feat(tui): preview each theme as the /theme picker moves

A bare /theme opens the quick picker; moving repaints, Enter keeps and stores the
row, Escape restores the original. /theme list keeps the old listing.

docs/CLI.md

@@ -573,7 +573,12 @@ groups instead of cutting labels in half. Visible labels and execution-setting v
 follow `/language`.
 
 Use `/theme auto|light|dark` to select the terminal background mode, or choose a
-named accent from `/theme`. Both composer borders, the insertion cursor,
+named accent from `/theme`.
+
+- `/theme` alone opens a picker that previews each row as the cursor reaches it.
+- Enter keeps the row, Esc restores the original, and `/theme list` prints the names.
+
+Both composer borders, the insertion cursor,
 selection, scrollbar, and footer use the active CLI theme. See
 [Keyboard shortcuts](./GUIDE.md#keyboard-shortcuts) for transcript navigation,
 multiline input, rewind, and clipboard controls.

docs/CLI.zh-CN.md

@@ -492,7 +492,12 @@ reasonix -p "同时更新两个项目" \
 设定值会跟随 `/language`。
 
 使用 `/theme auto|light|dark` 选择终端背景模式，也可以从 `/theme` 列出的命名配色中选择
-强调色。输入框上下边线、插入光标、选区、滚动条和底栏都会使用当前 CLI 主题。Transcript
+强调色。
+
+- 单独输入 `/theme` 会打开选择器，光标移到哪一行就即时预览。
+- Enter 保留，Esc 还原；`/theme list` 列出名称。
+
+输入框上下边线、插入光标、选区、滚动条和底栏都会使用当前 CLI 主题。Transcript
 导航、多行输入、rewind 和剪贴板操作见[快捷键](./GUIDE.zh-CN.md#快捷键)。
 
 剪贴板操作按内容类型明确分开。本地 transcript 和输入框选区写入系统剪贴板，并且只有写入
@@ -515,7 +520,7 @@ SSH 下远端进程无法读取本机剪贴板，请使用终端粘贴快捷键
 | `/resume [n]` | 搜索最近会话并切换；`/resume <n>` 直接切换到列表中第 n 个会话。 |
 | `/status` | 显示模型、effort、cache、Git、后台任务，以及执行设定或余额信息。 |
 | `/preset [balanced\|delivery]` | 查看或切换 Agent 执行设定（不重建 Controller）；`/work-mode` 与 `/profile` 为兼容别名，`economy`、`light` 都解析为 `balanced`。 |
-| `/theme [auto\|light\|dark\|style]` | 查看或切换 CLI 背景模式和强调色。 |
+| `/theme [auto\|light\|dark\|style\|list]` | 打开选择器预览并切换 CLI 背景模式和强调色。 |
 | `/currency [auto\|CNY\|USD]` | 查看或切换用户全局费用展示币种，并刷新当前运行时。 |
 | `/paste-image` | 读取剪贴板图片并插入可编辑的附件标记。 |
 | `/mouse` | 切换应用内鼠标选区、滚动条和滚轮处理。 |

internal/base/i18n/messages_en.go

@@ -235,7 +235,7 @@ var English = Messages{
 
 	OutputStyleNone:           "no output styles available",
 	ThemeHeader:               "themes:",
-	ThemeHint:                 "switch with /theme <auto|light|dark|style>",
+	ThemeHint:                 "pick with /theme, or switch with /theme <auto|light|dark|style>",
 	ThemeChangedFmt:           "theme switched to %s / %s",
 	ThemeUnknownFmt:           "unknown theme %q",
 	LanguageHeader:            "languages:",

internal/base/i18n/messages_zh.go

@@ -235,7 +235,7 @@ var Chinese = Messages{
 
 	OutputStyleNone:           "没有可用的输出风格",
 	ThemeHeader:               "主题：",
-	ThemeHint:                 "使用 /theme <auto|light|dark|style> 切换",
+	ThemeHint:                 "用 /theme 选择，或用 /theme <auto|light|dark|style> 切换",
 	ThemeChangedFmt:           "已切换主题为 %s / %s",
 	ThemeUnknownFmt:           "未知主题 %q",
 	LanguageHeader:            "语言：",

internal/base/i18n/messages_zh_tw.go

@@ -232,7 +232,7 @@ var ChineseTraditional = Messages{
 
 	OutputStyleNone:           "沒有可用的輸出風格",
 	ThemeHeader:               "主題：",
-	ThemeHint:                 "使用 /theme <auto|light|dark|style> 切換",
+	ThemeHint:                 "用 /theme 選擇，或用 /theme <auto|light|dark|style> 切換",
 	ThemeChangedFmt:           "已切換主題為 %s / %s",
 	ThemeUnknownFmt:           "未知主題 %q",
 	LanguageHeader:            "語言：",

