> arguably I shouldn't have all these long-lived branches in the first place (but it works well for me, so...)
Given that this scenario is common for you but sounds contrived to others, I would argue that this doesn't work well for you. It's just familiar enough that you're willing to deal with some pain.
Short-lived feature branches sidestep this hell. Longer-lived projects can almost always be partitioned into a series of shorter mergeable steps. You may need support/buy-in from your manager, I hope you get it.
It's not a organisational/manager problem; it's just how I like to work. I often work on something and then I either get bored with it or aren't quite sure what the best way is to proceed, so I work on something else and come back to it later (sometimes hours later, sometimes days, weeks, sometimes I keep working on it until I get it right). I do this with my personal projects as well where I can do whatever I want.
I know some people think this is crazy, but it works well for me and I'm fairly productive like this, usually producing fairly good code (although I'm not an unbiased source for that claim).
In the end I don't want to radically change my workflow to git or other tooling; I want the tooling to adjust to the workflow that works well for me.
Given that this scenario is common for you but sounds contrived to others, I would argue that this doesn't work well for you. It's just familiar enough that you're willing to deal with some pain.
Short-lived feature branches sidestep this hell. Longer-lived projects can almost always be partitioned into a series of shorter mergeable steps. You may need support/buy-in from your manager, I hope you get it.