Message retention implementation tracking

[mredig]

In implementation for https://github.com/matrix-org/matrix-spec-proposals/blob/matthew/msc1763/proposals/1763-configurable-retention-periods.md, I intend to break this up into at least two PRs:

1. endpoint retrieval and event/state handling
2. execution of removing expired messages per retention policy

This issue is just for tracking the bigger task, re @stefanceriu's suggestion.

[Hywan]

Thanks!

That's a good idea. Feel free to ping us whenever you need assistance.

[mredig]

This is past due, but for record keeping, here are the ruma PRs that were required for this feature:

• Support for MSC1763 ruma/ruma#2554 (comment)
• client-api: Add constructors to get_retention_configuration Request and Response ruma/ruma#2563

and bumping this sdk's reference to its ruma fork here:

• chore: bump Ruma to its latest main #6901

[mredig]

My updated plan is to break this into a couple more PRs than originally intended.

Here's the plan:

1. Room and RoomInfo base retention state tracking - Message Retention RoomInfo and Room State Tracking #6905
2. Server config retrieval - feat(sdk): add server retention config endpoint #6908
3. effective policy calculation - feat(sdk): calculate retention policy per room #6919
4. local cache purge from the sdk
5. ffi bindings