feat(tui): fullscreen detail view + enriched sidebar content

On narrow terminals (<120 cols), Enter opens a fullscreen detail view
instead of the sidebar that can't be seen. Wide terminals keep existing
sidebar toggle behavior.

Enrich detail panel with: state since, last success, connection chain
diagnostic, probe results, latency histogram, extended endpoint fields
(interval/timeout/method/codes/regions/description), push token,
maintenance window name. Breadcrumb shown in fullscreen mode only.

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/tui.go

@@ -121,6 +121,7 @@ type sessionState int
 const (
 	stateDashboard        sessionState = 0
 	stateLogs             sessionState = 1
+	stateDetailFullscreen sessionState = 2
 	stateAlertDetail      sessionState = 3
 	stateFormSite         sessionState = 4
 	stateFormAlert        sessionState = 5

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)
@@ -278,6 +282,75 @@ 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 +746,13 @@ 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)

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 +23,90 @@ 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 ""
+	}
+
+	totalW := 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
+	}
+
+	var breadcrumb string
+	if site.ParentID > 0 {
+		for _, s := range m.sites {
+			if s.ID == site.ParentID {
+				breadcrumb = m.st.subtleStyle.Render("Monitors > "+s.Name+" > ") + m.st.titleStyle.Render(site.Name)
+				break
+			}
+		}
+	}
+	if breadcrumb == "" {
+		breadcrumb = m.st.subtleStyle.Render("Monitors > ") + m.st.titleStyle.Render(title)
+	}
+
+	header := "  " + breadcrumb + "\n" + m.divider()
+
+	var content string
+	switch m.detailMode {
+	case detailSLA:
+		content = m.viewSLASidebar(totalW, 0)
+	case detailHistory:
+		content = m.viewHistorySidebar(totalW, 0)
+	default:
+		hist, _ := m.engine.GetHistory(site.ID)
+		content = m.buildDetailContent(site, hist, totalW, true)
+	}
+
+	footer := m.divider() + "\n" + m.detailFooter(totalW)
+
+	contentLines := strings.Split(content, "\n")
+	contentH := m.termHeight - 8
+	if contentH < 5 {
+		contentH = 5
+	}
+
+	if m.detailScrollOffset > len(contentLines)-contentH {
+		m.detailScrollOffset = len(contentLines) - contentH
+	}
+	if m.detailScrollOffset < 0 {
+		m.detailScrollOffset = 0
+	}
+
+	end := m.detailScrollOffset + contentH
+	if end > len(contentLines) {
+		end = len(contentLines)
+	}
+	visible := strings.Join(contentLines[m.detailScrollOffset:end], "\n")
+
+	return lipgloss.NewStyle().Padding(1, 2).Render(
+		header + "\n" + visible + "\n" + footer)
+}
+
+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 +115,10 @@ 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 +127,10 @@ 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 +139,21 @@ 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 != "" {
@@ -73,7 +164,61 @@ 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 {
@@ -116,6 +261,15 @@ 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 +304,47 @@ 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