.StateChange{{FromStatus: "UP", ToStatus: "DOWN"}}}
+	m := newTestModel(ms)
+	m.sites = []models.Site{{SiteConfig: models.SiteConfig{ID: 5, Name: "site"}}}
+	m.state = stateDetailFullscreen
+	m.detailOpen = false
+
+	cmd := (&m).detailRefreshCmd()
+	if cmd == nil {
+		t.Fatal("detailRefreshCmd should fire for stateDetailFullscreen")
+	}
+}
+
 func TestDetailRefreshCmd_OnlyWhileDetailOpen(t *testing.T) {
 	ms := &tuiMockStore{stateChanges: []models.StateChange{{FromStatus: "UP", ToStatus: "DOWN"}}}
 	m := newTestModel(ms)
@@ -325,3 +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")
+	}
+}

internal/tui/view_dashboard.go

@@ -92,6 +92,8 @@ func (m Model) View() string {
 		return ""
 	case stateLogs:
 		return m.viewLogsFullscreen()
+	case stateDetailFullscreen:
+		return m.viewDetailFullscreen()
 	case stateAlertDetail:
 		return m.viewAlertDetailPanel()
 	case stateSettings:

internal/tui/view_detail_inline.go

@@ -2,6 +2,7 @@ package tui
 
 import (
 	"fmt"
+	"sort"
 	"strings"
 	"time"
 
@@ -22,20 +23,72 @@ func (m Model) viewDetailInline(width, height int) string {
 	default:
 		site := m.sites[m.cursor]
 		hist, _ := m.engine.GetHistory(site.ID)
-		return m.viewDetailSidebar(site, hist, width, height)
+		return m.buildDetailContent(site, hist, width, false)
 	}
 }
 
-func (m Model) viewDetailSidebar(site models.Site, hist monitor.SiteHistory, width, _ int) string {
+func (m Model) viewDetailFullscreen() string {
+	if m.cursor >= len(m.sites) {
+		return ""
+	}
+
+	availW := m.termWidth - chromePadH
+	site := m.sites[m.cursor]
+
+	var title string
+	switch m.detailMode {
+	case detailSLA:
+		title = "SLA · " + site.Name
+	case detailHistory:
+		title = "History · " + site.Name
+	default:
+		title = site.Name
+	}
+
+	if site.ParentID > 0 {
+		for _, s := range m.sites {
+			if s.ID == site.ParentID {
+				title = s.Name + " > " + title
+				break
+			}
+		}
+	}
+
+	innerW := availW - 2
+
+	var content string
+	switch m.detailMode {
+	case detailSLA:
+		content = m.viewSLASidebar(innerW, 0)
+	case detailHistory:
+		content = m.viewHistorySidebar(innerW, 0)
+	default:
+		hist, _ := m.engine.GetHistory(site.ID)
+		content = m.buildDetailContent(site, hist, innerW, true)
+	}
+
+	footer := m.detailFooter(innerW)
+
+	panelH := m.termHeight - chromePadV
+	if panelH < 10 {
+		panelH = 10
+	}
+
+	return lipgloss.NewStyle().Padding(1, 2).Render(
+		m.titledPanelH(title, content, footer, availW, panelH, m.detailScrollOffset, true))
+}
+
+func (m Model) buildDetailContent(site models.Site, hist monitor.SiteHistory, width int, fullscreen bool) string {
 	dot := m.st.subtleStyle.Render(" · ")
 	label := m.st.subtleStyle
-	var b strings.Builder
 	innerW := width - 4
 	if innerW < 20 {
 		innerW = 20
 	}
 
-	// Status + latency + last check
+	var b strings.Builder
+
+	// Status + latency + last check + state since
 	status := m.fmtStatus(site.Status, site.Paused, m.isMonitorInMaintenance(site.ID))
 	statusParts := []string{status}
 	if site.Latency > 0 {
@@ -44,6 +97,10 @@ func (m Model) viewDetailSidebar(site models.Site, hist monitor.SiteHistory, wid
 	if !site.LastCheck.IsZero() {
 		statusParts = append(statusParts, m.fmtTimeAgo(site.LastCheck))
 	}
+	if !site.StatusChangedAt.IsZero() {
+		dur := time.Since(site.StatusChangedAt)
+		statusParts = append(statusParts, label.Render("for")+" "+fmtDuration(dur))
+	}
 	b.WriteString("  " + strings.Join(statusParts, dot) + "\n")
 
 	// Type-specific details
@@ -52,7 +109,10 @@ func (m Model) viewDetailSidebar(site models.Site, hist monitor.SiteHistory, wid
 		b.WriteString("  " + strings.Join(typeParts, dot) + "\n")
 	}
 
-	// Uptime + retries
+	// Extended endpoint fields
+	m.writeEndpointFields(&b, site, label, innerW, fullscreen)
+
+	// Uptime + retries + last success
 	uptimeStr := m.fmtUptime(hist.Statuses)
 	if m.isMonitorInMaintenance(site.ID) {
 		uptimeStr = m.st.subtleStyle.Render("—")
@@ -61,8 +121,21 @@ func (m Model) viewDetailSidebar(site models.Site, hist monitor.SiteHistory, wid
 	if site.Type != "group" && site.MaxRetries > 0 {
 		uptimeParts = append(uptimeParts, label.Render("Retries")+" "+m.fmtRetries(site))
 	}
+	if site.Type != "push" && !site.LastSuccessAt.IsZero() {
+		uptimeParts = append(uptimeParts, label.Render("Last OK")+" "+m.fmtTimeAgo(site.LastSuccessAt))
+	}
 	b.WriteString("  " + strings.Join(uptimeParts, dot) + "\n")
 
