Hide message notification content by default when the app is locked

[bxdxnn]

Content

New setting (enabled by default, not shown when the app PIN code is not setup) that makes the app use the fallback notification (the "You have (count) new messages" notification) when the app is closed (i.e. locked).

Motivation and context

ATM you can still read and reply from the notifications on new messages even when the app is locked, which almost defeats the entire purpose of having an app PIN lock.

Screenshots / GIFs

Tests

Setup the "Screen lock" PIN code

• Have the option enabled
  • Have the app opened
    • You should receive notifications normally
  • Have the app closed
    • You should receive the fallback notification
• Have the option disabled
  • You should receive notifications normally

Tested devices

• Physical
• Emulator
• OS version(s): 16

Checklist

• This PR was made with the help of AI:
  • Yes. In this case, please request a review by Copilot.
  • No.
• Changes have been tested on an Android device or Android emulator with API 24
• UI change has been tested on both light and dark themes
• Accessibility has been taken into account. See https://github.com/element-hq/element-x-android/blob/develop/CONTRIBUTING.md#accessibility
• Pull request is based on the develop branch
• Pull request title will be used in the release note, it clearly defines what will change for the user
• Pull request includes screenshots or videos if containing UI changes
• You've made a self review of your PR

[github-actions]

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[bmarty]

FTR we have this settings in Element Classic (but not defaulting to hiding message content in notification):

[jmartinesp]

@mxandreas another PR to check once you're back 😅 .

We were also discussing this behaviour earlier and a valid point was whether we want to link the 2 options and only have this hiding of notification content option available if there's a PIN code, or if it should always be present (disabled by default) and the user can change it at any time.

[mxandreas]

ATM you can still read and reply from the notifications on new messages even when the app is locked, which almost defeats the entire purpose of having an app PIN lock.

I am curious about the use cases or real life situations for this one. I understand the phone is unlocked (otherwise one could hide content in notifications, right), then a new message arrives and then you would not want its content to be shown? A few examples would be appreciated.

[jmartinesp]

I think when this was asked before it was for the case where you have notifications as heads up (so, displaying above everything else even if you don't open the notification drawer) and someone is looking at your phone/recording it somehow.

So you want to know there is new content in the app, you just don't want to display the content unless you unlock the app.

[mxandreas]

and someone is looking at your phone/recording it somehow

I understand that this can theoretically happen - you show your phone to someone and because of bad timing some sensitive message appears but for me this is an edge case. So, unless there is a very clear scenario in which it happens regularly and there is no workaround, I'd not spend time on it.