Every tool on this list solves a real problem. None of them solves the same problem as FST. They are not alternatives to each other — they are different layers, and understanding what each layer does and does not do is the fastest way to see where FST fits.
Your agent writes code. Tests pass. You ship. That loop works — until the day something breaks in a part of the codebase the agent was never supposed to touch, and the only record of what happened is a chat transcript.
FST interrupts you when the answer changes the safe path. Not when it is processing, not when it is running checks, not when it has a routine implementation detail to handle. Only when your input changes what the agent is allowed to do next.
You know the feature you want, but not yet which direction should become the product.
That is the moment where AI is most tempting and most dangerous: it can build a plausible version fast, but a plausible version can quietly become the direction before you have compared the alternatives.