feat(tui): add /undo and /revert commands

internal/tui/commands.go

@@ -34,7 +34,9 @@ func init() {
 		{"theme", "Pick the colour theme (Ctrl+T)", (*Model).cmdTheme},
 		{"reasoning", "Toggle reasoning display", (*Model).cmdReasoning},
 		{"clear", "Clear the transcript", (*Model).cmdClear},
+		{"revert", "Revert to an earlier turn (picker)", (*Model).cmdRevert},
 		{"stop", "Interrupt the current turn", (*Model).cmdStop},
+		{"undo", "Undo the last turn", (*Model).cmdUndo},
 		{"status", "Runtime summary", (*Model).cmdStatus},
 		{"web", "Print the dashboard URL", (*Model).cmdWeb},
 		{"version", "Show the version", (*Model).cmdVersion},

internal/tui/tui.go

@@ -89,6 +89,11 @@ type Model struct {
 	picker picker
 	input  inputModal
 
+	// pending is a staged /undo or /revert awaiting the operator's "y" to
+	// commit. Nil when nothing is pending; a pointer keeps the hot-path
+	// check cheap (nil vs zero-valued struct).
+	pending *pendingRevert
+
 	cache map[string]string // memoised block renders, keyed by content+width
 
 	welcomeFrame int // animation frame for the empty-state splash
@@ -260,6 +265,29 @@ func (m *Model) onKey(msg tea.KeyMsg) (tea.Model, tea.Cmd) {
 		return m, m.modalCmd()
 	}
 
+	// A staged /undo or /revert intercepts the next keystroke: "y" (with
+	// an empty composer) commits, Esc discards, everything else discards
+	// and falls through so the keystroke still lands normally. Placed
+	// above the palette check so a stray key while a rollback is pending
+	// never silently disappears into palette navigation.
+	if m.pending != nil {
+		if m.ta.Value() == "" {
+			if r := msg.Runes; len(r) == 1 && (r[0] == 'y' || r[0] == 'Y') {
+				m.commitPending()
+				m.refreshTranscript()
+				return m, nil
+			}
+			if msg.Type == tea.KeyEsc {
+				m.cancelPending()
+				m.refreshTranscript()
+				return m, nil
+			}
+		}
+		m.cancelPending()
+		m.refreshTranscript()
+		// fall through so the keystroke still routes as normal input
+	}
+
 	// Palette navigation takes priority.
 	if len(m.palette) > 0 {
 		switch msg.Type {