fix(tui): /resume <n> continues the nth saved session in place

In 1.x, "/resume <n>" switches straight to the nth saved session. The Studio
TUI ignored the number and always opened the picker, the known gap left in
the CLI migration tracking issue.

An indexed /resume now resolves the session by its row in the same list the
picker numbers and resumes it, with the same refusals the picker gives: a
running turn, the session already open, or an index outside the list. A bare
/resume (or a non-numeric argument) still opens the picker.

The index lookup shared by /takeover <n> and /rename <n> <title> moves into
one helper so the three commands cannot drift apart.

Refs #11493

docs/CLI.md

@@ -601,7 +601,7 @@ the displayed list matches the commands the TUI accepts.
 | --- | --- |
 | `/model` | Search configured models and switch the active model. |
 | `/provider` | Choose a provider, then choose one of its configured models. |
-| `/resume` | Search recent sessions and switch to one. |
+| `/resume [n]` | Search recent sessions and switch to one; `/resume <n>` switches to the nth session of that list directly. |
 | `/status` | Show model, effort, cache, Git, background jobs, and execution setting or balance details. |
 | `/preset [balanced\|delivery]` | View or change the agent execution setting without rebuilding the controller. `/work-mode` and `/profile` remain compatibility aliases; `economy` and `light` resolve to `balanced`. |
 | `/theme [auto\|light\|dark\|style]` | View or change the CLI background mode and accent palette. |

docs/CLI.zh-CN.md

@@ -512,7 +512,7 @@ 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
 | --- | --- |
 | `/model` | 搜索已配置模型并切换当前模型。 |
 | `/provider` | 选择 provider，再选择该 provider 下的模型。 |
-| `/resume` | 搜索最近会话并切换。 |
+| `/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。 |

internal/frontend/tui/queue_slash.go

@@ -41,6 +41,16 @@ func (m *model) queueSlash(display string) (tea.Cmd, bool) {
 	case "/takeover":
 		running := m.tr.Running
 		run = func() tea.Msg { return m.takeover(fields[1:], running) }
+	case "/resume":
+		if len(fields) != 2 {
+			return nil, false
+		}
+		idx, err := strconv.Atoi(fields[1])
+		if err != nil {
+			return nil, false
+		}
+		running := m.tr.Running
+		run = func() tea.Msg { return m.resumeByIndex(idx, running) }
 	case "/rename":
 		idx, title, ok := renameByIndexArgs(fields, rest)
 		if !ok {
@@ -83,22 +93,48 @@ func (m *model) takeover(args []string, running bool) tea.Msg {
 	}
 	target := args[0]
 	if idx, err := strconv.Atoi(target); err == nil {
-		list, err := m.client.Sessions(m.ctx)
-		if err != nil {
-			return slashDoneMsg{level: "error", text: "takeover: " + err.Error()}
+		s, refused := m.savedSession("takeover", idx)
+		if refused != nil {
+			return *refused
 		}
-		if idx < 1 || idx > len(list) {
-			return slashDoneMsg{level: "info", text: fmt.Sprintf(i18n.M.ResumeBadIndexFmt, len(list))}
-		}
-		if list[idx-1].Current {
+		if s.Current {
 			return slashDoneMsg{level: "info", text: i18n.M.ResumeAlreadyActive}
 		}
-		target = list[idx-1].Path
+		target = s.Path
 	}
 	err := m.client.Resume(m.ctx, target)
 	return takeoverMsg{err: err, text: i18n.M.TakeoverNoSteal}
 }
 
