window-size-fixed

window-size-fixed is a variable defined in `window.el'.
Its value is

nil

• Automatically becomes buffer-local when set.

Documentation:
Non-nil in a buffer means windows displaying the buffer are fixed-size.
If the value is `height', then only the window's height is fixed.
If the value is `width', then only the window's width is fixed.
Any other non-nil value fixes both the width and the height.

Emacs won't change the size of any window displaying that buffer,
unless it has no other choice (like when deleting a neighboring
window).