macos: don't put 0x7F as text in key event

Fixes #13869

We already checked `< 0x20` but missed `0x7F` which causes similar
problems.

macos/Sources/Ghostty/Surface View/SurfaceView_AppKit.swift

@@ -1484,11 +1484,12 @@ extension Ghostty {
             var key_ev = event.ghosttyKeyEvent(action, translationMods: translationEvent?.modifierFlags)
             key_ev.composing = composing
 
-            // For text, we only encode UTF8 if we don't have a single control
-            // character. Control characters are encoded by Ghostty itself.
-            // Without this, `ctrl+enter` does the wrong thing.
-            if let text, text.count > 0,
-               let codepoint = text.utf8.first, codepoint >= 0x20 {
+            // Control characters are encoded by Ghostty itself so that the
+            // physical key and its modifiers remain available to protocols
+            // such as the Kitty keyboard protocol.
+            if let text,
+               !text.isEmpty,
+               !text.startsWithASCIIControlCharacter {
                 return text.withCString { ptr in
                     key_ev.text = ptr
                     return ghostty_surface_key(surface, key_ev)

macos/Sources/Helpers/Extensions/String+Extension.swift

@@ -1,4 +1,10 @@
 extension String {
+    /// True when the first scalar is an ASCII control character (C0 or DEL).
+    var startsWithASCIIControlCharacter: Bool {
+        guard let scalar = unicodeScalars.first else { return false }
+        return scalar.value < 0x20 || scalar.value == 0x7F
+    }
+
     func truncate(length: Int, trailing: String = "…") -> String {
         let maxLength = length - trailing.count
         guard maxLength > 0, !self.isEmpty, self.count > length else {

src/input/key_encode.zig

@@ -1359,6 +1359,22 @@ test "kitty: shift+backspace emits CSI u" {
     try testing.expectEqualStrings("\x1b[127;2u", writer.buffered());
 }
 
+test "kitty: alt+backspace emits CSI u" {
+    var buf: [128]u8 = undefined;
+    var writer: std.Io.Writer = .fixed(&buf);
+    try kitty(&writer, .{
+        .key = .backspace,
+        .mods = .{ .alt = true },
+        // macOS may mark Option as consumed while translating the key. With
+        // no attached control text, all modifiers must remain effective.
+        .consumed_mods = .{ .alt = true },
+        .utf8 = "",
+    }, .{
+        .kitty_flags = .{ .disambiguate = true },
+    });
+    try testing.expectEqualStrings("\x1b[127;3u", writer.buffered());
+}
+
 test "kitty: shift+enter emits CSI u" {
     var buf: [128]u8 = undefined;
     var writer: std.Io.Writer = .fixed(&buf);