Do you have an example? None of the command-line tools I use every day work that way. The usual workflow is 1- type a couple characters; 2- press <tab> to complete. The second step is crucial because it ensures you run the right command.
For conflicts (does 'd' refer to delete or disable?) the more commonly used command is usually what the abbreviation will expand to (so GDB accepts 'd' for "delete").
git has something similar, although it's disabled by default (help.autocorrect option).
> npm and gem behave like this
No, `npm` has a couple aliases like "i" for "install", but you can’t use "in", "ins", "insta", etc. It has "view" and "version" but "v" is an alias for "view".
`gem` does work like this (#TIL), although it has some hard-coded aliases: while its help page says "Commands may be abbreviated, so long as they are unambiguous", `gem i` works as `gem install` even if there’s a command "info". If you try `gem in`, it does complain that it’s ambiguous.