Add Xorg Remote controller capture with a core F11 escape

The Xorg command owner gains an exclusive Remote capture mode. Native
transitions pass through the repeat normalizer and capture router;
forwarded keys leave as remote.input events, Remote's own shortcuts are
dispatched locally, and F11 ends capture on the X thread. Reader policy,
overflow or inconsistent input also end it. Ending releases forwarded
keys first and keeps the grab until held keys are released. Local key
echo is suppressed during capture. The app attaches the owner to
sessions installed with keyboard-capture.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/input/remote_capture.go

@@ -17,6 +17,49 @@ type RemoteCaptureKey struct {
 	Symbol  uint32
 	Pressed bool
 	Repeat  bool
+	// Unsupported marks a fresh press the Remote key vocabulary cannot name.
+	// It is consumed locally with its repeats and release, never forwarded.
+	Unsupported bool
+}
+
+// RemoteCaptureEvent is one item from a native capture owner to its reader
+// consumer. Exactly one of Key or Ended is set. Name is present only on a
+// fresh press. Ended reports why capture stopped: "escape", "requested" or
+// "local" (reader policy, overflow or an inconsistent native stream); no
+// further events follow it.
+type RemoteCaptureEvent struct {
+	Key   *RemoteCaptureTransition
+	Ended string
+}
+
+type RemoteCaptureTransition struct {
+	Code    uint8
+	Name    string
+	Pressed bool
+	Repeat  bool
+}
+
+// RemoteCaptureEscape is the core escape chord: F11 with no modifiers. It is
+// handled by the native owner without waiting for the network or a Tentacle.
+var RemoteCaptureEscape = CommandChord{Symbol: 0xffc8}
+
+// RemoteCaptureKeyName returns the canonical Remote key name for a
+// group-zero, level-zero keysym name, or "" when it has none.
+func RemoteCaptureKeyName(keysym string) string {
+	switch keysym {
+	case "Prior":
+		keysym = "Page_Up"
+	case "Next":
+		keysym = "Page_Down"
+	case "KP_Prior":
+		keysym = "KP_Page_Up"
+	case "KP_Next":
+		keysym = "KP_Page_Down"
+	}
+	if !ValidRemoteKeyName(keysym) {
+		return ""
+	}
+	return keysym
 }
 
 // RemoteCaptureResult is the routing decision for one captured transition.
@@ -164,6 +207,10 @@ func (router *RemoteCaptureRouter) Route(key RemoteCaptureKey) (RemoteCaptureRes
 	if len(router.order) >= RemoteHeldKeyLimit {
 		return router.fail(ErrRemoteKeyLimit)
 	}
+	if key.Unsupported {
+		router.hold(code, remoteCaptureLocal)
+		return RemoteCaptureResult{}, nil
+	}
 	if mask, modifier := remoteModifierMask(key.Symbol); modifier || router.cthulhu[key.Symbol] {
 		router.hold(code, remoteCaptureForwarded)
 		router.modifier[code] = true

internal/input/remote_capture_test.go

@@ -305,3 +305,19 @@ func TestBehaviorRemoteCaptureComposesWithNormalizer(t *testing.T) {
 		t.Fatalf("commands = %v", commands)
 	}
 }
+
+func TestBehaviorRemoteCaptureConsumesUnsupportedKeys(t *testing.T) {
+	router := newTestCaptureRouter(t, nil)
+	runCaptureSteps(t, router, []captureStep{
+		{press(codeShift, leftShiftKeySymbol), remote(down(codeShift))},
+		{RemoteCaptureKey{Keycode: 121, Symbol: 0x1008ff12, Pressed: true, Unsupported: true}, RemoteCaptureResult{}},
+		{hold(121, 0x1008ff12), RemoteCaptureResult{}},
+		{release(121), RemoteCaptureResult{}},
+		{release(codeShift), remote(up(codeShift))},
+	})
+	for keysym, want := range map[string]string{"Prior": "Page_Up", "KP_Next": "KP_Page_Down", "a": "a", "A": "", "XF86AudioMute": "", "ISO_Level3_Shift": ""} {
+		if got := RemoteCaptureKeyName(keysym); got != want {
+			t.Fatalf("%s = %q, want %q", keysym, got, want)
+		}
+	}
+}