fix(editor): partially disable at mention in code block

[chloelee767]

Hello, this is a PR to disable the at-symbol to insert note links and slash commands inside code blocks, by disabling the mention plugin in code blocks. Note that this fix only affects code blocks, not inline code. Ideally I would like to disable the plugin for inline code too, but I haven't figured how to do that.

Known issues:

There still seems to be some kind of race condition that causes the at-symbol or slash commands to trigger inside the code block sometimes, when moving quickly from a text region to a code block using the mouse or arrow keys – see the video below.

Screen.Recording.2026-01-31.at.11.53.21.PM.mov

Scenarios tested:

• at mention and slash commands still work in regular text
• at mention and slash commands are no longer triggered in code blocks
• ~ and # inside the note attributes popup section still works (since my understanding is they are also implemented using the mention plugin)

I frankly don't know much about ckeditor, so I'm too not sure if this approach is a good idea or have any unintended side effects (I also notice there's already an upstream issue ckeditor/ckeditor5#19146 , so I'm not sure if the preference is to wait for the issue to be fixed upstream instead), but I personally haven't noticed any issues in the couple of weeks I've been test driving this.

Partially solves #8322

[gemini-code-assist]

Summary of Changes

Hello @chloelee767, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses an undesirable behavior in CKEditor 5 where the mention plugin, used for note links and slash commands, would incorrectly activate within code blocks. By introducing a dedicated plugin, DisableMentionInCodeBlock, the change ensures that the mention functionality is selectively disabled only within code block regions, thereby improving the editing experience and preventing unintended autocomplete popups. The solution maintains full mention functionality in regular text areas and includes new tests to validate its effectiveness.

Highlights

• Disable Mentions in Code Blocks: Implemented a new CKEditor 5 plugin, DisableMentionInCodeBlock, to prevent the mention feature (at-symbols and slash commands) from triggering inside code blocks.
• Schema Configuration: Configured the CKEditor 5 schema to disallow the 'mention' attribute within codeBlock $text contexts, ensuring mentions only work in regular text.
• New Testing Framework: Introduced Vitest for testing, adding new test files and a configuration to verify the correct behavior of the new plugin.
• Dependency and Script Updates: Updated package.json with new development dependencies and test scripts to support the Vitest testing framework.

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[gemini-code-assist]

Code Review

Thank you for this contribution. This PR introduces a clever solution to disable mentions within code blocks by creating a custom CKEditor plugin that modifies the schema. The approach is sound and the inclusion of unit tests with the new Vitest setup is excellent, ensuring the change is robust.

I've found one critical issue in package.json with a duplicate dependency that needs to be addressed. Otherwise, the changes look great. Well done!