feat(ui): add vertical volume bar to playback view

Add Volume() to Player interface and mpvPlayer implementation to
expose current volume level. Poll volume periodically and render a
vertical bar next to the metadata display during playback. Update
UI state and tests to support the new volume indicator.

internal/player/player.go

@@ -37,6 +37,9 @@ type Player interface {
 	// Volume controls (relative, best effort; mpv uses "add volume ±5" etc.)
 	VolumeUp() error
 	VolumeDown() error
+
+	// Volume returns current volume level (0-100).
+	Volume() int
 }
 
 // IsInstalled reports whether the named executable is on PATH.
@@ -102,6 +105,7 @@ func (p *legacyPlayer) Next() error      { return nil }
 func (p *legacyPlayer) Prev() error      { return nil }
 func (p *legacyPlayer) VolumeUp() error   { return nil }
 func (p *legacyPlayer) VolumeDown() error { return nil }
+func (p *legacyPlayer) Volume() int        { return 70 }
 
 // isShellMeta reports if name looks like it contains shell metachars (defense in depth).
 func isShellMeta(name string) bool {
@@ -145,6 +149,7 @@ type mpvPlayer struct {
 	title  string
 	paused bool
 	muted  bool
+	vol    int
 }
 
 func (p *mpvPlayer) Play(url string, extra ...string) error {
@@ -190,6 +195,9 @@ func (p *mpvPlayer) Play(url string, extra ...string) error {
 	p.send(map[string]any{"command": []any{"observe_property", 2, "metadata"}})
 	p.send(map[string]any{"command": []any{"observe_property", 3, "pause"}})
 	p.send(map[string]any{"command": []any{"observe_property", 4, "mute"}})
+	p.send(map[string]any{"command": []any{"observe_property", 5, "volume"}})
+	// get initial volume
+	p.send(map[string]any{"command": []any{"get_property", "volume"}})
 
 	go p.readLoop()
 	return nil
@@ -210,9 +218,7 @@ func (p *mpvPlayer) readLoop() {
 		if json.Unmarshal(sc.Bytes(), &msg) != nil {
 			continue
 		}
-		if msg["event"] != "property-change" {
-			continue
-		}
+		if msg["event"] == "property-change" {
 			id, _ := msg["id"].(float64)
 			data := msg["data"]
 			p.mu.Lock()
@@ -237,8 +243,24 @@ func (p *mpvPlayer) readLoop() {
 				if b, ok := data.(bool); ok {
 					p.muted = b
 				}
+			case 5:
+				if f, ok := data.(float64); ok {
+					p.vol = int(f + 0.5)
+				}
 			}
 			p.mu.Unlock()
+			continue
+		}
+		// handle get_property response for initial volume
+		if data, ok := msg["data"]; ok {
+			if f, ok := data.(float64); ok {
+				if req, _ := msg["request_id"].(float64); req == 0 { // rough
+					p.mu.Lock()
+					p.vol = int(f + 0.5)
+					p.mu.Unlock()
+				}
+			}
+		}
 	}
 }
 
@@ -300,6 +322,12 @@ func (p *mpvPlayer) VolumeDown() error {
 	return nil
 }
 
+func (p *mpvPlayer) Volume() int {
+	p.mu.Lock()
+	defer p.mu.Unlock()
+	return p.vol
+}
+
 func (p *mpvPlayer) Stop() error {
 	if p.conn != nil {
 		p.send(map[string]any{"command": []any{"quit"}})

internal/player/player_test.go

@@ -36,6 +36,7 @@ func TestMpvInterfaceAndControls(t *testing.T) {
 	_ = p.Prev()
 	_ = p.VolumeUp()
 	_ = p.VolumeDown()
+	_ = p.Volume()
 	if p.Metadata() != "" {
 		t.Log("mpv metadata (may be empty for echo stub)")
 	}

internal/ui/ui.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"io"
 	"log"
+	"math"
 	"strings"
 	"time"
 
@@ -98,6 +99,7 @@ type App struct {
 	nowPlaying    string // streamed metadata title
 	paused        bool
 	muted         bool
+	currentVolume int
 }
 
 func NewApp(initial []radio.Station) *App {
@@ -291,13 +293,20 @@ func (a *App) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 				a.nowPlaying = i.station.Name
 				a.paused = false
 				a.muted = false
+				a.currentVolume = 70 // default, will be updated by poll/observe
 				if a.player != nil {
+					if v := a.player.Volume(); v > 0 {
+						a.currentVolume = v
+					}
 					// launch in goroutine so TUI doesn't block even if using legacy player
 					// (for mpv+IPC this returns immediately anyway)
 					go func() { _ = a.player.Play(i.station.Url) }()
 				}
-				// start polling for streamed metadata (works for both legacy stub + real mpv ipc)
-				return a, metadataPollCmd(a.player)
+				// start polling for streamed metadata and volume (for the vertical bar)
+				return a, tea.Batch(
+					metadataPollCmd(a.player),
+					volumePollCmd(a.player),
+				)
 			}
 			return a, nil
 		case "f":
@@ -365,6 +374,14 @@ func (a *App) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 			return a, metadataPollCmd(a.player)
 		}
 		return a, nil
+	case volumeMsg:
+		if a.playing {
+			a.currentVolume = msg.volume
+		}
+		if a.playing && a.player != nil {
+			return a, volumePollCmd(a.player)
+		}
+		return a, nil
 	case searchResultsMsg:
 		if msg.err != nil {
 			a.list.Title = fmt.Sprintf("Search error: %v (press / to search again)", msg.err)
@@ -463,7 +480,7 @@ func (a *App) renderPlayback() string {
 		Padding(1, 2).
 		Width(boxW)
 
