fix(file-provider): Deletion of server-side item for items excluded from sync

[claucambra]

Resolves

#10521 (comment)

Summary

Returning NSFileProviderError(.excludedFromSync) from an item creation or modification callback starts a system-managed removal sequence. It does not only report that the operation was rejected. This currently causes an item's standard deletion pipeline to be called, which culminates in a server deletion.

This PR adds a marker for items excluded from sync to prevent this from happening.

Checklist

• Sign-off message is added to all commits.
• The commit history is clean with no merge commits.
  • How to rebase your commits
  • How to squash commits with rebase
• Uploaded screenshots from before and after for UI changes.
• Test(s) added to branch, with before/after results included in PR description, for performance improvements where applicable.
• Documentation has been updated or is not required.
• Backports requested where applicable (critical bugfixes).
• Labels added where applicable (bug/enhancement).
• Milestone added for target version.

[claucambra]

/backport to stable-34.0 please

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[github-actions]

Artifact containing the AppImage: nextcloud-appimage-pr-10534.zip

Digest: sha256:bf5678fb4feca8d0b8792cb7df8f89fd291c738629b03cb4694e75e444ff71f5

To test this change/fix you can download the above artifact file, unzip it, and run it.

Please make sure to quit your existing Nextcloud app and backup your data.

[Rello]

gave it another test with my error example - works nicely

[github-actions]

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[i2h3]

Please note that this is not waterproof because of #10106.