Notification 'red' badge count is flawed in E2EE rooms

[ara4n]

You can only correctly calculate badge counts for mentions & keyword push rules if you decrypt every message in an E2EE room on the client. Currently if there is a gappy sync (due to the app being offline overnight, or the client failing to keep up with the server) then messages deliberately get dropped. Therefore the 'red' badge count for missed notifications is wrong (and the NotifPanel is wrong) whenever the app awakes in the morning - which is when you want the badge counts to be the most correct.

Instead we should spider the E2EE rooms in the background in order to calculate the right notification count. Luckily we have the code to do this already for Seshat - but we need to actually hook it up on both Web & Desktop so that it triggers badge count calculations as it spiders, so we at last get the correct badge counts.

cc @manuroe and @bmarty for iOS & Android, as the same problem exists there (but is less pronounced given gappy syncs are somewhat less common given people tend not to turn off or disconnect their phones as often as they do their laptops).

cc @gsouquet as this overlaps somewhat with his decrypt-on-demand work in matrix-org/matrix-js-sdk#1684

[ara4n]

(is it really minor that your notifications plain lie about whether you've been notified or not?)

[babolivier]

I also disagree with this bug being categorised as minor. Since I close my work Element session when I'm not working (which I assume a fair amount of people using Element for work would do), this means that I'll need to go through each of my encrypted rooms manually to make sure I haven't missed a notification at least once a week (after the weekend - I got hit by it on Monday) and each time I come back after some time off. IMHO this doesn't paint a great picture of Element in terms of reliability if using it for work means it's likely to drop notifications on the floor at least once a week.

[MadLittleMods]

(from #9069) Also related to matrix-org/matrix-spec-proposals#1796

[richvdh]

Instead we should spider the E2EE rooms in the background in order to calculate the right notification count.

For links: this also came up in the context of discussions around MSC3952 (matrix-org/matrix-spec-proposals#3952 (comment)).

[richvdh]

Closely related: #6874.

[MadLittleMods]

👍 Very annoying to have my Element Web missing notifications which I know they were there from over the weekend. Subtle/insidious way to miss notifications.

Element Web that was running the whole time but was refreshed and is now missing red badge for the Moderation Internal room	Element desktop that ran the whole time and shows mentions for Moderation Internal