Element-R: creates new cross-signing identity if initial /keys/query takes longer than 1s

[richvdh]

Sometimes, when you log in, Element-R skips straight through to the home page rather than letting you verify your new device with the cross-signing keys.

I think the problem is related to the fact we only wait for a second for /keys/query requests to take place... and we don't even start making them until the first /sync completes.

[richvdh]

What happens here is:

• MatrixChat.postLoginSetup calls MatrixClient.userHasCrossSigningKeys. Per the description, and Cannot distinguish users who have no cross-signing key and users whose /keys/query remains in flight matrix-org/matrix-rust-sdk#2263, this races and incorrectly returns false.
• Hence we enter view E2E_SETUP. In that state, we display an E2ESetup component, which shows a CreateCrossSigningDialog component, which unconditionally calls MatrixClient.bootstrapCrossSigning on mount.
• bootstrapCrossSigning doesn't (yet) check if there are private keys in secret storage (https://github.com/matrix-org/matrix-js-sdk/blob/e82b5fe1dbf5302ad70c02f3d648f20778e12119/src/rust-crypto/CrossSigningIdentity.ts#L44), so merrily tramples over the existing keys.

So there are two problems here; one is the incorrect result of userHasCrossSigningKeys which causes us to call bootstrapCrossSigning in the first place, and the other is that bootstrapCrossSigning does not check secret storage (now raised as #25781).