core: send pixel-level surface sizing to the pty

src/Surface.zig

@@ -894,14 +894,12 @@ pub fn sizeCallback(self: *Surface, size: apprt.SurfaceSize) !void {
 
     // Recalculate our grid size. Because Ghostty supports fluid resizing,
     // its possible the grid doesn't change at all even if the screen size changes.
-    const new_grid_size = renderer.GridSize.init(
+    // We have to update the IO thread no matter what because we send
+    // pixel-level sizing to the subprocess.
+    self.grid_size = renderer.GridSize.init(
         self.screen_size.subPadding(self.padding),
         self.cell_size,
     );
-    if (self.grid_size.equals(new_grid_size)) return;
-
-    // Grid size changed, update our grid size and notify the terminal
-    self.grid_size = new_grid_size;
     if (self.grid_size.columns < 5 and (self.padding.left > 0 or self.padding.right > 0)) {
         log.warn("WARNING: very small terminal grid detected with padding " ++
             "set. Is your padding reasonable?", .{});

src/termio/Exec.zig

@@ -256,10 +256,14 @@ pub fn resize(
     screen_size: renderer.ScreenSize,
     padding: renderer.Padding,
 ) !void {
-    // Update the size of our pty
+    // Update the size of our pty.
     const padded_size = screen_size.subPadding(padding);
     try self.subprocess.resize(grid_size, padded_size);
 
+    // If our grid size didn't change, then we don't need to change
+    // the underlying terminal.
+    if (grid_size.equals(self.grid_size)) return;
+
     // Update our cached grid size
     self.grid_size = grid_size;