typecheck

It is the first stage of sup3rapp's verification chain for two reasons: it is fast, and it produces the most precise diagnostics of any stage. A failure names a file, a line, an error code and the exact mismatch. That precision is what makes an automatic repair loop work rather than flail.

Typechecking is unusually well suited to catching what language models get wrong. The characteristic model error is not nonsense — it is code that reads correctly and quietly assumes something that is not guaranteed. A field that might be null, used as though it never is. A function called with the right shape of argument but the wrong one. Both are invisible to a reviewer skimming for style and immediate to a compiler.

What it cannot do is judge intent. A typechecked program can be entirely wrong: it can charge the wrong customer, calculate a date incorrectly, or expose data it should not. The types were consistent. That is all the stage claimed.

Which is why it is the first stage and not the only one. Tests check behaviour, the production build checks that it compiles the way it will ship, and the smoke test checks that it starts.