+	// Maintenance window name
+	if m.isMonitorInMaintenance(site.ID) {
+		for _, mw := range m.maintenanceWindows {
+			if mw.Type == "maintenance" && (mw.MonitorID == 0 || mw.MonitorID == site.ID || mw.MonitorID == site.ParentID) {
+				b.WriteString("  " + label.Render("Maint") + " " + m.st.maintStyle.Render(mw.Title) + "\n")
+				break
+			}
+		}
+	}
+
 	// Error line
 	if (site.Status == models.StatusDown || site.Status == models.StatusSSLExp ||
 		site.Status == models.StatusLate || site.Status == models.StatusStale) && site.LastError != "" {
@@ -73,8 +146,62 @@ func (m Model) viewDetailSidebar(site models.Site, hist monitor.SiteHistory, wid
 		b.WriteString("  " + label.Render("Error") + " " + m.st.dangerStyle.Render(limitStr(site.LastError, errW)) + "\n")
 	}
 
+	// Connection chain
+	if (site.Status == models.StatusDown || site.Status == models.StatusSSLExp) && site.LastError != "" {
+		chain := connectionChain(site.LastError, site.Type, site.StatusCode, strings.HasPrefix(site.URL, "https"))
+		if len(chain) > 0 {
+			b.WriteString("\n")
+			for _, step := range chain {
+				var icon string
+				switch step.Status {
+				case stepPassed:
+					icon = m.st.specialStyle.Render("✓")
+				case stepFailed:
+					icon = m.st.dangerStyle.Render("✗")
+				case stepSkipped:
+					icon = m.st.subtleStyle.Render("·")
+				}
+				line := fmt.Sprintf("  %s %-16s", icon, step.Name)
+				if step.Detail != "" {
+					switch step.Status {
+					case stepFailed:
+						line += " " + m.st.dangerStyle.Render(step.Detail)
+					case stepSkipped:
+						line += " " + m.st.subtleStyle.Render(step.Detail)
+					}
+				}
+				b.WriteString(line + "\n")
+			}
+		}
+	}
+
 	b.WriteString("\n")
 
+	// Probe results
+	probeResults := m.engine.GetProbeResults(site.ID)
+	if len(probeResults) > 0 {
+		nodeIDs := make([]string, 0, len(probeResults))
+		for id := range probeResults {
+			nodeIDs = append(nodeIDs, id)
+		}
+		sort.Strings(nodeIDs)
+		for _, nodeID := range nodeIDs {
+			result := probeResults[nodeID]
+			probeStatus := m.st.specialStyle.Render("UP")
+			if !result.IsUp {
+				probeStatus = m.st.dangerStyle.Render("DN")
+			}
+			latency := time.Duration(result.LatencyNs).Milliseconds()
+			ago := time.Since(result.CheckedAt).Truncate(time.Second)
+			line := fmt.Sprintf("  %-14s %s  %dms  %s ago", nodeID, probeStatus, latency, ago)
+			if !result.IsUp && result.ErrorReason != "" {
+				line += "  " + m.st.dangerStyle.Render(result.ErrorReason)
+			}
+			b.WriteString(line + "\n")
+		}
+		b.WriteString("\n")
+	}
+
 	// Latency chart
 	if len(hist.Latencies) > 0 {
 		chart := m.latencyChart(hist.Latencies, hist.Statuses, innerW, 3)
@@ -116,6 +243,15 @@ func (m Model) viewDetailSidebar(site models.Site, hist monitor.SiteHistory, wid
 		}
 	}
 
+	// Latency histogram
+	if site.Type != "push" && len(hist.Latencies) > 5 {
+		histContent := m.latencyHistogram(hist.Latencies, hist.Statuses, innerW)
+		if histContent != "" {
+			b.WriteString("\n")
+			b.WriteString(histContent)
+		}
+	}
+
 	b.WriteString("\n")
 
 	// State changes
@@ -150,6 +286,47 @@ func (m Model) viewDetailSidebar(site models.Site, hist monitor.SiteHistory, wid
 	return lipgloss.NewStyle().Width(width).MaxWidth(width).Render(b.String())
 }
 
+func (m Model) writeEndpointFields(b *strings.Builder, site models.Site, label lipgloss.Style, innerW int, fullscreen bool) {
+	dot := m.st.subtleStyle.Render(" · ")
+	var fields []string
+
+	if site.Interval > 0 {
+		fields = append(fields, label.Render("Every")+" "+fmt.Sprintf("%ds", site.Interval))
+	}
+	if site.Timeout > 0 {
+		fields = append(fields, label.Render("Timeout")+" "+fmt.Sprintf("%ds", site.Timeout))
+	}
+	if site.Type == "http" && site.Method != "" && site.Method != "GET" {
+		fields = append(fields, label.Render("Method")+" "+site.Method)
+	}
+	if site.Type == "http" {
+		codes := site.AcceptedCodes
+		if codes == "" {
+			codes = "200-299"
+		}
+		fields = append(fields, label.Render("Codes")+" "+codes)
+	}
+	if site.Regions != "" {
+		fields = append(fields, label.Render("Regions")+" "+site.Regions)
+	}
+
+	if len(fields) > 0 {
+		b.WriteString("  " + strings.Join(fields, dot) + "\n")
+	}
+
+	if site.Description != "" {
+		maxDescW := innerW
+		if !fullscreen && maxDescW > 60 {
+			maxDescW = 60
+		}
+		b.WriteString("  " + label.Render(limitStr(site.Description, maxDescW)) + "\n")
+	}
+
+	if site.Type == "push" && site.Token != "" {
+		b.WriteString("  " + label.Render("Token") + " " + site.Token + "\n")
+	}
+}
+
 func (m Model) detailTypeLine(site models.Site) []string {
 	label := m.st.subtleStyle
 	var parts []string