>A TUI can't prevent the user from copying text by its very nature.

Funny but I struggle with copying anything in most recent TUIs. Fancy padding or multiplexer borders and multiple lines of text? It breaks. Incomplete text in a spreadsheet column (tabiew) or a narrow internal window? It breaks. Ohmypi literally has a separate command to copy the prompt because of that, and another command to copy the model reply. TUI is just a poor choice here, it doesn't play well with formatted text like markdown, UI controls, long text, and so on. Terminals are good for CLI where the text is presented as lines, not TUI with spaced layout.

>Any terminal can implement this kind of arbitrary-text keyboard navigation on its own and have it work for all TUIs. Were e.g. GTK to implement something like this, it would only work for GTK apps, not for all GUI apps. This is exclusive of TUIs because TUIs are text-driven while GUIs are pixel-driven.

Terminal navigation has nothing to do with TUI navigation. Most TUI apps suffer from terrible NIH and end up with their own homegrown incompatible keyboard navigation schemas you need to learn every time. Of course absolutely nothing prevents you from writing a TUI framework with a common schema, at which point you will be at the mercy of the dev using this or that framework and schema, same as with GTK and Qt. None of this is unique to TUIs or GUIs.