Implement experimental encrypted state events.

[kaylendog]

Adds support for MSC3414-esque encrypted state events.

• Updates matrix-sdk-crypto-wasm to 15.3.0 which includes support for encrypting state events.
• Adds an MatrixClient.enableEncryptedStateEvents flag to configure top-level behaviour.
• Modifies MatrixClient.sendStateEvent to call into the WASM SDK if encryption is enabled.
• Adds MatrixEvent.getWireStateKey, analagous to MatrixEvent.getWireContent.

This can be split into multiple PRs for ease of reviewing if required!

Checklist

• Tests written for new code (and old code if feasible).
• New or updated public/exported symbols have accurate TSDoc documentation.
• Linter and other CI checks pass.
• Sign-off given on the changes (see CONTRIBUTING.md).

[richvdh]

Please don't put words like "feat" in titles of matrix-js-sdk PRs: such titles end up the changelog, and although implementing this has indeed been quite a feat, it doesn't do to brag about it ;)

(also https://richvdh.org/conventional-commits-considered-harmful.html but that's beside the point)

[andybalaam]

Looking good - a few smallish points to work through together.

Comments addressed.

[andybalaam]

All good, thanks!

[andybalaam]

@kaylendog the "downstream" checks failed, meaning when we compile Element Web with this change something went wrong.

The error is:

Error: matrix-js-sdk/src/client.ts(6642,96): error TS2322: Type 'StateEvents[K]' is not assignable to type 'IContent | undefined'.
  Type 'StateEvents[K]' is not assignable to type 'IContent'.
Error: src/components/views/settings/tabs/room/SecurityRoomSettingsTab.tsx(177,83): error TS2345: Argument of type '{ algorithm: "m.megolm.v1.aes-sha2"; }' is not assignable to parameter of type 'RoomEncryptionEventContent'.
  Property '"io.element.msc3414.encrypt_state_events"' is missing in type '{ algorithm: "m.megolm.v1.aes-sha2"; }' but required in type 'RoomEncryptionEventContent'.
error Command failed with exit code 2.

(From https://github.com/matrix-org/matrix-js-sdk/actions/runs/17948535831/job/51041145148 , accessed via the "Details" link above.)

I think this is a valid error: your new property should definitely be optional, so events from clients that don't support it still work ok.

[kaylendog]

All fixed!

[andybalaam]

Awesome, please rebase and force-push and I'll merge