+// resumeByIndex continues the session at idx in the session list in place, as
+// 1.x's "/resume <n>" does; a bare /resume opens the picker instead.
+func (m *model) resumeByIndex(idx int, running bool) tea.Msg {
+	if running {
+		return slashDoneMsg{level: "warn", text: i18n.M.ResumeBusy}
+	}
+	s, refused := m.savedSession("resume", idx)
+	if refused != nil {
+		return *refused
+	}
+	if s.Current {
+		return slashDoneMsg{level: "info", text: i18n.M.ResumeAlreadyActive}
+	}
+	return resumedMsg{err: m.client.Resume(m.ctx, s.Path)}
+}
+
+// savedSession is the session listed at the 1-based idx, or the notice that
+// says why there is none.
+func (m *model) savedSession(cmd string, idx int) (SessionInfo, *slashDoneMsg) {
+	list, err := m.client.Sessions(m.ctx)
+	if err != nil {
+		return SessionInfo{}, &slashDoneMsg{level: "error", text: cmd + ": " + err.Error()}
+	}
+	if idx < 1 || idx > len(list) {
+		return SessionInfo{}, &slashDoneMsg{level: "info", text: fmt.Sprintf(i18n.M.ResumeBadIndexFmt, len(list))}
+	}
+	return list[idx-1], nil
+}
+
 // renameByIndexArgs recognises "/rename <n> <title>", the form that names a
 // saved session by its position; any other shape is the current session's.
 func renameByIndexArgs(fields []string, rest string) (idx int, title string, ok bool) {
@@ -113,14 +149,11 @@ func renameByIndexArgs(fields []string, rest string) (idx int, title string, ok
 }
 
 func (m *model) renameSession(idx int, title string) tea.Msg {
-	list, err := m.client.Sessions(m.ctx)
-	if err != nil {
-		return slashDoneMsg{level: "error", text: "rename: " + err.Error()}
+	s, refused := m.savedSession("rename", idx)
+	if refused != nil {
+		return *refused
 	}
-	if idx < 1 || idx > len(list) {
-		return slashDoneMsg{level: "info", text: fmt.Sprintf(i18n.M.ResumeBadIndexFmt, len(list))}
-	}
-	if err := m.client.RenameSession(m.ctx, list[idx-1].Name, title); err != nil {
+	if err := m.client.RenameSession(m.ctx, s.Name, title); err != nil {
 		return slashDoneMsg{level: "error", text: "rename: " + err.Error()}
 	}
 	return slashDoneMsg{level: "info", text: fmt.Sprintf(i18n.M.RenameDoneFmt, title)}

internal/frontend/tui/queue_slash_test.go

@@ -290,3 +290,41 @@ func TestRenameByIndexTitlesTheNthSavedSession(t *testing.T) {
 		t.Fatalf("out-of-range notice = %q", got)
 	}
 }
+
+// "/resume <n>" continues the nth saved session in place, as 1.x does; a bare
+// /resume still opens the picker.
+func TestResumeByIndexContinuesTheNthSavedSession(t *testing.T) {
+	m, k := queueModel(t, map[string]any{
+		"GET /sessions": []map[string]any{{"name": "a", "path": "/s/a.jsonl", "current": true}, {"name": "b", "path": "/s/b.jsonl"}},
+	})
+	queueSend(m, "/resume 2")
+	if !strings.Contains(k.seen(), `POST /resume {"path":"/s/b.jsonl"}`) {
+		t.Fatalf("resume did not target the second session:\n%s", k.seen())
+	}
+	if m.picker != nil {
+		t.Fatal("an indexed /resume must not open the picker")
+	}
+
+	queueSend(m, "/resume 1")
+	if got := queueLastNotice(m); got != "already in that session" {
+		t.Fatalf("current-session notice = %q", got)
+	}
+	queueSend(m, "/resume 9")
+	if got := queueLastNotice(m); !strings.Contains(got, "1–2") {
+		t.Fatalf("out-of-range notice = %q", got)
+	}
+	m.tr.Running = true
+	queueSend(m, "/resume 2")
+	m.tr.Running = false
+	if got := queueLastNotice(m); got != "finish or cancel the current turn before resuming" {
+		t.Fatalf("mid-turn notice = %q", got)
+	}
+	if n := strings.Count(k.seen(), "POST /resume"); n != 1 {
+		t.Fatalf("refused indexes still reached the kernel (%d resumes):\n%s", n, k.seen())
+	}
+
+	queueSend(m, "/resume")
+	if m.picker == nil {
+		t.Fatal("a bare /resume must open the picker")
+	}
+}