Thanks.
I didn’t touch the validator at Farringdon (though the signs telling me I should did have me confused until I read your excellent article on the subject).
What I did was exit the station to grab a coffee and some provisions from the Co-Op before re-entering and continuing to City Thameslink (a necessity ever since the Co-Op at Ludgate Circus closed down). I’m usually quite happy for that to be charged either as a continuation or a separate journey, since daily capping means it costs me the same either way (providing I’ve touched in, of course).