[Story] Show that I have been mentioned in the push notification

[VolkerJunginger]

Story

As a user that has been mentioned I want to see this in the push so that I can react fast.

Figma link: TBD

Acceptance criteria

• show that user has been mentioned in the push

Size estimate

M

Dependencies

MSC

• MSC4028: Push all encrypted events except for muted rooms matrix-org/matrix-spec-proposals#4028
• Support MSC4028 (Push all encrypted events except for muted rooms) matrix-org/synapse#15847
• https://github.com/matrix-org/internal-config/issues/1469

Preconditions

• We need backend support for the new push rule but we can simulate the behavior by setting a similar push rule at the room level.

Open questions

### Questions
- [x] Can we implement [MSC4028](https://github.com/matrix-org/matrix-spec-proposals/pull/4028) in Synapse? -> Yes it is coming
- [x] What kind of copy should we display for the mention in push notifications?
- [x] Would the copy be different between the mention of the reading user and the mentions of other users if multiples are contained?
- [x] ~~We need to call this [API](https://spec.matrix.org/v1.8/client-server-api/#put_matrixclientv3pushrulesscopekindruleidenabled) to allow the MSC 4028 push rule to be enabled or disabled~~ we will not need it given the new MSC spec
- [x] The push rule might not even exist on the server so we would need to also have an API that allows us to check if it is present or not (otherwise the Mentions Only option is probably useless to have for encrypted rooms)
- [ ] Could we consider this story done if the feature is not enabled on matrix.org?

Subtasks

### Android
- [ ] https://github.com/vector-im/element-x-android/issues/1451
- [ ] https://github.com/vector-im/element-x-android/issues/1794

### iOS
- [ ] https://github.com/vector-im/element-x-ios/issues/1825
- [ ] https://github.com/vector-im/element-x-ios/issues/2078

### Rust
- [ ] https://github.com/matrix-org/matrix-rust-sdk/issues/2606
- [ ] https://github.com/matrix-org/matrix-rust-sdk/issues/2834
- [ ] https://github.com/matrix-org/matrix-rust-sdk/pull/2840

### Design
- [x] How the mention text is displayed

• QA signoff on completion
• Design signoff on completion
• Product signoff on completion

[manuroe]

Can we implement MSC4028 in Synapse?

@pmaier1 What do you think about this open question we have for this story? This is backend dependency we need to make mentions work in e2e rooms.

[pmaier1]

Yes, we're working on this here.

[Velin92]

What is the expected behaviour in how we display the user mention in the push notifications? What is the expected copy that replaces the user mention link? (This is actually something that we can do at a copy level by just detecting the permalink, however we would only be able to get the user id of the mention data coming from the SDK) Is there any additional copy too?
@manuroe
@VolkerJunginger
@amshakal

EDIT:
Actually we also able to use the original string without the need of the display name, that wrapped the link if the mention was sent as an hyperlink for example Test , this is usually the display name however a mention can also be just the url directly, which means that this solution is not always going to work, so we might still need the display name provided by the SDK

[manuroe]

@giomfo, can you share here the trick to simulate matrix-org/matrix-spec-proposals#4028 while the HS is not yet ready, please?

[giomfo]

To simulate MSC4028, I plugged on an existing button the following code (in the Legacy iOS-client) to add/remove a specific Override push rule.
This rule is added only for the current user, it force the server to push all encrypted event for this account. You just have to define a unique ID (here "encrypted_marcel"):

            if let rule = notificationCenter?.rule(byId: "encrypted_marcel") {
                removePushRule(rule: rule, completion: completion)
                return
            } else {
                notificationCenter?.addOverrideRule(
                    withId: "encrypted_marcel",
                    conditions: [["kind": "event_match", "key": "type", "pattern": "m.room.encrypted"]],
                    notify: true,
                    sound: false,
                    highlight: false
                )
                completion()
                return
            }

In parallel I used a web client to configure some rooms in the Mention&Keywords mode.
Then my mobile client was able to receive all encrypted events and displayed only the mentions for these rooms.

[hughns]

Further to this topic coming up in the weekly BWI drop syncs I have made https://github.com/matrix-org/internal-config/issues/1469 to track the request to enable it on matrix.org. There were various discussions in rooms but hopefully this issue can be authoritative on the formal request.

I asked @manuroe in the EX Leads room but it is probably better to ask here:

1. What status does MSC4028 need to be in for delivery at the end of this month? It is currently a draft MSC that needs some work based on feedback from the implementation that was done in Synapse.
2. What level of testing is actually needed ahead of the delivery? Whilst matrix.org is convenient can these needs be met through some other homeservers (beta.matrix.org, element.io etc.)

CC @giomfo as the MSC author.

[hughns]

One further thought: if it is needed on matrix.org would it be acceptable to make it only apply to a preconfigured list of users? (this is an approach used for some other features).