I have restarted the same project four times — how do you decide it is finished rather than picking it up again?

The "everything already in it" part is the bit doing the damage, and it is worth being blunt: those months are gone whatever you decide. They are not an asset in the project, and continuing does not recover them. The only question available to you is what the next three weeks are worth, compared with the next three weeks spent on anything else.

A test that helped me: if a friend described this project to you — four restarts, no features, months of maintenance, still excited about the idea — what would you tell them? People are consistently able to answer that about someone else and unable to answer it about themselves, which tells you the difficulty is not analytical.

A second one, which is harder: would you start it today, knowing what it takes to maintain? If the answer is no, you are not choosing to build it, you are declining to stop.

One thing I would push back on in your framing, though. You say the idea is still good. If that is true, the idea can survive the codebase dying. Ideas are not stored in repositories. If you genuinely want to build this thing one day, killing four years of accumulated rot and starting clean when you actually have the time is a completely reasonable plan — and it is a different decision from another restart, because it does not commit you to three weeks of repair first.

The fact that four restarts produced no features is the answer, and it is worth looking at directly rather than around.

You have run the experiment four times. Each time the result was the same: enthusiasm, repair, exhaustion, stop. That is not bad luck repeated four times — it is a reliable finding about this project and this life, and the only thing that varies is what you tell yourself at the start of each attempt.

The question that unstuck me was not "is the idea good". Ideas are cheap and yours is probably fine. It was: what would have to be different for attempt five to end differently? Not vaguely — specifically. More time? You do not have more time. Less rot? The rot comes from the gaps, and the gaps come from the stopping. A collaborator? Then the task is finding one, not restarting.

If you cannot name something concrete that changed, attempt five is attempt four with a different date, and you already know how it ends.

When I finally shut mine down the surprise was that it was not sad, it was relief. The project had stopped being a thing I was building and become a debt I carried, and every month I did not open it was a small failure. Ending it deliberately turned a recurring guilt into one bad afternoon. That week was the most productive I had that year, purely because the background process stopped running.