that's how stratum works: it gives the miner work to do, including all the stuff that must be put into the block header, to be hashed.
the miner doesn't connect to a coin daemon, so all the info must come from the pool thru stratum.
look for more info about stratum, extranonce (1 e 2), merkleroot, the block header in general.
im already knew all of this couple of years ago. thats why im asking coder/pool developer how this works on pool side. my question here was addressed to Tanguy Pruvot. becouse i cant send private message to him.