internal/frontend/termrender/theme_switch.go

@@ -45,3 +45,30 @@ func DescribeThemes() string {
 	}
 	return strings.TrimRight(b.String(), "\n")
 }
+
+// RestoreTheme puts back a palette ActiveTheme returned earlier, so a preview
+// that was never confirmed leaves nothing behind.
+func RestoreTheme(p Palette) {
+	activeTheme = p
+	refreshCLIStyles()
+}
+
+// ThemeChoice is one row a theme picker offers: a mode or a named style.
+type ThemeChoice struct {
+	ID          string
+	Description string
+	Active      bool
+}
+
+// ThemeChoices lists the three modes and every style, marking the active style.
+func ThemeChoices() []ThemeChoice {
+	out := []ThemeChoice{
+		{ID: "auto", Description: "follow the terminal background"},
+		{ID: "light", Description: "light palette, current accent kept when it fits"},
+		{ID: "dark", Description: "dark palette, current accent kept when it fits"},
+	}
+	for _, st := range cliThemeStyles {
+		out = append(out, ThemeChoice{ID: st.name, Description: st.mode + " · " + st.description, Active: st.name == activeTheme.Style})
+	}
+	return out
+}

internal/frontend/tui/misc_commands.go

@@ -76,8 +76,43 @@ func (m *model) toggleDiffFold() {
 	m.tr.AddNotice("info", i18n.M.DiffFoldDisabled)
 }
 
+// openThemePicker previews each row as the cursor reaches it and puts the
+// original back unless a row is confirmed. Browsing writes nothing: the
+// preference is stored only through setTheme, as typing the name does.
+func (m *model) openThemePicker() {
+	original := termrender.ActiveTheme()
+	restore := func() {
+		termrender.RestoreTheme(original)
+		termrender.ApplyTextareaTheme(&m.composer)
+	}
+	var items []chooseItem
+	for _, c := range termrender.ThemeChoices() {
+		items = append(items, chooseItem{ID: c.ID, Label: c.ID, Desc: c.Description, Active: c.Active})
+	}
+	p := newQuickPicker(i18n.M.ThemeHeader, items, func(it chooseItem) tea.Cmd {
+		restore()
+		m.setTheme(it.ID)
+		return m.commit()
+	})
+	p.onMove = func(it chooseItem) {
+		restore()
+		if termrender.IsThemeMode(it.ID) {
+			termrender.SetThemeMode(it.ID)
+		} else {
+			termrender.SetThemeStyle(it.ID)
+		}
+		termrender.ApplyTextareaTheme(&m.composer)
+	}
+	p.onCancel = restore
+	m.quick = p
+}
+
 func (m *model) setTheme(name string) {
-	if name == "" {
+	switch strings.ToLower(name) {
+	case "":
+		m.openThemePicker()
+		return
+	case "list":
 		m.tr.AddNotice("info", i18n.M.ThemeHeader+"\n"+termrender.DescribeThemes()+"\n"+i18n.M.ThemeHint)
 		return
 	}

