feat(tui-go): slash command menu in the chat input

Typing `/` as the first char of a chat line opens the command palette inline
(opencode-style), instead of typing a literal slash; mid-line `/` stays literal.
Factors openPalette() (shared with the `p` key) and advertises `/ cmds` in the
insert-mode footer when the line is empty.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

apps/tui-go/internal/app/slash_test.go

@@ -0,0 +1,45 @@
+package app
+
+import (
+	"testing"
+
+	tea "github.com/charmbracelet/bubbletea"
+)
+
+// `/` as the first char of a chat line opens the command palette inline (opencode-style),
+// without typing a literal slash.
+func TestSlashOpensPaletteOnEmptyLine(t *testing.T) {
+	m := NewModel(nil)
+	m.editMode = ModeInsert
+	m.inputMode = ModeRouter
+	m.inputBuffer = ""
+
+	next, _ := m.handleInsertKey(tea.KeyMsg{Type: tea.KeyRunes, Runes: []rune("/")})
+	nm := next.(Model)
+
+	if nm.overlay != OverlayPalette {
+		t.Fatalf("'/' on an empty line should open the palette; overlay=%d", nm.overlay)
+	}
+	if nm.inputBuffer != "" {
+		t.Fatalf("'/' should not be typed literally; buffer=%q", nm.inputBuffer)
+	}
+}
+
+// Mid-line `/` is a literal slash (e.g. a path), not a command trigger.
+func TestSlashLiteralMidLine(t *testing.T) {
+	m := NewModel(nil)
+	m.editMode = ModeInsert
+	m.inputMode = ModeRouter
+	m.inputBuffer = "path"
+	m.inputCursor = len("path")
+
+	next, _ := m.handleInsertKey(tea.KeyMsg{Type: tea.KeyRunes, Runes: []rune("/")})
+	nm := next.(Model)
+
+	if nm.overlay != OverlayNone {
+		t.Fatalf("mid-line '/' must stay literal, not open the palette; overlay=%d", nm.overlay)
+	}
+	if nm.inputBuffer != "path/" {
+		t.Fatalf("mid-line '/' should be typed; buffer=%q", nm.inputBuffer)
+	}
+}

apps/tui-go/internal/app/update.go

@@ -229,9 +229,7 @@ func (m Model) handleNormalKey(k tea.KeyMsg) (tea.Model, tea.Cmd) {
 	case "k":
 		m.navUp()
 	case "p":
-		m.overlay = OverlayPalette
-		m.paletteFilter = ""
-		m.paletteIndex = 0
+		m.openPalette()
 	case "e":
 		m.overlay = OverlayEventInspector
 		m.overlayEventIdx = 0
@@ -408,12 +406,28 @@ func (m Model) handleInsertKey(k tea.KeyMsg) (tea.Model, tea.Cmd) {
 			m.historyNext()
 		}
 	case tea.KeyRunes, tea.KeySpace:
+		// opencode-style slash commands: `/` as the first char of a chat line opens the
+		// command palette inline instead of typing a literal slash. Mid-line `/` is literal.
+		if m.inputMode == ModeRouter && m.inputBuffer == "" && string(k.Runes) == "/" {
+			m.editMode = ModeNormal
+			m.clearInput()
+			m.openPalette()
+			return m, nil
+		}
 		m.appendRunes(string(k.Runes))
 		m.syncFilter()
 	}
 	return m, nil
 }
 
+// openPalette opens the command palette with a cleared filter. Shared by the `p`
+// normal-mode key and the inline `/` trigger in the chat input.
+func (m *Model) openPalette() {
+	m.overlay = OverlayPalette
+	m.paletteFilter = ""
+	m.paletteIndex = 0
+}
+
 // beginIntent stashes the chosen workflow and switches to a text-entry prompt for the
 // freeform request. Submitting sends StartSession(id, intent); an empty line starts with no
 // intent (fixed-task workflows). Esc cancels.

apps/tui-go/internal/app/view.go

@@ -221,6 +221,10 @@ func (m Model) renderFooter() string {
 	switch {
 	case m.editMode == ModeInsert:
 		hints = []string{hint("enter", "send"), hint("esc", "normal"), hint("↑↓", "history")}
+		// The `/` command menu only triggers on an empty chat line (mid-line `/` is literal).
+		if m.inputMode == ModeRouter && m.inputBuffer == "" {
+			hints = append(hints, hint("/", "cmds"))
+		}
 	case m.displayState() == StateApproval:
 		// Approval actions live in the band itself; the footer offers navigation only.
 		hints = []string{hint("l", "back"), hint("e", "events"), hint("q", "quit")}