Implement the XTWINOPS (CSI t) control sequences that "make sense".

These sequences were implemented:

CSI 14 t - report the text area size in pixels
CSI 16 t - report the cell size in pixels
CSI 18 t - report the text area size in cells
CSI 21 t - report the window title

These sequences were not implemented because they manuipulate the window
state in ways that we do not want.

CSI 1 t
CSI 2 t
CSI 3 ; x ; y t
CSI 4 ; height ; width ; t
CSI 5 t
CSI 6 t
CSI 7 t
CSI 8 ; height ; width ; t
CSI 9 ; 0 t
CSI 9 ; 1 t
CSI 9 ; 2 t
CSI 9 ; 3 t
CSI 10 ; 0 t
CSI 10 ; 1 t
CSI 10 ; 2 t
CSI 24 t

These sequences were not implemented because they do not make sense in
a Wayland context:

CSI 11 t
CSI 13 t
CSI 14 ; 2 t

These sequences were not implemented because they provide information
about the screen that is unnecessary.

CSI 15 t
CSI 19 t

These sequences were not implemeted because Ghostty does not maintain an
icon title for windows.

CSI 20 t
CSI 22 ; 0 t
CSI 22 ; 1 t
CSI 23 ; 0 t
CSI 23 ; 1 t

These sequences were not implemented because of the additional
complexity of maintaining a stack of window titles.

CSI 22 ; 2 t
CSI 23 ; 2 t

src/apprt/embedded.zig

@@ -55,6 +55,9 @@ pub const App = struct {
         /// Called to set the title of the window.
         set_title: *const fn (SurfaceUD, [*]const u8) callconv(.C) void,
 
+        /// Called to get the title of the window.
+        get_title: ?*const fn (SurfaceUD) callconv(.C) ?[*]const u8 = null,
+
         /// Called to set the cursor shape.
         set_mouse_shape: *const fn (SurfaceUD, terminal.MouseShape) callconv(.C) void,
 
@@ -543,6 +546,17 @@ pub const Surface = struct {
         );
     }
 
+    pub fn getTitle(self: *Surface) ?[:0]const u8 {
+        const func = self.app.opts.get_title orelse {
+            log.info("runtime embedder does not support get_title", .{});
+            return null;
+        };
+
+        const result = func(self.userdata);
+        if (result == null) return null;
+        return std.mem.sliceTo(@as([*:0]const u8, @ptrCast(result.?)), 0);
+    }
+
     pub fn setMouseShape(self: *Surface, shape: terminal.MouseShape) !void {
         self.app.opts.set_mouse_shape(
             self.userdata,

src/apprt/glfw.zig

@@ -360,6 +360,11 @@ pub const Surface = struct {
     /// The monitor dimensions so we can toggle fullscreen on and off.
     monitor_dims: MonitorDimensions,
 
+    /// Save the title text so that we can return it later when requested.
+    /// This is allocated from the heap so it must be freed when we deinit the
+    /// surface.
+    title_text: ?[:0]const u8 = null,
+
     pub const Options = struct {};
 
     /// Initialize the surface into the given self pointer. This gives a
@@ -463,6 +468,8 @@ pub const Surface = struct {
     }
 
     pub fn deinit(self: *Surface) void {
+        if (self.title_text) |t| self.core_surface.alloc.free(t);
+
         // Remove ourselves from the list of known surfaces in the app.
         self.app.app.deleteSurface(self);
 
@@ -609,7 +616,14 @@ pub const Surface = struct {
 
     /// Set the title of the window.
     pub fn setTitle(self: *Surface, slice: [:0]const u8) !void {
-        self.window.setTitle(slice.ptr);
+        if (self.title_text) |t| self.core_surface.alloc.free(t);
+        self.title_text = try self.core_surface.alloc.dupeZ(u8, slice);
+        self.window.setTitle(self.title_text.?.ptr);
+    }
+
+    /// Return the title of the window.
+    pub fn getTitle(self: *Surface) ?[:0]const u8 {
+        return self.title_text;
     }
 
     /// Set the shape of the cursor.

src/apprt/gtk/Surface.zig

@@ -935,6 +935,10 @@ pub fn setTitle(self: *Surface, slice: [:0]const u8) !void {
     self.updateTitleLabels();
 }
 
+pub fn getTitle(self: *Surface) ?[:0]const u8 {
+    return self.title_text;
+}
+
 pub fn setMouseShape(
     self: *Surface,
     shape: terminal.MouseShape,

src/apprt/surface.zig

@@ -18,6 +18,9 @@ pub const Message = union(enum) {
     /// of any length
     set_title: [256]u8,
 
+    /// Report the window title back to the terminal
+    report_title: ReportTitleStyle,
+
     /// Set the mouse shape.
     set_mouse_shape: terminal.MouseShape,
 
@@ -57,6 +60,10 @@ pub const Message = union(enum) {
 
     /// Report the color scheme
     report_color_scheme: void,
+
+    pub const ReportTitleStyle = enum {
+        csi_21_t,
+    };
 };
 
 /// A surface mailbox.