-	dispW := min(boxW-6, 58)
+	dispW := min(boxW-10, 50) // leave room for vertical vol bar (~2) + separator
 	display := lipgloss.NewStyle().
 		Background(lipgloss.Color("235")).
 		Foreground(lipgloss.Color("46")). // classic green lcd
@@ -472,20 +489,26 @@ func (a *App) renderPlayback() string {
 		Padding(1, 1).
 		Align(lipgloss.Left)
 
-	// build the "screen" text
-	lines := []string{
+	// build the metadata content
+	metaLines := []string{
 		lipgloss.NewStyle().Bold(true).Render("NOW PLAYING"),
 		"",
 		truncate(a.playingItem.station.Name, dispW-2),
 	}
 	if a.nowPlaying != "" {
-		lines = append(lines, truncate(a.nowPlaying, dispW-2))
+		metaLines = append(metaLines, truncate(a.nowPlaying, dispW-2))
 	} else {
-		lines = append(lines, "(waiting for stream metadata...)")
+		metaLines = append(metaLines, "(waiting for stream metadata...)")
 	}
-	lines = append(lines, truncate(a.playingItem.station.Url, dispW-4))
+	metaLines = append(metaLines, truncate(a.playingItem.station.Url, dispW-4))
 
-	screen := display.Render(strings.Join(lines, "\n"))
+	metadata := display.Render(strings.Join(metaLines, "\n"))
+
+	// vertical volume bar to the right of the metadata display
+	volBar := renderVolumeBar(a.currentVolume, 5, 2)
+
+	// place side-by-side (top aligned). Add a small separator space.
+	viewer := lipgloss.JoinHorizontal(lipgloss.Top, metadata, " ", volBar)
 
 	// button row (text buttons, stateful)
 	playBtn := "[ > ]"
@@ -504,7 +527,7 @@ func (a *App) renderPlayback() string {
 	inner := lipgloss.JoinVertical(lipgloss.Left,
 		lipgloss.NewStyle().Bold(true).Foreground(lipgloss.Color("63")).Render("GoStations"),
 		"",
-		screen,
+		viewer,
 		"",
 		btnRow,
 		help,
@@ -520,6 +543,47 @@ func min(a, b int) int {
 	return b
 }
 
+// renderVolumeBar draws a vertical volume indicator bar.
+// height matches the metadata display (e.g. 5).
+// background is dark gray ("236"), filled indicator uses the green ("46") from the lcd display.
+func renderVolumeBar(vol int, height, width int) string {
+	if height <= 0 {
+		height = 5
+	}
+	if width <= 0 {
+		width = 2
+	}
+	if vol < 0 {
+		vol = 0
+	}
+	if vol > 100 {
+		vol = 100
+	}
+	filled := int(math.Round(float64(vol) * float64(height) / 100.0))
+
+	darkGray := lipgloss.Color("236")
+	green := lipgloss.Color("46")
+
+	var lines []string
+	for i := 0; i < height; i++ {
+		// i=0 is top (high volume), fill from bottom up
+		isFilled := i >= (height - filled)
+		style := lipgloss.NewStyle().
+			Width(width).
+			Background(darkGray)
+		if isFilled {
+			style = style.Background(green)
+		}
+		// use block char for the indicator
+		seg := "█"
+		if !isFilled {
+			seg = " "
+		}
+		lines = append(lines, style.Render(strings.Repeat(seg, width)))
+	}
+	return lipgloss.JoinVertical(lipgloss.Left, lines...)
+}
+
 // searchCmd performs an async station search (used for in-TUI lookups via the filter box).
 func searchCmd(name string) tea.Cmd {
 	return func() tea.Msg {
@@ -539,6 +603,11 @@ type metadataMsg struct {
 	title string
 }
 
+// volumeMsg carries volume level update (0-100).
+type volumeMsg struct {
+	volume int
+}
+
 // metadataPollCmd returns a repeating-ish poll that checks the player's
 // Metadata() and emits updates. (Simple, works whether player is mpvIPC or stub.)
 func metadataPollCmd(p playerpkg.Player) tea.Cmd {
@@ -553,6 +622,23 @@ func metadataPollCmd(p playerpkg.Player) tea.Cmd {
 	})
 }
 
+// volumePollCmd polls the player's Volume() for the vertical bar.
+func volumePollCmd(p playerpkg.Player) tea.Cmd {
+	if p == nil {
+		return nil
+	}
+	return tea.Tick(600*time.Millisecond, func(t time.Time) tea.Msg {
+		v := p.Volume()
+		if v < 0 {
+			v = 0
+		}
+		if v > 100 {
+			v = 100
+		}
+		return volumeMsg{volume: v}
+	})
+}
+
 // Run starts the TUI (alt screen).
 func Run(initial []radio.Station) error {
 	p := tea.NewProgram(NewApp(initial), tea.WithAltScreen())

internal/ui/ui_test.go

@@ -192,6 +192,7 @@ func (stubPlayer) Next() error                          { return nil }
 func (stubPlayer) Prev() error                          { return nil }
 func (stubPlayer) VolumeUp() error                      { return nil }
 func (stubPlayer) VolumeDown() error                    { return nil }
+func (stubPlayer) Volume() int                          { return 65 }
 
 func TestApp_PlaybackView(t *testing.T) {
 	stations := []radio.Station{