Just a guess, but to me it sounds like you're trying to do too much at once. When trying something like this:

> lots of careful code of registering and unregistering callbacks, some careful thread synchronisation (callbacks get called in another thread), thinking about sane exception handling in async code. Fiddly but not rocket science.

I'd expect CC to fail this when just given requirements. The way I use it is to explicitly tell it things like: "Make sure to do Y when callback X gets fired" and not "you have to be careful about thread synchronisation". "Do X, so that Exceptions are always thrown when Y happens" instead of "Make sure to implement sane Exception handling". I think you have to get a feeling for how explicit you have to get because it definitely can figure out some complexity by itself.

But honestly it's also requires a different way of thinking and working. It reminds me of my dad reminiscing that the skill of dictating isn't used at all anymore nowadays. Since computers, typing, or more specifically correcting what has been typed has become cheap. And the skill of being able to formulate a sentence "on the first try" is less valuable. I see some (inverse) parallel to working with AI vs writing the code yourself. When coding yourself you don't have to explicitly formulate everything you are doing. Even if you are writing code with great documentation, there's no way that it could contain all of the tacit knowledge you as the author have. At least that's how I feel working with it. I just got really started with Claude Code 2 months ago and for a greenfield project I am amazed how much I could get done. For existing, sometimes messy side projects it works a lot worse. But that's also because it's more difficult to describe explicitly what you want.

> The way I use it is to explicitly tell it things like: "Make sure to do Y when callback X gets fired" and not "you have to be careful about thread synchronisation". "Do X, so that Exceptions are always thrown when Y happens" instead of "Make sure to implement sane Exception handling".

At this point I'm basically programming in English, no? Trying to squeeze exact instructions into an inherently ambiguous representation. I might as well write code at this point, if this is the level of detail required. For this to work, I need to be able to say "make this thread-safe", maybe "by using a queue". Not explaining which synchronisation primitive to use in every last piece of the code.

This is my point actually. If I describe the task to accuracy level X, it still doesn't seem to work. To make it work, perhaps I need to describe it to level Y>X, but that for now takes me more time than to do it myself.

There's lots of variables here, how fast I am at writing code or planning structure, how close to spec the things needs to be, etc. My first "vibe code" was a personal productivity app in Claude Code, in Flutter (task timing). I have 0 idea about Dash or Flutter or any web stuff, and yet it made a complete app that did some stuff, worked on my phone, with a nice GUI, all from just a spec. From scratch, it would take me weeks.

...though in the end, even after 3 attempts, the final thing still didn't actually work well enough to be useful. The timer would sometimes get stuck or crash back down to 0, and froze when the app was minimised.