Race condition on recorded notification from abacus

[egli]

When receiving a recorded notification from abacus we check if the status is "structured" and if yes start the encoding process. However the status is only changed once the encoding is finished. This can take several minutes, i.e. the window is wide open for a race condition. It would probably make sense to use a similar mechanism as when repairing, i.e. store an intermediate state in the cache and invalidate it once the encoding is finished.