When the gravel bike's transmission starts treating shifter input as a suggestion for eventual action rather than as an immediate command, that's an indicator that it's time for a new chain. A quick check with a chain stretch gauge confirmed it – not in the red zone yet, but edging onto it – and the change went smoothly. No need to swap the cassette or chainrings yet, not if you change out a chain in time. Usually get about three chains to the rest of the drivetrain components, before those need swaps too. One down, two to go. And yes, I do keep a log book of these things, because keeping track of multiple bikes would be impossible otherwise.
The ride today was noticeably more snappy. Funny how these little wear items creep up on you.