You're setting up a page for the first time. You type "Our Services" as the title, hit create, and Cantrip turns that into a URL: yoursite.com/our-services. Fine, for now. A few weeks later you decide "Services" reads cleaner without the "Our," or you catch a typo, or you just want the address to match how you actually talk about the page everywhere else. You go looking for the field that fixes it.
There isn't one. You can rename the page's title as many times as you want, and the text at the top of the page and the label in your navigation update instantly. The URL doesn't move. It's set once, straight from whatever the title happened to be the moment you hit create, and there's no setting in Cantrip that changes it after that. Not in the page editor, not anywhere else.
Posts work differently. A post's slug isn't locked at creation. You can go back and change it any time after it's published. That sounds like the fix pages are missing, until you notice what's missing on the post side instead: there's no redirect. Change a post's URL after it's been live, and the old address doesn't forward anyone anywhere. It just stops working. Anyone with the old link, whether that's a customer's bookmark or a page Google already indexed, hits a dead end the next time they click it.
So neither side is actually safe to change your mind on. Pages lock the URL in before you've had a real chance to think it through. Posts let you change it, then quietly punish you for doing so. I'd build it the other way if I were starting from scratch: careful about page URLs since those tend to matter for years, looser about posts since most of them don't. That's not how it works right now, so plan around it instead.
For pages, the fix is boring but it works: think about the actual URL before you hit create, not just the title. "About" reads fine as both a title and an address. "The Story Behind Our Shop, Part One" doesn't, and you'll be looking at that exact URL for as long as the page exists. Type the title the way you want the address to read, or close to it, and you skip the problem instead of finding it three weeks later.
For posts, the rule is simpler: don't touch a slug once it's live and linked anywhere you don't control. Fixing a typo on something you published an hour ago and haven't shared yet? Go ahead. Renaming a post that's been up for a year, has search traffic, or that someone else linked to? That's a real cost, not a cosmetic tweak, and it's worth thinking through before you hit save.