nix flakes' # does not play nice with zsh when extendedGlob is enabled.

Here's a simple example...

> setopt extendedGlob                                                         
> nix profile install nixpkgs#hello            
Found existing alias for "nix". You should use: "n"
zsh: no matches found: nixpkgs#hello

Here's a workaround.

> unsetopt extendedGlob    
> nix profile install nixpkgs#hello  

...works

Any command that uses the # in the command is likely affected.

Many people will have extended glob enable automatically if they use zsh configuration frameworks such as oh-my-zsh.

Took a long time for me to realize this was a zsh issue more than a nix flakes issue. Might suggest that the resource path not include a # going forward.

This issue can be closed, but parking it here so people can find it when they search.