internal/frontend/tui/misc_commands_test.go

@@ -100,7 +100,7 @@ func TestThemeListsSwitchesAndPersists(t *testing.T) {
 	m, k, cfgPath := miscModel(t)
 	prev := termrender.ActiveTheme()
 	t.Cleanup(func() { termrender.SetThemeStyle(prev.Style) })
-	sendLine(m, "/theme")
+	sendLine(m, "/theme list")
 	if got := notices(m); !strings.Contains(got, "graphite") || !strings.Contains(got, i18n.M.ThemeHint) {
 		t.Fatalf("listing = %q", got)
 	}
@@ -205,3 +205,81 @@ func TestThemeAndVerboseNeverWriteIntoAProjectFile(t *testing.T) {
 		t.Fatalf("user config missing the preferences:\n%s", raw)
 	}
 }
+
+func themePickerModel(t *testing.T) (*model, string) {
+	t.Helper()
+	m, _, cfgPath := miscModel(t)
+	termrender.SetThemeStyle("graphite")
+	t.Cleanup(func() { termrender.SetThemeStyle("graphite") })
+	sendLine(m, "/theme")
+	if m.quick == nil {
+		t.Fatal("/theme did not open the picker")
+	}
+	return m, cfgPath
+}
+
+func TestThemePickerPreviewsWhileMovingAndWritesNothing(t *testing.T) {
+	m, cfgPath := themePickerModel(t)
+	before := termrender.ActiveTheme()
+	run(m, press(m, "down"))
+	moved := m.quick.shown()[m.quick.sel]
+	if got := termrender.ActiveTheme(); got.Style == before.Style && got.Name == before.Name {
+		t.Fatalf("moving to %q did not preview it: still %s/%s", moved.ID, got.Name, got.Style)
+	}
+	if _, err := os.Stat(cfgPath); err == nil {
+		t.Fatal("browsing wrote the configuration")
+	}
+	run(m, press(m, "down"))
+	run(m, press(m, "up"))
+	if _, err := os.Stat(cfgPath); err == nil {
+		t.Fatal("browsing wrote the configuration")
+	}
+}
+
+func TestThemePickerEscapeRestoresTheOriginal(t *testing.T) {
+	m, cfgPath := themePickerModel(t)
+	before := termrender.ActiveTheme()
+	for range 3 {
+		run(m, press(m, "down"))
+	}
+	run(m, press(m, "esc"))
+	if m.quick != nil {
+		t.Fatal("Escape left the picker open")
+	}
+	if got := termrender.ActiveTheme(); got != before {
+		t.Fatalf("Escape left %s/%s, want %s/%s", got.Name, got.Style, before.Name, before.Style)
+	}
+	if _, err := os.Stat(cfgPath); err == nil {
+		t.Fatal("cancelling wrote the configuration")
+	}
+}
+
+func TestThemePickerEnterKeepsTheChoiceAndStoresIt(t *testing.T) {
+	m, cfgPath := themePickerModel(t)
+	for m.quick.shown()[m.quick.sel].ID != "glacier" {
+		run(m, press(m, "down"))
+	}
+	run(m, press(m, "enter"))
+	if m.quick != nil {
+		t.Fatal("Enter left the picker open")
+	}
+	if got := termrender.ActiveTheme(); got.Style != "glacier" || got.Name != "light" {
+		t.Fatalf("active = %s/%s, want light/glacier", got.Name, got.Style)
+	}
+	raw, _ := os.ReadFile(cfgPath)
+	if !strings.Contains(string(raw), "glacier") {
+		t.Fatalf("choice not stored:\n%s", raw)
+	}
+}
+
+func TestThemePickerFilterPreviewsTheFirstMatch(t *testing.T) {
+	m, _ := themePickerModel(t)
+	typeText(m, "glac")
+	if got := termrender.ActiveTheme(); got.Style != "glacier" {
+		t.Fatalf("filtering to glacier previewed %s", got.Style)
+	}
+	run(m, press(m, "esc"))
+	if got := termrender.ActiveTheme(); got.Style != "graphite" {
+		t.Fatalf("Escape left %s, want graphite", got.Style)
+	}
+}

internal/frontend/tui/quickpick.go

@@ -26,6 +26,10 @@ type quickPicker struct {
 	query string
 	sel   int
 	pick  func(chooseItem) tea.Cmd
+	// onMove, when set, sees the row under the cursor each time it changes, and
+	// onCancel runs when the picker closes without a choice: a live preview.
+	onMove   func(chooseItem)
+	onCancel func()
 }
 
 func newQuickPicker(title string, items []chooseItem, pick func(chooseItem) tea.Cmd) *quickPicker {
@@ -61,6 +65,10 @@ func (m *model) quickKey(msg tea.KeyPressMsg) (tea.Cmd, bool) {
 	switch k := msg.String(); k {
 	case "esc", "ctrl+c":
 		m.quick = nil
+		if p.onCancel != nil {
+			p.onCancel()
+		}
+		return nil, true
 	case "up", "ctrl+p":
 		p.sel = max(p.sel-1, 0)
 	case "down", "tab", "ctrl+n":
@@ -80,6 +88,11 @@ func (m *model) quickKey(msg tea.KeyPressMsg) (tea.Cmd, bool) {
 			p.query, p.sel = p.query+t, 0
 		}
 	}
+	if p.onMove != nil {
+		if rows := p.shown(); p.sel < len(rows) {
+			p.onMove(rows[p.sel])
+		}
+	}
 	return nil, true
 }
 

release-notes/studio/unreleased/12985.md

@@ -0,0 +1,2 @@
+- 终端界面的 `/theme` 现在打开选择器：光标移到哪一行就即时预览，Enter 保留，Esc 还原；`/theme list` 仍列出名称。关联 #12985。
+- In the terminal UI, `/theme` now opens a picker that previews each row as you move, keeps it on Enter and restores the original on Esc; `/theme list` still prints the names. Refs #12985.