feat: fire OnRequestSendFocus event when DECSET 1004 is enabled

When focus reporting is enabled via DECSET 1004, fire an
OnRequestSendFocus event so consumers can immediately report the
current focus state. This matches the upstream xterm.js behavior.

Fixes #39

Co-authored-by: Ona <no-reply@ona.com>

Author: ona-automations

inputhandler.go

@@ -99,6 +99,7 @@ type InputHandler struct {
 	OnRequestResetEmitter         EventEmitter[struct{}]
 	OnRequestRefreshRowsEmitter   EventEmitter[RowRange]
 	OnColorEmitter                          EventEmitter[[]ColorEvent]
+	OnRequestSendFocusEmitter               EventEmitter[struct{}]
 	OnRequestSyncScrollBarEmitter           EventEmitter[struct{}]
 	OnRequestColorSchemeQueryEmitter        EventEmitter[struct{}]
 	OnRequestWindowsOptionsReportEmitter    EventEmitter[WindowsOptionsReportType]
@@ -563,6 +564,7 @@ func (h *InputHandler) Dispose() {
 	h.OnRequestResetEmitter.Dispose()
 	h.OnRequestRefreshRowsEmitter.Dispose()
 	h.OnColorEmitter.Dispose()
+	h.OnRequestSendFocusEmitter.Dispose()
 	h.OnRequestSyncScrollBarEmitter.Dispose()
 	h.OnRequestColorSchemeQueryEmitter.Dispose()
 	h.OnRequestWindowsOptionsReportEmitter.Dispose()

inputhandler_csi.go

@@ -658,6 +658,7 @@ func (h *InputHandler) setModePrivate(params *Params) bool {
 			h.coreService.DecPrivateModes.MouseTrackingMode = "ANY"
 		case 1004:
 			h.coreService.DecPrivateModes.SendFocus = true
+			h.OnRequestSendFocusEmitter.Fire(struct{}{})
 		case 1006:
 			h.coreService.DecPrivateModes.MouseEncoding = "SGR"
 		case 1016:

inputhandler_csi_test.go

@@ -1856,6 +1856,83 @@ func TestWindowOptionsReportTerminalLevel(t *testing.T) {
 	})
 }
 
+// --- OnRequestSendFocus (DECSET 1004) tests ---
+
+func TestOnRequestSendFocus(t *testing.T) {
+	t.Parallel()
+
+	t.Run("fires_when_focus_reporting_enabled", func(t *testing.T) {
+		t.Parallel()
+		h := newTestInputHandler(80, 24)
+		fired := 0
+		h.OnRequestSendFocusEmitter.Event(func(struct{}) {
+			fired++
+		})
+
+		// Enable focus reporting (DECSET 1004).
+		h.ParseString("\x1b[?1004h")
+
+		if fired != 1 {
+			t.Errorf("expected OnRequestSendFocus to fire once, got %d", fired)
+		}
+	})
+
+	t.Run("does_not_fire_when_focus_reporting_disabled", func(t *testing.T) {
+		t.Parallel()
+		h := newTestInputHandler(80, 24)
+		fired := 0
+		h.OnRequestSendFocusEmitter.Event(func(struct{}) {
+			fired++
+		})
+
+		// Disable focus reporting (DECRST 1004) without enabling first.
+		h.ParseString("\x1b[?1004l")
+
+		if fired != 0 {
+			t.Errorf("expected OnRequestSendFocus not to fire, got %d", fired)
+		}
+	})
+
+	t.Run("fires_each_time_focus_reporting_enabled", func(t *testing.T) {
+		t.Parallel()
+		h := newTestInputHandler(80, 24)
+		fired := 0
+		h.OnRequestSendFocusEmitter.Event(func(struct{}) {
+			fired++
+		})
+
+		// Enable, disable, enable again.
+		h.ParseString("\x1b[?1004h")
+		h.ParseString("\x1b[?1004l")
+		h.ParseString("\x1b[?1004h")
+
+		if fired != 2 {
+			t.Errorf("expected OnRequestSendFocus to fire twice, got %d", fired)
+		}
+	})
+}
+
+func TestOnRequestSendFocusTerminalLevel(t *testing.T) {
+	t.Parallel()
+
+	t.Run("DECSET_1004_forwarded_to_terminal", func(t *testing.T) {
+		t.Parallel()
+		term := newTestTerminal(80, 24)
+		defer term.Dispose()
+
+		fired := false
+		d := term.OnRequestSendFocus(func() {
+			fired = true
+		})
+		defer d.Dispose()
+
+		term.WriteString("\x1b[?1004h")
+		if !fired {
+			t.Fatal("Terminal.OnRequestSendFocus not fired for DECSET 1004")
+		}
+	})
+}
+
 // --- VtExtensions gating tests ---
 
 func TestVtExtensions_Win32InputModeGating(t *testing.T) {

terminal.go

@@ -59,6 +59,7 @@ type Terminal struct {
 	OnScrollEmitter                  EventEmitter[int]
 	OnRenderEmitter                  EventEmitter[RowRange]
 	OnWriteParsedEmitter             EventEmitter[struct{}]
+	OnRequestSendFocusEmitter               EventEmitter[struct{}]
 	OnRequestColorSchemeQueryEmitter        EventEmitter[struct{}]
 	OnRequestWindowsOptionsReportEmitter    EventEmitter[WindowsOptionsReportType]
 }
@@ -97,6 +98,7 @@ func New(opts ...Option) *Terminal {
 	ih.OnLineFeedEmitter.Event(func(struct{}) { t.OnLineFeedEmitter.Fire(struct{}{}) })
 	ih.OnCursorMoveEmitter.Event(func(struct{}) { t.OnCursorMoveEmitter.Fire(struct{}{}) })
 	ih.OnRequestRefreshRowsEmitter.Event(func(r RowRange) { t.OnRenderEmitter.Fire(r) })
+	ih.OnRequestSendFocusEmitter.Event(func(struct{}) { t.OnRequestSendFocusEmitter.Fire(struct{}{}) })
 	ih.OnRequestColorSchemeQueryEmitter.Event(func(struct{}) { t.OnRequestColorSchemeQueryEmitter.Fire(struct{}{}) })
 	ih.OnRequestWindowsOptionsReportEmitter.Event(func(rt WindowsOptionsReportType) { t.OnRequestWindowsOptionsReportEmitter.Fire(rt) })
 
@@ -280,6 +282,13 @@ func (t *Terminal) OnRender(fn func(RowRange)) Disposable {
 	return t.OnRenderEmitter.Event(fn)
 }
 
+// OnRequestSendFocus subscribes to focus-reporting enable events (DECSET 1004).
+// Fired when the application enables focus tracking so the host can immediately
+// report the current focus state.
+func (t *Terminal) OnRequestSendFocus(fn func()) Disposable {
+	return t.OnRequestSendFocusEmitter.Event(func(struct{}) { fn() })
+}
+
 // OnRequestColorSchemeQuery subscribes to DSR 996 color scheme query events.
 // Fired when the client sends CSI ? 996 n while color scheme updates (DECSET 2031) are enabled.
 func (t *Terminal) OnRequestColorSchemeQuery(fn func()) Disposable {
@@ -447,6 +456,7 @@ func (t *Terminal) Dispose() {
 	t.OnScrollEmitter.Dispose()
 	t.OnRenderEmitter.Dispose()
 	t.OnWriteParsedEmitter.Dispose()
+	t.OnRequestSendFocusEmitter.Dispose()
 	t.OnRequestColorSchemeQueryEmitter.Dispose()
 	t.OnRequestWindowsOptionsReportEmitter.Dispose()
 }