The reader for the CosmosDB ChangeFeed [emits an (indicative, depends on clock sync) "age" stat per batch retrieved](https://github.com/jet/propulsion/blob/97365de328e8fa3738983793b39271e7464dde76/src/Propulsion.Cosmos/CosmosSource.fs#L25), which can be very useful as an indicator for troubleshooting The same should be added to [the equivalent logging in `EventStoreReader`](https://github.com/jet/propulsion/blob/66b7b403ba64b74b1a87867fbb5dffe7929ac7cb/src/Propulsion.EventStore/EventStoreReader.fs#L165)