[Bug]: reshares: UI indicates owner can add permissions to a reshare -> shows error

⚠️ This issue respects the following points: ⚠️

• This is a bug, not a question or a configuration/webserver/proxy issue.
• This issue is not already reported on Github OR Nextcloud Community Forum (I've searched it).
• Nextcloud Server is up to date. See Maintenance and Release Schedule for supported versions.
• I agree to follow Nextcloud's Code of Conduct.

Bug description

When a user that does not have all permissions reshares a file/folder shared to him, the owner can't add any permissions to the third user that the second user does not have (by design). Though it looks in the UI as if it is possible to add those permissions it is not greyed out. Only when you try to safe it shows an error.

Edit can be selected for share to User3

Error is displayed when updating the share

Steps to reproduce

1. User1 shares to User2 without edit permission
2. User2 shares to User3 without edit permission
3. User1 sees share to User3 and it seems as if User1 could add permissions to the share that User 2 does not have.

Expected behavior

User1 sees Edit permission greyed out, or is able to give User3 edit permission.

Side note

The re-share functionality also has some other weird edge cases still. e.g. in the scenario above. If User2 gets a permission removed the user who received a reshare keeps the permission.

Nextcloud Server version

master

No files or tests are named. Start by reproducing the three-user reshare sequence described in the issue and inspect the permission controls and share-update flow. Done means the Edit permission is greyed out when unavailable, or the owner can grant it without an error, with the related reshare behavior covered as appropriate.