If you were designing a command-line interface from scratch, you'd definitely make it so that the command prompt gets displayed consistently and reliably after each command terminates, regardless of what garbage it spewed. The only reason we see anything different is because UNIX systems happened to grow that way, and everything gets crammed through an interface that was originally designed to show characters on physical paper.

With the design we actually have, the shell is the only thing in the chain that could reset the TTY state and ensure that the prompt gets displayed consistently each time, and it should. I wouldn't go so far as to say that I expect it to (my expectations for computers are not high in general) but it ought to.

> a command outputting an incomplete line without a line terminator is producing garbled non-textual output

I would argue that no, there are many valid cases for commands to not produce a final \n in their output. The first example that come to mind is curl'ing a REST API whose body is a single line of JSON. Many of those will not bother with a final \n, and this does not qualify as "garbled output" in my book. I would even go as far as saying that a shell just printing the prompt at whatever place the cursor happens to be is a side-effect of how terminal emulation works and the fact it's just a character based terminal.

This is actually something that Warp does pretty well, with a strong integration with the shell where your command is in a dedicated text box, by the virtue of it being GUI and leveraging GUIs. (I don't use it however, I'm too much of a sucker for dense UIs).

However I do agree with your argument that it's not the role of the shell to protect you against `cat /dev/urandom` or `cat picture.png`. And fish indeed does not try.

IMHO a shell is built for humans when in interactive mode (one of the raison d'être of fish), and the lack of final \n is such an annoyance that handling this specific edge case is worth it.

I understand the terminal-garbling issue and know that I should run "reset" in this case (and that it wasn't the shell's fault), but I bet a lot of users who aren't very familiar with this might feel that the shell is "in charge of" the terminal or "in charge of" the whole interaction, and so that it actually should be more proactive in making sure that the terminal is in a visible sensible, usable, understandable state as often as possible -- in this case probably whenever a program exits and a new prompt is displayed?

> The newline is a line terminator, a command outputting an incomplete line without a line terminator is producing garbled non-textual output.

A command could very well be manipulating the cursor on its own and intentionally not writing newlines when it wants to overwrite text such as in a progress bar.