Temporary page __new__ is not deleted after creating the real page

[bezin]

Description

The temporary page with slug __new__ will not be deleted after the actual page has been created. As this temporary file contains a page UUID, this will be reused when creating another page, leading to duplicate UUIDs.

In my case, I want to use the uuid as the slug (as I don't care about the slug at all in this particular care). This is why it crashes right in the page creation dialog, because there already is a page with the same slug. I would expect the temporary __new__ page to be deleted in this case, too.

Expected behavior
I can create multiple pages one after another without any issue.

Screenshots

To reproduce

1. Have the following create option for a page:

create:
  title:
    label: Veranstaltungstitel
  slug: "{{ page.uuid }}"

2. Create a new page with any title
3. Create another page with any title

Your setup

Kirby 4.6.1
PHP 8.4
MacOS 15.3.1

[distantnative]

Similar to #6640 and not fixable before we have pure virtual pages (currently they can be still written to the content folder, which is what happens when you call page.uuid when no UUID exists yet - it has to be created and then stored right away).

For a future solution, I think we need to do roughly the following steps when the dialog gets submitted:

• Start creating a page instance with MemoryStorage
• Keep track of this throughout the submit handling
• Use it to resolve field templates
• Use it to validate etc.
• Once all of this has succeeded, change storage to PlainTextStorage (or technically any storage that the page object had initially)

[jonasfeige]

Just a head's up that this issue can apparently also be caused by a field within the page's blueprint.
Ran into the same problem only with this and nothing in the create dialogue.

unqiueId:
  label: ID (Intern)
  type: info
  text: "{{ page.uuid.id }}"

I remembered reading in the Forums about a better way to retrieve the Uuid ($this->content()->get('uuid')), and this indeed works without issue.