message: What I really needed was a lunch break
  checkpointing this since it's so close. It works for everything but fullscreen on my primary, 125% display which has the taskbar on top, and autohides. Every other case works fine.
diff: @@ -332,6 +332,8 @@ int NonClientIslandWindow::_GetResizeHandleHeight() const noexcept
  // default frame.
  const auto originalTop = params->rgrc[0].top;
  + const auto originalSize = params->rgrc[0];
  +
  // apply the default frame
  auto ret = DefWindowProc(_window.get(), WM_NCCALCSIZE, wParam, lParam);
  if (ret != 0)
  @@ -347,6 +349,8 @@ int NonClientIslandWindow::_GetResizeHandleHeight() const noexcept
  }
  auto newTop = originalTop;
  + auto newSize = params->rgrc[0];
  + newSize.top = newTop;
  // WM_NCCALCSIZE is called before WM_SIZE
  _UpdateMaximizedState();
  @@ -359,11 +363,69 @@ int NonClientIslandWindow::_GetResizeHandleHeight() const noexcept
  // then the window is clipped to the monitor so that the resize handle
  // do not appear because you don't need them (because you can't resize
  // a window when it's maximized unless you restore it).
  - newTop += _GetResizeHandleHeight();
  + newSize.top += _GetResizeHandleHeight();
  + // newTop += _GetResizeHandleHeight();
  + }
  +
  + // // only modify the top of the frame to remove the title bar
  + // params->rgrc[0].top = newTop;
  +
  + HMONITOR hMon = MonitorFromWindow(_window.get(), MONITOR_DEFAULTTONULL);
  + if (hMon && (_isMaximized || _fullscreen))
  + {
  + MONITORINFO monInfo{ 0 };
  + monInfo.cbSize = sizeof(MONITORINFO);
  + auto res = GetMonitorInfo(hMon, &monInfo);
  + res;
  +
  + // SHAppBarMessage(ABM_GETTASKBARPOS, &data);
  +
  + APPBARDATA autohide{ 0 };
  + autohide.cbSize = sizeof(autohide);
  + UINT state = (UINT)SHAppBarMessage(ABM_GETSTATE, &autohide);
  +
  + if (WI_IsFlagSet(state, ABS_AUTOHIDE))
  + {
  + auto hasAutohideTaksbar = [&monInfo](const UINT edge) -> bool {
  + APPBARDATA data{ 0 };
  + data.cbSize = sizeof(data);
  + data.uEdge = edge;
  + data.rc = monInfo.rcMonitor;
  + HWND hTaskbar = (HWND)SHAppBarMessage(ABM_GETAUTOHIDEBAREX, &data);
  + return hTaskbar != nullptr;
  + };
  + const bool onTop = hasAutohideTaksbar(ABE_TOP);
  + const bool onBottom = hasAutohideTaksbar(ABE_BOTTOM);
  + const bool onLeft = hasAutohideTaksbar(ABE_LEFT);
  + const bool onRight = hasAutohideTaksbar(ABE_RIGHT);
  +
  + if (onTop)
  + {
  + newSize.top += 2;
  + // newBottom -= 2;
  + }
  + if (onBottom)
  + {
  + newSize.bottom -= 2;
  + }
  + if (onLeft)
  + {
  + newSize.left += 2;
  + }
  + if (onRight)
  + {
  + newSize.right -= 2;
  + }
  + }
  }
  - // only modify the top of the frame to remove the title bar
  - params->rgrc[0].top = newTop;
  + auto a = 0;
  + a++;
  + a;
  + newSize;
  + newTop;
  + params->rgrc[0] = newSize;
  + // params->rgrc[0].top = newTop;
  return 0;
  }
  