fix: keep server list usable with many servers

docs/superpowers/plans/2026-05-28-server-list-scalability.md

@@ -15,7 +15,7 @@
 **Files:**
 - Modify: `internal/tui/app_test.go`
 
-- [ ] **Step 1: Add a test for a constrained terminal height**
+- [x] **Step 1: Add a test for a constrained terminal height**
 
 Add a test that creates more servers than can fit on screen, sets a small terminal size, renders the list, and verifies the selected details and footer are still visible.
 
@@ -54,7 +54,7 @@ func TestServerListViewKeepsDetailsVisibleWithManyServers(t *testing.T) {
 }
 ```
 
-- [ ] **Step 2: Run the focused test and confirm it fails**
+- [x] **Step 2: Run the focused test and confirm it fails**
 
 Run:
 
@@ -70,7 +70,7 @@ Expected: FAIL because the current table renders every server and can push the d
 - Modify: `internal/tui/app.go`
 - Modify: `internal/tui/app_test.go`
 
-- [ ] **Step 1: Add focused tests for visible range calculation**
+- [x] **Step 1: Add focused tests for visible range calculation**
 
 Add tests for a helper that computes the inclusive start and exclusive end indexes for rendered rows.
 
@@ -101,7 +101,7 @@ func TestVisibleServerRangeKeepsSelectionInsideWindow(t *testing.T) {
 }
 ```
 
-- [ ] **Step 2: Implement `visibleServerRange`**
+- [x] **Step 2: Implement `visibleServerRange`**
 
 Add a small helper near `selectedServer`.
 
@@ -133,7 +133,7 @@ func visibleServerRange(total, selected, available int) (int, int) {
 }
 ```
 
-- [ ] **Step 3: Run helper tests**
+- [x] **Step 3: Run helper tests**
 
 Run:
 
@@ -149,7 +149,7 @@ Expected: PASS.
 - Modify: `internal/tui/app.go`
 - Modify: `internal/tui/app_test.go`
 
-- [ ] **Step 1: Reserve terminal space for fixed UI blocks**
+- [x] **Step 1: Reserve terminal space for fixed UI blocks**
 
 Add a helper that decides how many server rows may be rendered while keeping the selected details and footer visible.
 
@@ -168,7 +168,7 @@ func (m *tuiModel) visibleServerRows() int {
 }
 ```
 
-- [ ] **Step 2: Use the visible range in `viewServerList`**
+- [x] **Step 2: Use the visible range in `viewServerList`**
 
 In `viewServerList`, replace the loop over all servers with a bounded loop:
 
@@ -189,7 +189,7 @@ if len(m.servers) > end-start {
 }
 ```
 
-- [ ] **Step 3: Run long-list regression test**
+- [x] **Step 3: Run long-list regression test**
 
 Run:
 
@@ -204,7 +204,7 @@ Expected: PASS.
 **Files:**
 - Modify: `internal/tui/app_test.go`
 
-- [ ] **Step 1: Add a test for moving selection beyond the first window**
+- [x] **Step 1: Add a test for moving selection beyond the first window**
 
 Use the existing `m.list.Update` path by sending `tea.KeyDown` messages and confirm the rendered window follows the selected server.
 
@@ -240,7 +240,7 @@ func TestServerListViewScrollsWithSelection(t *testing.T) {
 }
 ```
 
-- [ ] **Step 2: Run TUI tests**
+- [x] **Step 2: Run TUI tests**
 
 Run:
 
@@ -255,7 +255,7 @@ Expected: PASS.
 **Files:**
 - No source edits expected.
 
-- [ ] **Step 1: Run the full test suite**
+- [x] **Step 1: Run the full test suite**
 
 Run:
 
@@ -265,7 +265,7 @@ env GOCACHE=/tmp/sshkeeper-go-cache go test ./...
 
 Expected: all packages pass.
 
-- [ ] **Step 2: Rebuild the project binary**
+- [x] **Step 2: Rebuild the project binary**
 
 Run:
 
@@ -275,7 +275,7 @@ env GOCACHE=/tmp/sshkeeper-go-cache go build -o bin/sshkeeper .
 
 Expected: exit code 0 and updated `bin/sshkeeper`.
 
-- [ ] **Step 3: Commit the implementation**
+- [x] **Step 3: Commit the implementation**
 
 Run:
 

internal/tui/app.go

@@ -417,7 +417,9 @@ func (m *tuiModel) viewServerList() string {
 		b.WriteString(helpStyle.Render("  No servers yet. Press Ctrl+A to add one."))
 		b.WriteString("\n")
 	} else {
-		for _, server := range m.servers {
+		selectedIndex := m.list.Index()
+		start, end := visibleServerRange(len(m.servers), selectedIndex, m.visibleServerRows())
+		for _, server := range m.servers[start:end] {
 			marker := " "
 			rowStyle := normalStyle
 			if server.Alias == selectedAlias {
@@ -445,6 +447,10 @@ func (m *tuiModel) viewServerList() string {
 			b.WriteString(rowStyle.Render(row))
 			b.WriteString("\n")
 		}
+		if len(m.servers) > end-start {
+			b.WriteString(helpStyle.Render(fmt.Sprintf("  Showing %d-%d of %d", start+1, end, len(m.servers))))
+			b.WriteString("\n")
+		}
 	}
 
 	b.WriteString("\n")
@@ -465,6 +471,45 @@ func (m *tuiModel) selectedServer() *model.Server {
 	return nil
 }
 
