Added the second dose of finishing hops just now, 35g Citra again via the top after de-pressurising the vessel. This time there was a substantial buildup of foam as I neared zero pressure and took the lid off, and I think if I hadn’t have thrown in the hops and screwed the top back on quickly there would have been a mess to clear up.
As it stands I may have rushed the refitting of the lid because the vessel wouldn’t hold pressure when the top was back on, so I had to remove it a second time. No issues after re-seating it, keeping pressure fine and back up to 12 PSI. I’m not sure if I should count the cold-crashing as part of the dry-hop duration (though interesting experiments have been done) so I might cold crash a day early and only for 24 hours in order to retain as much of the good hops as possible.