Wrt /issues/show/proj-45:
That would break urls pointing to the old project if the issue
is moved to another project, wouldn't it?
Issues should have the same id even if they are moved. I see
no reason to have project-specific IDs.
Having a "print name" for ids could work though, so
that issue 123 is written as "PROJ-123" everywhere
it's written. But it should still have the same proper handle
IMO, and any inputting of IDs should then accept both 123 and
PROJ-123. But I wouldn't ever use it because...
Another issue with project-local ID numbers is that you can't
ever ever change the prefix. If your customer communication,
version control commits, wiki and everything else refers to issue
"FoodProj-123", then you can't really change FoodProjs
name to EatProj.
I wouldn't use the PROJ-prefix at all, but you go right ahead.
But please don't break globally unique issue IDs. That would
break so many things for so many potential users.