EX: Inform users when fixing "key storage out of sync" fails

[richvdh]

For example:

1. On a different device:
   1. reset cryptographic identity
   2. set up recovery
   3. using the developer tools, edit the m.cross_signing.user_signing account data item to remove the content of the encrypted object, thus: {"encrypted": {} }
2. Back on the device under test, enter the newly-created recovery key to re-verify
3. Observe "Your key storage is out of sync" toast; click "Continue"
4. Enter recovery key, click "Continue"
5. Back to step 3

In the logs, there is this line:

18:14:54.036  I  matrix_sdk_crypto::store: Successfully imported the private cross-signing keys status=CrossSigningStatus { has_master: true, has_self_signing: true, has_user_signing: false } | crates/matrix-sdk-crypto/src/store/mod.rs:1321 | spans: recover > import_secrets{self=SecretStore { key: SecretStorageKey { storage_key_info: SecretStorageKeyEventContent { key_id: "JsOhg6wGuD18Qjv235PUioHOXojWNbi7", name: None, algorithm: V1AesHmacSha2(SecretStorageV1AesHmacSha2Properties { iv: Some("kR2sRxtvSEIX4xZWujQkrg"), mac: Some("ESubXhxa3xvA4oUMBfIiiS47U6TO9jdXXF3P4Rry0AI") }), passphrase: None }, .. }, .. } user_id=@af:xps9320.sw1v.org device_id=ZZTJDJERZH}

Obviously, the user-signing key is not being imported. The problem is that the process is failing silently.

[richvdh]

See also element-hq/element-web#29229, which tracks the same thing on Element Web.

See also also #4728, which is a different cause of the "out of sync" toast getting stuck.