Laurent, the non desruptive way to achieve that would be to have an .vscode/extensions.json file with
{
"recommendations": [
"cSpell"
]
}
Me too, and that config file doesn't override this. Normally it should take the one setting with have in this file (cspell) and apply this, but anything else should remain unchanged.
I think you are getting mixed up between the global and project-specific settings. It's true, if I have no project-specific settings and only the global ones, then it would work as you described. But I create a project-specific .vscode/settings for each of my projects. Why? Because some of my global settings need to be overridden. For example I use prettier in my global settings, joplin doesn't, so I need to turn off prettier in the joplin/.vscode/settings.json. But I can't, because you have committed that file to the repo, so it is no longer my personal file, it is shared with everyone who works on this project.