> eventually the Pomodoros inevitably give way to extended sessions with flow.

I have also found this to be a great way to trick my mind into working. Promise myself "just one" pomodoro, then I can go do something else. If I get that first session started, by the end of it I don't want to stop even for the five-minute break, and then next thing I know four pomodoros have gone by and, lo and behold, the opposite of the usual procrastination timesuck: I actually spent two hours working on the thing without thinking about it! The mind is such a weirdo like that.

That's a good perspective. I drifted away from pomodoro's precisely because I found the intervals too be a bit too rigid and the breaks occurred when I'd be in the middle of something. Instead using one or more as a bootstrap for productivity is something I hadn't considered, but it seems obvious now.

I'll admit they kind of fade in and out of usefulness for me. But I always feel free to bleed into a break, too, if I'm right smack in the middle of something. I have found it important to actually take the break at some point, though. Timer rings, take a minute or two to finish the thought, then reset the timer for your break.