+func (m *tuiModel) visibleServerRows() int {
+	if m.height <= 0 {
+		return len(m.servers)
+	}
+
+	const fixedRows = 16
+	rows := m.height - fixedRows
+	if rows < 3 {
+		return 3
+	}
+	return rows
+}
+
+func visibleServerRange(total, selected, available int) (int, int) {
+	if total <= 0 || available <= 0 {
+		return 0, 0
+	}
+	if available >= total {
+		return 0, total
+	}
+	if selected < 0 {
+		selected = 0
+	}
+	if selected >= total {
+		selected = total - 1
+	}
+
+	start := selected - available + 1
+	if start < 0 {
+		start = 0
+	}
+	end := start + available
+	if end > total {
+		end = total
+		start = end - available
+	}
+	return start, end
+}
+
 func (m *tuiModel) viewSelectedServer(server *model.Server) string {
 	displayName := server.DisplayName
 	if displayName == "" {

internal/tui/app_test.go

@@ -1,6 +1,7 @@
 package tui
 
 import (
+	"fmt"
 	"strings"
 	"testing"
 	"time"
@@ -68,6 +69,94 @@ func TestServerListViewUsesDashboardLayout(t *testing.T) {
 	}
 }
 
+func TestServerListViewKeepsDetailsVisibleWithManyServers(t *testing.T) {
+	servers := make([]*model.Server, 45)
+	for i := range servers {
+		servers[i] = &model.Server{
+			Alias:          fmt.Sprintf("server-%02d", i+1),
+			DisplayName:    fmt.Sprintf("Server %02d", i+1),
+			Host:           fmt.Sprintf("host-%02d.example.org", i+1),
+			Port:           22,
+			User:           "mirivlad",
+			AuthMethod:     model.AuthKey,
+			LastTestStatus: model.TestUnknown,
+		}
+	}
+
+	m := New(servers)
+	updated, _ := m.Update(tea.WindowSizeMsg{Width: 100, Height: 18})
+	model := updated.(*tuiModel)
+
+	view := model.View()
+	if !strings.Contains(view, "Server 01") {
+		t.Fatalf("expected first selected server to be visible:\n%s", view)
+	}
+	if !strings.Contains(view, "Selected") {
+		t.Fatalf("expected selected server details to remain visible:\n%s", view)
+	}
+	if !strings.Contains(view, "Enter connect") {
+		t.Fatalf("expected footer to remain visible:\n%s", view)
+	}
+	if count := strings.Count(view, "server-"); count >= len(servers) {
+		t.Fatalf("expected bounded row rendering, rendered %d server aliases", count)
+	}
+}
+
+func TestVisibleServerRangeKeepsSelectionInsideWindow(t *testing.T) {
+	tests := []struct {
+		name      string
+		total     int
+		selected  int
+		available int
+		wantStart int
+		wantEnd   int
+	}{
+		{name: "first page", total: 40, selected: 0, available: 10, wantStart: 0, wantEnd: 10},
+		{name: "middle page", total: 40, selected: 20, available: 10, wantStart: 11, wantEnd: 21},
+		{name: "last page", total: 40, selected: 39, available: 10, wantStart: 30, wantEnd: 40},
+		{name: "all fit", total: 5, selected: 3, available: 10, wantStart: 0, wantEnd: 5},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			start, end := visibleServerRange(tt.total, tt.selected, tt.available)
+			if start != tt.wantStart || end != tt.wantEnd {
+				t.Fatalf("visibleServerRange() = %d, %d; want %d, %d", start, end, tt.wantStart, tt.wantEnd)
+			}
+		})
+	}
+}
+
+func TestServerListViewScrollsWithSelection(t *testing.T) {
+	servers := make([]*model.Server, 45)
+	for i := range servers {
+		servers[i] = &model.Server{
+			Alias:       fmt.Sprintf("server-%02d", i+1),
+			DisplayName: fmt.Sprintf("Server %02d", i+1),
+			Host:        fmt.Sprintf("host-%02d.example.org", i+1),
+			Port:        22,
+			User:        "mirivlad",
+			AuthMethod:  model.AuthKey,
+		}
+	}
+
+	m := New(servers)
+	updated, _ := m.Update(tea.WindowSizeMsg{Width: 100, Height: 18})
+	model := updated.(*tuiModel)
+	for i := 0; i < 20; i++ {
+		updated, _ = model.Update(tea.KeyMsg{Type: tea.KeyDown})
+		model = updated.(*tuiModel)
+	}
+
+	view := model.View()
+	if !strings.Contains(view, "Server 21") {
+		t.Fatalf("expected selected server to be visible after navigation:\n%s", view)
+	}
+	if !strings.Contains(view, "Showing") {
+		t.Fatalf("expected range hint for long server list:\n%s", view)
+	}
+}
+
 func TestEscClosesGroupListBeforeLeavingForm(t *testing.T) {
 	oldGetGroups := GetGroups
 	GetGroups = func() ([]string, error) {