Adds validation that the related page exists, is visible, and that the
user has page edit permissions for the page.
Aligns with attachment permission model, and aligns across different
image endpoints.
Added tests to cover.
Closes#6126
Uploads over the post max size Would previously error without a
clean user facing message. This catches that error to provide a
user friendly message, compatible with our common error handling.
Tested on image manager handling.
Added test to cover.
- Added testing to cover, which was more hassle than thought
since Laravel did not have built in log test helpers, so:
- Added Log testing helper.
Related to #2110
