Source editing mode could be switched on and used via API even if plugin disabled

[f1ames]

📝 Provide detailed reproduction steps (if any)

1. Go to https://ckeditor.com/docs/ckeditor5/latest/examples/builds-custom/full-featured-editor.html.
2. Open browser dev console.
3. Run editor.plugins.get('SourceEditing').isEnabled = false.
   • Source Editing plugin gets disabled.
4. Run editor.plugins.get('SourceEditing').isSourceEditingMode = true.
   • Editor is switched to source editing mode.
5. Types something in the editor.
6. Run editor.plugins.get('SourceEditing').isSourceEditingMode = false.

Screen.Recording.2025-01-10.at.11.23.26.mov

✔️ Expected result

I would expect that plugin will not react to switching to source mode via public API when being disabled.

❌ Actual result

It's possible to switch to source mode while plugin is disabled. What's more, modifying content in source mode and switching back, propagates it, modifying the content in WYSIWYG mode - all while Source Editing plugin is disabled.

Additional thoughts

I know that both isEnabled and isSourceEditingMode are public API so both can be easily changed by 3rd-party integration/action. Still, the behavior seems inconsistent and may be confusing for someone trying to integrate with it.

❓ Possible solution

...

📃 Other details

• Browser: Chrome
• OS: macOS
• First affected CKEditor version: Not sure, checked on latest stable 44.1.0
• Installed CKEditor plugins: SourceEditing

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